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1. Seismicity in far western Nepal reveals flats and ramps along the Main Himalayan Thrust

Author: Magali Riesner, Chintan Timsina, M. Laporte, Bharat Prasad Koirala, C Duverger, T. Kandel, Mukunda Bhattarai, Hélène Lyon-Caen, Laurent Bollinger, L. B. Adhikari, R. Hoste-Colomer, Jean Letort, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Laboratoire de Détection et de Géophysique (CEA) (LDG), DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, and Department of Mines and Geology, Lainchaur, Kathmandu
Subjects: geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Front (oceanography), [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Thrust, Induced seismicity, Fault (geology), 010502 geochemistry & geophysics, 01 natural sciences, Tectonics, Geophysics, 13. Climate action, Geochemistry and Petrology, Regional studies, Period (geology), Seismic cycle, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: SUMMARYUnravelling relations between lateral variations of mid-crustal seismicity and the geometry of the Main Himalayan Thrust (MHT) system at depth is a key issue in seismotectonic studies of the Himalayan range. These relations can reveal along strike changes in the behaviour of the fault at depth related to fluids or the local ramp-flat geometry and more generally of the stress build-up along the fault. Some of these variations may control the rupture extension of intermediate, large or great earthquakes, the last of which dates back from 1505 CE in far western Nepal. The region is also associated to lateral spatio-temporal variations of the mid-crustal seismicity monitored by the Regional Seismic Network of Surkhet–Birendranagar. This network was supplemented between 2014 and 2016 by 15 temporary stations deployed above the main seismic clusters giving new potential to regional studies. Both absolute and relative locations together with focal mechanisms are determined to gain insight on the fault behaviour at depth. We find more than 4000 earthquakes within 5 and 20 km-depth clustered in three belts parallel to the front of the Himalayan range. Finest locations reveal close relationships between seismic clusters and fault segments at depth among which mid-crustal ramps and reactivated tectonic slivers. Our results support a geometry of the MHT involving several fault patches at depth separated by ramps and tear faults. This geometry most probably affects the pattern of the coseismic ruptures breaking partially or totally the locked fault zone as well as eventual along strike variations of seismic coupling during interseismic period.
Published: 2021
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2. The Preseismic and Postseismic Phases of the 700‐km Deep M7.9 Bonin Islands Earthquake, Japan

Author: D. Marsan, Michel Bouchon, Hélène Lyon-Caen, Shamita Das, Alexandre Schubnel, Blandine Gardonio, Aitaro Kato, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
Subjects: Geophysics, 010504 meteorology & atmospheric sciences, Subduction, 13. Climate action, [SDU]Sciences of the Universe [physics], General Earth and Planetary Sciences, 010502 geochemistry & geophysics, 01 natural sciences, Geology, Seismology, 0105 earth and related environmental sciences, Deep-focus earthquake, Foreshock
Abstract: International audience; The 30 May 2015 M w 7.9 Bonin Islands earthquake, Japan, is one of the largest deep-focus earthquakes ever recorded. Its occurrence, close to 700-km depth, in an area without any known historical seismicity, along with its magnitude, was a surprise to scientists. Deep earthquakes are generally believed to have few aftershocks and no foreshocks. Here, we explore the earthquake productivity in the hypocentral surroundings and detect 49 not previously identified earthquakes, 28 of which occurred during an accelerating preseismic phase that started 3 months prior to the main shock. This is the first time that such foreshock activity has been observed for a deep earthquake. The preseismic and postseismic activity suggests transformational faulting within a metastable olivine wedge (MOW) inside the slab at depth as the triggering principal mechanism for this deep earthquake sequence, the seismicity starting where the backward bending of the subducting Pacific plate is maximum. Plain Language Summary Deep earthquakes have been puzzling seismologists for almost a century, since their discovery in the 1920s. Earthquakes deeper than 50 km represent about 25% of the global seismicity, and deep-focus earthquakes are defined as those located at 300-km depth or more. They can be exceedingly large and occur at temperatures and pressures where sliding and fracture are inhibited, thus the brittle fracture/friction mechanism, valid in Earth's crust, cannot hold. Despite their abundance, the physical mechanism behind deep-focus earthquakes is still a subject of ongoing debate. The Bonin Islands earthquake (30 May 2015, M w 7.9) occurred at 680-km depth in a previously quiet area. In order to better understand why and how it occurred there, we searched for previously unknown earthquakes in the surroundings. For the first time, we identify a preseismic phase preceding such a very deep-focus earthquake. The location of the newly detected earthquakes reveals the geometry of the slab at depth, and their spatiotemporal distribution supports transformation of metastable olivine as the rupture initiation process.
Published: 2020
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3. Tracing the seismic history of Sant’Agata del Mugello (Italy, Tuscany) through a cross-disciplinary approach

Author: Andrea Arrighetti, Hélène Dessales, Arnaud Montabert, Julien Clément, M. Lancieri, Hélène Lyon-Caen, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), PSE-ENV/SCAN/BERSSIN, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Archéologie et Philologie d'Orient et d'Occident (AOROC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL), Università degli Studi di Siena = University of Siena (UNISI), and PSN-EXP/SES/LMAPS
Subjects: 010506 paleontology, Archeology, architecture, [SHS.ARCHEO]Humanities and Social Sciences/Archaeology and Prehistory, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Event (relativity), Magnitude (mathematics), Induced seismicity, Tracing, 01 natural sciences, Nave, Bell tower, 0601 history and archaeology, building stratigraphy, structural analysis, Architecture, 0105 earth and related environmental sciences, Central Italy, 060102 archaeology, historical seismicity, historical sources, 06 humanities and the arts, damage mechanisms, AGATA, Geology, Seismology
Abstract: International audience; Historical seismicity is mainly defined from historical sources which are not always available. Yet historical buildings are a unique opportunity to record and study effects of past earthquakes at a given place. An innovative methodology is defined to improve knowledge of local historical seismicity. Such a methodology is based on an interdisciplinary approach combining: analysis of historical sources, stratigraphic analysis and structural analysis of an historical building. The church of Sant’Agata del Mugello (Italy, Tuscany) is considered as a case of study. The stratigraphic analysis is performed by identifying the repairs using the RECAP methodology. 80 repairs units using 13 building techniques are identified in the church. The identified repairs are associated with unknown events, earthquakes or routine reconstructions. When post-earthquake reconstructions are found, damage mechanisms are associated with them. 13 constructive phases of the church have been traced combining stratigraphic analysis and historical sources. A proto-church was built before 948 A.D. and is nowadays below the current one. The first phase of the current church appears between the 9th and the 12th century. A significant event of unknown origin occurred during the 12th century which probably led to an important collapse and then a significant reconstruction of the church. The church is then deeply affected by the 1542 seismic event (epicentral macroseismic intensity 9, deduced magnitude 6.02) which resulted in the collapse of the upper part of the bell tower and the two lateral chapels as well as the overturning of the front wall and of the two lateral walls of the nave. The 1611 seismic event (epicentral macroseismic intensity 7, deduced magnitude 5.1) damaged the upper part of the bell tower as described in historical records. In spite of the confirmed occurrence of seismic events in the area from the middle of the 17th century and the beginning of the 20th century, no information relating seismic damage of the church has been found in historical records nor in the startigraphic analysis. The most important earthquake which struck the area on June 19th, 1919, produced only some small cracks in the church (magnitude 6.38).
Published: 2020
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4. GPS constraints on deformation in northern Central America from 1999 to 2017, Part 2: Block rotations and fault slip rates, fault locking and distributed deformation

Author: Douglas Hernández, Robert McCaffrey, Hélène Lyon-Caen, Manuel Rodriguez Maradiaga, Cécile Lasserre, E. Molina, Beatriz Cosenza Muralles, Vladimir Kostoglodov, A. P. Ellis, Charles DeMets, Jeffrey Rivera, Alejandra Staller, Robert D. Rogers, Basil Tikoff, Marco Guzmán-Speziale, N. E. Lord, Peter LaFemina, Pierre Briole, Omar Flores, Dpt of Geosciences Wisconsin, University of Wisconsin-Madison, Department of Geology [Portland], Portland State University [Portland] (PSU), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Universidad de San Carlos de Guatemala, Centro de Geociencias [Queretaro], Universidad Nacional Autónoma de México (UNAM), Instituto de Geofísica, Department of Geosciences, Pennsylvania State University (Penn State), Penn State System-Penn State System, Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Universidad Nacional Autónoma de Honduras (UNAH), Universidad Mariano Galvez, California State University [Stanislaus], Universidad Politécnica de Madrid (UPM), Department of Geoscience, Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF), Universidad Nacional Autónoma de Honduras, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM), and Penn State Department of Geosciences
Subjects: geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, business.industry, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Deformation (meteorology), Fault (geology), 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, Geochemistry and Petrology, Earthquake hazard, Block (telecommunications), Global Positioning System, Fault slip, business, Seismic cycle, Seismology, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract: International audience
Published: 2019
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5. SHERIFS: Open‐Source Code for Computing Earthquake Rates in Fault Systems and Constructing Hazard Models

Author: Thomas Chartier, Hélène Lyon-Caen, Oona Scotti, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Laboratoire de géologie de l'ENS (LGE), Département des Géosciences - ENS Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: Seismic hazard analysis, Computation tree logic, 010504 meteorology & atmospheric sciences, Computer science, Probabilistic logic, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Slip (materials science), Active fault, Induced seismicity, Python (programming language), Fault networks, 010502 geochemistry & geophysics, computer.software_genre, 01 natural sciences, Geophysics, Seismic hazard, Data mining, Fault model, computer, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, computer.programming_language
Abstract: International audience; Modeling the seismic potential of active faults and their associated epistemic uncertainties is a fundamental step of probabilistic seismic-hazard assessment (PSHA). Seismic hazard and earthquake rate in fault systems (SHERIFS) is an open-source python code that builds hazard models including earthquake ruptures involving several fault sections or fault-to-fault (FtF) ruptures. It contains user-friendly tools to calculate the annual rate of FtF ruptures in a fault system based on the slip-rate estimates and accounting for associated background seismicity. SHERIFS applies a forward incremental approach following three rules: (1) the FtF ruptures allowed in the fault system are defined as input by the user and explored randomly, (2) the magnitude-frequency distribution of the modeled seismicity in the fault system must follow an imposed shape, and (3) the slip-rate budget attributed to each fault section must be preserved in the calculation if the first two rules allow it. Indeed, in some cases, a fraction of the slip-rate budget must be considered as being spent in non-mainshock events such as creep or postseismic slip. Background seismicity rates are defined by the hazard modeler as the ratio of seismicity occurring on the modelled faults for different ranges of magnitude. Given a coherent set of input hypotheses, SHERIFS allows end users to build the seismic-hazard fault model thanks to an interactive user-friendly interface. It aims to help interactions between field data collectors and hazard modelers to explore and weight epistemic uncertainties affecting the input hypotheses. To do so, SHERIFS includes tools to compare modeled earthquake rates with the available local data (earthquake catalog and paleoseismological data). This comparison can be used to weigh different hypotheses explored in a logic tree and discard the hypotheses that are not in agreement with the data. SHERIFS's outputs are in a format that can be used directly as inputs for PSHA in the OpenQuake engine (Pagani et al., 2014).
Published: 2019
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6. Large Scale Observations and Modeling of Strain Partitioning in Guatemala from SAR Interferometry

Author: Ana Beatriz Cosenza-Muralles, Cécile Lasserre, Charles DeMets, Francesco De Zan, Robert Shau, Homa Ansari, Hélène Lyon-Caen, Kurt Feigl, Alessandro Parizzi, Lasserre, Cécile, Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, GEODESY AND GRAVITY, slip rate, MARINE GEOLOGY AND GEOPHYSICS, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Tectonics, GEOMAGNETISM AND PALEOMAGNETISM, 3040 Plate tectonics, SEISMOLOGY, [SDU.STU.TE] Sciences of the Universe [physics]/Earth Sciences/Tectonics, 1209 Tectonic deformation, global, 1525 Paleomagnetism applied to tectonics: regional, 7230 Seismicity and tectonics, SAR Interferometry, [SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], slip partitioning
Abstract: International audience; The zone of interaction between the Cocos (CO), Caribbean (CA) and North America (NA) plates in Guatemala is defined by the sub-parallel Motagua and Polochic strike-slip faults, a series of north-south-trending extensional grabens immediately south of the Motagua Fault, the Middle America trench, and faults within the Middle America volcanic arc. Historical earthquakes associated with these faults include the destructive 1976 Mw 7.5 earthquake along the Motagua fault and the 2012 Mw 7.5 Champerico thrust earthquake. The latest published GPS-based present-day kinematic model of the region shows that about two-thirds of the strain accumulation from the NA/CA relative motion concentrates on the Motagua fault and one third across the Polochic fault, suggesting that slip varies with time as a result of mechanical interactions within the Motagua-Polochic fault system. As part of the efforts to quantify the present-day kinematics and slip behavior of these faults, we use interferometric synthetic aperture radar (InSAR) to measure the strain rates across faults in Guatemala and to constrain slip partitioning among them. We processed L-band ALOS-1 images spanning from 2006 to 2011, and C-band Sentinel-1 images spanning from 2015 to 2019, from ascending and descending tracks covering the Polochic and Motagua faults, the Ipala and Guatemala City grabens, and part of the volcanic arc to the south. We are using the New Small temporal and spatial baselines (NSBAS) workflow to compute the interferograms, make tropospheric and ionospheric corrections, and perform time-series analysis. We present the first InSAR-based maps of interseismic velocity for this region, which will contribute to the refinement of interseismic locking estimates across the Motagua-Polochic fault system, the subduction zone, and other nearby faults.
Published: 2019

7. Imaging the Moho and the Main Himalayan Thrust in Western Nepal With Receiver Functions

Author: György Hetényi, L. B. Adhikari, Shiba Subedi, Laurent Bollinger, Jérôme Vergne, Hélène Lyon-Caen, Véronique Farra, Ratna Mani Gupta, Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Université de Lausanne (UNIL), Ecole et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), National Seismological Centre, Katmandhu, Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université de Lausanne = University of Lausanne (UNIL), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Thrust, Crust, 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, Receiver function, General Earth and Planetary Sciences, Foothills, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: International audience; The crustal structure of Western Nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations. The Moho geometry is imaged as it deepens from ~40-km depth beneath the foothills and the Lesser Himalaya to ~58-km depth beneath the Higher Himalayan range. A midcrustal low-velocity zone is detected at ~15-km depth along ~55-km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the Main Himalayan Thrust. Our new image allows structural comparison of the Moho and of the Main Himalayan Thrust geometry along-strike of the Himalayas and documents long-wavelength lateral variations. The general crustal architecture observed on our images resembles that of Central Nepal; therefore, Western Nepal is also expected to be able to host large (M W > 8) megathrust earthquakes, as the 1505 CE event. Plain Language Summary We investigate the Earth's crust in Western Nepal. We use 16 stations to detect waves from faraway earthquakes, and using these we make an image of the structure of the crust. We find that the crust is getting thicker beneath the Himalaya and that fluids are locally present in the upper part of the crust. As this image is similar to the one we know in Central Nepal, where major earthquakes happened, it is possible that major earthquakes will also happen in Western Nepal in the future (without knowing when).
Published: 2019
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8. Anomalous V p / V s Ratios at Seismic Frequencies Might Evidence Highly Damaged Rocks in Subduction Zones

Author: Lucas Pimienta, Alexandre Schubnel, Marie Violay, Jérôme Fortin, Yves Guéguen, Hélène Lyon‐Caen, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences
Abstract: International audience; Unusually high compressional (P) to shear (S) wave velocity ratios (V p /V s) were measured at different subduction zones and interpreted as fluid-pressurized regions. Because no laboratory data reported such high values in isotropic rocks, mineralogical or anisotropic constrains were assumed. However, fluid-saturated rocks' V p /V s is a frequency-dependent property so that standard laboratory measurements cannot be directly upscaled to the field. Using a new methodology, we measured the property in the elastic regime relevant to field measurements for diverse lithologies. We obtained extreme V p /V s values, consistent with those reported at seismic frequency in the field. Consistently with a model, it shows that if high fluid pressure is a key factor, anomalous V p /V s values could evidence intense degrees of microfracturation in isotropic rocks, whichever its mineralogical content. The permeability of these regions could be larger than 10 À16 m 2. Plain Language Summary Anomalous seismic properties measured at subduction zones across the globe have been linked to the occurrence of earthquakes or tremors. However, different physical causes were postulated to interpret such seismic properties, and none of the laboratory measurements quantitatively fitted with those anomalous values. From laboratory measurements dedicated to link with field ones, we report the first data set that fits with field measurements observed at subduction zones. We show that such values might evidence a large degree of microfracturing, opened by high pore fluid pressure, in isotropic rocks of any mineralogy.
Published: 2018
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9. GPS constraints on deformation in northern Central America from 1999 to 2017, Part 1 – Time-dependent modelling of large regional earthquakes and their post-seismic effects

Author: Hélène Lyon-Caen, Douglas Hernández, Vladimir Kostoglodov, Manuel Rodriguez Maradiaga, Pierre Briole, Alejandra Staller, S. E. Graham, A. P. Ellis, Omar Flores, Niel Lord, Robert McCaffrey, Marco Guzmán-Speziale, E. Molina, Peter LaFemina, Robert D. Rogers, Cécile Lasserre, Charles DeMets, Jeffrey Rivera, Beatriz Cosenza, Department of Geosciences, University of Wisconsin-Madison, Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Universidad San Carlos, Department of Environmental, Earth and Ocean Sciences [Boston] (EEOS), University of Massachusetts [Boston] (UMass Boston), University of Massachusetts System (UMASS)-University of Massachusetts System (UMASS), Centro de Geociencias [Queretaro], Universidad Nacional Autónoma de México (UNAM), Instituto de Geofísica, Pennsylvania State University (Penn State), Penn State System-Penn State System, Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF), Universidad Nacional Autónoma de Honduras, Department of Geology [Portland], Portland State University [Portland] (PSU), Universidad Mariano Galvez, California State University [Stanislaus], Universidad Politécnica de Madrid (UPM), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Universidad Nacional Autónoma de Honduras (UNAH), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM), and Penn State Department of Geosciences
Subjects: 010504 meteorology & atmospheric sciences, Satellite geodesy, Space geodetic surveys, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Earthquake prediction, Slip (materials science), 010502 geochemistry & geophysics, 01 natural sciences, Mantle (geology), Geochemistry and Petrology, Middle america, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, Seismic cycle, business.industry, Geodetic datum, Central America, Geodesy, Geophysics, Transient deformation, Trench, Global Positioning System, business, Geology
Abstract: International audience; We use continuous and campaign measurements from 215 GPS sites in northern Central America and southern Mexico to estimate coseismic and afterslip solutions for the 2009 M w = 7.3 Swan Islands fault strike-slip earthquake and the 2012 M w = 7.3 El Salvador and M w = 7.4 Guatemala thrust-faulting earthquakes on the Middle America trench. Our simultaneous , time-dependent inversion of more than 350 000 daily GPS site positions gives the first jointly consistent estimates of the coseismic slips for all three earthquakes, their combined time-dependent post-seismic effects and secular station velocities corrected for both the co-seismic and post-seismic deformation. Our geodetic slip solutions for all three earthquakes agree with previous estimates that were derived via static coseismic-offset modelling. Our time-dependent model, which attributes all transient post-seismic deformation to earthquake afterslip, fits nearly all of the continuous GPS site position time-series within their several-millimetre position noise. Afterslip moments for the three earthquakes range from 35 to 140 per cent of the geodetic coseismic moments, with the largest afterslip estimated for the 2012 El Salvador earthquake along the weakly coupled El Salvador trench segment. Forward modelling of viscoelastic deformation triggered by all three earthquakes for a range of assumed mantle and lower crustal viscosities suggests that it accounts for under 20 per cent of the observed post-seismic deformation and possibly under 10 per cent. Our results thus point to afterslip as the primary and perhaps dominant mode of post-seismic deformation for these C The Author(s)
Published: 2018
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10. Lateral variations of the midcrustal seismicity in western Nepal: Seismotectonic implications

Author: A. Benoit, Bharat Prasad Koirala, R. Hoste-Colomer, Jean Letort, Ratna Mani Gupta, Mukunda Bhattarai, K. Maharjan, Laurent Bollinger, Chintan Timsina, Hélène Lyon-Caen, T. Kandel, L. B. Adhikari, R. Pandey, Eric Jacques, C. Baillard, R. Matrau, DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Department of Mines and Geology, National Seismological Center, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), and Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Slip (materials science), Induced seismicity, Fault (geology), 010502 geochemistry & geophysics, Earthquake swarm, 01 natural sciences, seismic swarms, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), structural control, Thrust fault, temporary seismological network, 0105 earth and related environmental sciences, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, Himalayas, Geological structure, Geophysics, Seismic hazard, 13. Climate action, Space and Planetary Science, seismicity, Geology, Seismology
Abstract: International audience; The midcrustal seismicity along the Himalayas depicts some lateral variations. This seismicity is often related to stress build up, at depth, along the downdip extent of the fault segments producing large and great earthquakes. To better characterize these variations, we deployed the first temporary seismological network in West Nepal (HiKNet) as a complement to the Nepalese national network. We used automatic picks, manually validated, to perform absolute and relative location of the earthquakes. The resulting catalog contains 2190 local events, shallow to midcrustal (8-16 km). The comparison between the seismicity and the geologic balanced cross-sections shows that most earthquakes occur within the hanging wall of the Main Himalayan Thrust fault nearby ramps or suspected contacts between Lesser Himalayan slivers. Some of the events associated with these geological structures are clustered within weeks-long earthquake swarms with seismic envelopes migrating at 35-50 m/day. These transients are possibly related to fluid migrations or geodetically unresolved slow slip events. The lateral variations of some of the structures associated to this seismicity are likely partially controlling the extent of the coseismic ruptures during intermediate earthquakes that break partly the locked fault zone, in a similar way to what was reported after the Mw7.8 2015 Gorkha-Nepal earthquake. A better characterization of the faults segmentation, including a better location and extent of the seismogenic segments at depth, is an important input for seismic hazard studies.
Published: 2018
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11. Dynamics of microseismicity and its relationship with the active structures in the western Corinth Rift (Greece)

Author: Sophie Lambotte, Anne Deschamps, Clara Duverger, Pascal Bernard, Hélène Lyon-Caen, Alexandre Nercessian, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), CRLNET, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris)
Subjects: geography, geography.geographical_feature_category, Rift, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Seismic migration, Crust, Slip (materials science), Active fault, Induced seismicity, Fault (geology), Seismicity and tectonics, 010502 geochemistry & geophysics, 01 natural sciences, Europe, Earthquake dynamics, Geophysics, Transient deformation, Geochemistry and Petrology, Geology, Seismology, 0105 earth and related environmental sciences, Asperity (materials science)
Abstract: International audience; We analyse the complete earthquake archive of the western Corinth Rift using both cross-correlations between pairs of event waveforms and accurate differential traveltimes observed at common stations, in order to identify small-scale fault structures at depth. The waveform database was generated by the dense Corinth Rift Laboratory network and includes about 205 000 events between 2000 and 2015. Half of them are accurately relocated using double-difference techniques. The novelty of this relocated catalogue is the integration of the recent westernmost earthquakes due to the extension of the network in 2010 to the western extremity of the Corinth Rift and the consideration of the whole database over more than 15 yr. The total relocated seismicity exhibits well-defined clusters at the root of the main normal faults mainly between 5 and 10 km depth in the middle of the gulf and illuminates thin active structure planes dipping north about 20° under the northern coast. Some seismicity is observed in the footwall of the main active faults, along the West and East Helike faults. We also built a multiplet database based on waveform similarity taking into account cross-correlation coefficients weighted by signal-to-noise ratios. Short-term multiplets are concentrated in the middle of the gulf along the Kamarai fault system, in a 1–2 km thick layer at 6–8 km depth, interpreted as a highly fractured geological layer. They are often associated to slow seismic migration velocities occurring in this zone during strong swarm episodes and are thus likely to be triggered by pore pressure variations. On the other hand, most long-term and regular multiplets are located deeper (7–10 km), under the northern coast, within a layer less than 0.3 km thick. They occur at the border of nearly planar structures with low seismicity rate, which we identify as fault planes, and they may be explained by aseismic slip on the fault surface around them. This supports the existence of an immature structure growing downdip towards the north at the base of the active geological layer, which possibly connects to the ductile middle crust around 15 km depth, as suggested by the occurrence of deeper events in the continuity of the 1995–fault plane. The different migration velocities (from 0.05 km d−1 to several km d−1) highlighted during the western 2014–swarms indicate that both pore pressure and creep diffusion are operating in the fault zone. The fast migrations observed in the Psathopyrgos fault zone, where a slow slip event was detected by dilatometers in 2002, compare with that for creeping faults. To the west, from spatial distribution of events, we show that the Rion–Patras fault connecting the western extremity of the Corinth Rift fault system to the Patras Rift, is dipping around 60° north–west with a rake angle of −115°. Finally, we identified two new areas within the central active zone which may correspond to large scale, locked asperities on active fault surfaces, similar in size to the main asperity broken during the 1995, MW 6.3, Aigion earthquake.
Published: 2018
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12. Large Eighteenth–Nineteenth Century Earthquakes in Western Gulf of Corinth with Reappraised Size and Location

Author: Paola Albini, Oona Scotti, Andrea Rovida, Hélène Lyon-Caen, Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Milano (INGV), Istituto Nazionale di Geofisica e Vulcanologia, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
Subjects: 021110 strategic, defence & security studies, Achaea, Rift, biology, Earthquake prediction, 0211 other engineering and technologies, Magnitude (mathematics), Context (language use), 02 engineering and technology, 010502 geochemistry & geophysics, Earthquake swarm, biology.organism_classification, 01 natural sciences, dissemin, Geophysics, European Macroseismic Scale, Geochemistry and Petrology, [SDU]Sciences of the Universe [physics], [SHS.ENVIR]Humanities and Social Sciences/Environmental studies, Mainland, Geology, Seismology, 0105 earth and related environmental sciences
Abstract: The area of the western Gulf of Corinth around the city of Aigio (Achaea, northwest Peloponnese, Greece) represents an international pilot site for continuous monitoring and multidisciplinary research on earthquake processes. In the framework of the ANR‐SISCOR Corinth Rift Laboratory project (2011–2014), a thorough reappraisal of the five largest ( M w >6) eighteenth–nineteenth century earthquakes was performed, namely those of 14 May 1748, 23 August 1817, 26 December 1861, 9 September 1888, and 25 August 1889. Written observations of earthquake effects were looked into in their original version and language and were placed in the context from which they originated, to avoid the translations and digests on which previous seismological studies had relied. Earthquake records were traced for 108 different localities, and 143 macroseismic intensities in European Macroseismic Scale 1998 (EMS‐98) have been assigned. Earthquake‐related geological phenomena have been identified and carefully mapped, to be used as a further constraint of the location and magnitude of the associated earthquakes. Finally, new parameters for the studied earthquakes have been assessed with two separate and independent strategies to quantify epistemic uncertainties. In conclusion, the 1748, 1817, and 1888 earthquakes were located in the area of Aigio; the 1861 earthquake is reckoned to be the largest in the area, with an epicentral location at sea; whereas the 1889 earthquake has been relocated to the northwest in mainland Greece, well outside the Gulf of Corinth. Electronic Supplement: Additional material and intensity values in European Macroseismic Scale 1998 (EMS‐98) for the five studied earthquakes, and tests on deriving earthquake parameters.
Published: 2017
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13. Methodology for earthquake rupture rate estimates of fault networks: example for the western Corinth rift, Greece

Author: Thomas Chartier, Oona Scotti, Hélène Lyon-Caen, Aurélien Boiselet, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
Subjects: 010504 meteorology & atmospheric sciences, Greece, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Fault networks, Corinth rift, 010502 geochemistry & geophysics, 01 natural sciences, 0105 earth and related environmental sciences, Seismic hazard assessment
Abstract: International audience; Modeling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (fault-to-fault, FtF, ruptures). The Uniform California Earthquake Rupture Forecast version 3 (UCERF-3) model takes into account this possibility by considering a system-level approach rather than an individual-fault-level approach using the geological, seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information along fault networks is often not well constrained. There is therefore a need to propose a methodology relying on geological information alone to compute earthquake rates of the faults in the network. In the proposed methodology, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty, similarly to UCERF-3. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an a priori chosen shape and the rate of earthquakes on each fault is determined by the specific slip rate of each segment depending on the possible FtF ruptures. The modeled earthquake rates are then compared to the available independent data (geodetical, seismological and paleoseis-mological data) in order to weight different hypothesis explored in a logic tree. The methodology is tested on the western Corinth rift (WCR), Greece, where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ∼ 15 mm yr −1 north–south extension. Modeling results show that geological, seismological and paleoseismological rates of earthquakes cannot be reconciled with only single-fault-rupture scenarios and require hypothesizing a large spectrum of possible FtF rupture sets. In order to fit the imposed regional Gutenberg–Richter (GR) MFD target, some of the slip along certain faults needs to be accommodated either with interseismic creep or as post-seismic processes. Furthermore, computed individual faults' MFDs differ depending on the position of each fault in the system and the possible FtF ruptures associated with the fault. Finally, a comparison of modeled earthquake rupture rates with those deduced from the regional and local earthquake catalog statistics and local paleoseismological data indicates a better fit with the FtF rupture set constructed with a distance criteria based on 5 km rather than 3 km, suggesting a high connectivity of faults in the WCR fault system.
Published: 2017
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14. Automatic analysis of the Gorkha earthquake aftershock sequence: evidences of structurally segmented seismicity

Author: Hélène Lyon-Caen, Andreas Rietbrock, L. B. Adhikari, Laurent Bollinger, C. Baillard, Jean Letort, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), University of Liverpool, Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Department of Mines and Geology, National Seismological Center, Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL)
Subjects: Seismic gap, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, Asia, 010504 meteorology & atmospheric sciences, Earthquake source observations, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Slip (materials science), Induced seismicity, Crustal structure, Seismicity and tectonics, 010502 geochemistry & geophysics, 01 natural sciences, Computational seismology, Tectonics, Geophysics, Geochemistry and Petrology, Attenuation law, Shear zone, Geology, Aftershock, Seismology, 0105 earth and related environmental sciences
Abstract: International audience; We present the first 3 months of aftershock activity following the 2015 April 25 Gorkha earthquake M w 7.8 recorded on the Nepalese Seismic network. We deployed an automatic procedure composed of three main stages: (1) coarse determination of the P and S onsets; (2) phase association to declare events and (3) iterative addition and refinement of onsets using the Kurtosis characteristic function. In total 9188 events could be located in the Kathmandu region with the majority having small location errors (
Published: 2017
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15. Investigating Dynamic Triggering of Seismicity by Regional Earthquakes: The Case of the Corinth Rift (Greece)

Author: Anthony Sladen, Anne Deschamps, N. Voulgaris, Hélène Lyon-Caen, Louis De Barros, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens = University of Athens (NKUA | UoA), CRLNET, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), National and Kapodistrian University of Athens (NKUA), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris)
Subjects: Rift, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Magnitude (mathematics), Geophysics, Induced seismicity, 010502 geochemistry & geophysics, 01 natural sciences, Seismic wave, 13. Climate action, General Earth and Planetary Sciences, Geology, Seismology, 0105 earth and related environmental sciences
Abstract: International audience; Dynamic triggering has been commonly observed after large teleseismic events, but the physics behind it is still under debate. To broaden observations, we here focus on the dynamic triggering by regional earthquakes, that is, by events with magnitude lower than 6.2 at distances smaller than 600 km. The western part of the Corinth Rift (Greece) is characterized by intense seismic swarms and is therefore adapted to study such responses. The microseismicity rates before and after the transient perturbations are high enough to analyze 30 regional earthquakes out of the 59 occurring in 2013. More than 40% of those 30 events, including earthquakes with magnitude as small as 4.5, are associated with a significant seismicity rate increase. The triggerability primarily depends on the amplitude of the seismic waves. However, triggering is mainly observed when the seismic perturbations are orthogonal to the faults, which suggests that fluid pressurization is likely involved.
Published: 2017
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16. Lateral structure variations and transient swarm revealed by seismicity along the Main Himalayan Thrust north of Kathmandu

Author: A. Burtin, Hélène Lyon-Caen, R. Hoste-Colomer, L. B. Adhikari, Laurent Bollinger, DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), National Seismological Centre, Katmandhu, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), and Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Seismicity, Swarm behaviour, Thrust, Time sequence, Fault (geology), Induced seismicity, 010502 geochemistry & geophysics, 01 natural sciences, Stress field, Geophysics, Transition zone, Main Himalayan Thrust, Transient (oscillation), Relative relocation, Fault segmentation, Seismology, Geology, 0105 earth and related environmental sciences, Earth-Surface Processes
Abstract: International audience; The midcrustal seismicity along the Main Himalayan Thrust in Nepal presents lateral variations along the rupture of the 2015 Gorkha earthquake. In order to resolve these variations, we relocate the seismicity north of Kathman-du, during a period well covered by the Nepal National Seismological Network, using a double-difference algorithm. The 550 relocated events highlight a complex pattern of clustered seismicity within the unstable-stable transition zone. Part of the seismicity is densely clustered on a southward dipping plane which ruptured on Jan-uary 31st 1997 (ML = 5.8), activating a backthrust with a geometry consistent with the centroid moment tensor of this event calculated in this study. At its eastern end, the midcrustal cluster is offset by 20 km to the south suggesting the presence of a tear fault. The analysis of the time sequence allows constraining a scenario involving stress transfer between these local midcrustal structures, beginning more than one month before the 1997 main shock. The temporal evolution of the seismicity is strikingly similar for two other transient seismic swarm episodes which developed hundreds of kilometers apart along the Main Himalayan Thrust at the same time. The local stress field appears responsible for the higher sensitivity of these regions to subtle strain transients developing along the Main Himalayan Thrust.
Published: 2017
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17. Ambient noise tomography of the western Corinth Rift, Greece

Author: Pascal Bernard, Efthimios Sokos, Dimitrios Giannopoulos, Anne Deschamps, Paraskevas Paraskevopoulos, G-Akis Tselentis, Aurélien Mordret, Diane Rivet, Hélène Lyon-Caen, Patras Seismological Laboratory, University of Patras [Greece], Géoazur (GEOAZUR 7329), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Massachusetts Institute of Technology (MIT), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), National Observatory of Athens (NOA), CRLNET, University of Patras, Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), and Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
Subjects: Rift, Seismic tomography, 010504 meteorology & atmospheric sciences, Passive seismic tomography, Corinth, Ambient noise level, Seismic interferometry, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Crustal structure, 010502 geochemistry & geophysics, 01 natural sciences, Tectonics, Geophysics, Basement (geology), Interferometry, Geochemistry and Petrology, Ambient noise tomography, Group velocity, Spatial variability, Corinth Rift, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: International audience; Three years of continuous waveform data recorded at 22 stations from the Corinth Rift Laboratory and the Hellenic Unified Seismological Network are used to perform an ambient noise surface-wave tomography of the western Corinth Rift. All available vertical component time-series were cross-correlated to extract empirical Rayleigh-wave Green's functions. Group velocity dispersion curves were measured for each station-pair by applying frequency-time analysis and then inverted to build 2D group velocity maps between 1 and 6 s period. Finally, we locally inverted these velocity maps using a neighborhood algorithm to assess the 3D shear-velocity model of the shallow crustal structure of the western Corinth Rift. Across all studied periods the southern coast of the Corinth Gulf is generally imaged as a region of lower velocities compared to the northern coast. At periods up to 3 s, the spatial variation of the group velocities is correlated with the surface geology of the area. Lower velocities are observed in areas where mostly Plio-Quaternary syn-rift sediments are present, such as off-shore regions of the rift, the Mornos delta and the largest part of the southern coast. Higher velocities are observed in pre-rift basement structures which are dominated mostly by carbonates. At periods above 3 s, where Rayleigh-waves begin to sense deeper structures below the sediments within the underlying basement, our study highlights the presence of a distinct zone of lower velocities across the southern part of the rift with an elongation in the WNW-ESE direction. The interpretation of this low velocity includes two arguments, the present-day active tectonic regime and the possible involvement of fluids circulation processes at depth within a highly fractured upper crust in the vicinity of the major faults zones. In general, the results demonstrate good agreement with the major geological and tectonic features of the area, as well as with previous local earthquake tomography studies and support the assumption of fluid circulations at depth. This work intends to be the base for further investigations towards the study of the Corinth Rift structure using long-time series of ambient noise data.
Published: 2017
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18. Teleseismic depth estimation of the 2015 Gorkha−Nepal aftershocks

Author: Aurélie Guilhem, Laurent Bollinger, Jean Letort, C. Baillard, L. B. Adhikari, Yoann Cano, Hélène Lyon-Caen, Institut des Sciences de la Terre, Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), DAM Île-de-France (DAM/DIF), Direction des Applications Militaires (DAM), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Department of Mines and Geology, National Seismological Center, Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris)
Subjects: Estimation, 010504 meteorology & atmospheric sciences, Earthquake source observations, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Body waves, Seismicity and tectonics, 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, Geochemistry and Petrology, Receiver function, Seismology, Aftershock, Geology, 0105 earth and related environmental sciences
Abstract: International audience; The depth of 61 aftershocks of the 2015 April 25 Gorkha, Nepal earthquake, that occurred within the first 20 d following the main shock, is constrained using time delays between teleseismic P phases and depth phases (pP and sP). The detection and identification of these phases are automatically processed using the cepstral method developed by Letort et al., and are validated with computed radiation patterns from the most probable focal mechanisms. The events are found to be relatively shallow (13.1 ± 3.9 km). Because depth estimations could potentially be biased by the method, velocity model or selected data, we also evaluate the depth resolution of the events from local catalogues by extracting 138 events with assumed well-constrained depth estimations. Comparison between the teleseismic depths and the depths from local and regional catalogues helps decrease epistemic uncertainties, and shows that the seismicity is clustered in a narrow band between 10 and 15 km depth. Given the geometry and depth of the major tectonic structures, most aftershocks are probably located in the immediate vicinity of the Main Himalayan Thrust (MHT) shear zone. The mid-crustal ramp of the flat/ramp MHT system is not resolved indicating that its height is moderate (less than 5−10 km) in the trace of the sections that ruptured on April 25. However, the seismicity depth range widens and deepens through an adjacent section to the east, a region that failed on 2015 May 12 during an M w 7.3 earthquake. This deeper seismicity could reflect a step-down of the basal detachment of the MHT, a lateral structural variation which probably acted as a barrier to the dynamic rupture propagation.
Published: 2016
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19. 3D imaging of the Corinth rift from a new passive seismic tomography and receiver function analysis

Author: Maxime Godano, Alexandrine Gesret, Mark Noble, Hélène Lyon-Caen, Stéphanie Gautier, Anne Deschamps, Centre de Géosciences (GEOSCIENCES), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Géoazur (GEOAZUR 7329), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), MINES ParisTech - École nationale supérieure des mines de Paris-PSL Research University (PSL), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Transferts en milieux poreux, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA), and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
Subjects: [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC]
Abstract: International audience; The Corinth Rift is the most seismically active zone in Europe. The area is characterized by very localized NSextension at a rate of1.5cm/year, the occurrence of frequent and intensive microseismic crises and occasionalmoderate to large earthquakes like in 1995 (Mw=6.1).Since the year 2000, the Corinth Rift Laboratory (CRL, http://crlab.eu) consisting in a multidisciplinary naturalobservatory, aims at understanding the mechanics of faulting and earthquake nucleation in the Rift. Recent studieshave improved our view about fault geometry and mechanics within CRL, but there is still a critical need for a betterknowledge of the structure at depth both for the accuracy of earthquake locations and for mechanical interpretationof the seismicity.In this project, we aim to analyze the complete seismological database (13 years of recordings) of CRL by usingrecently developed methodologies of structural imaging, in order to determine at the same time and with highresolution, the local 3D structure and the earthquake locations.We perform an iterative joint determination of 3D velocity model and earthquake coordinates. In a first step, Pand S velocity models are determined using first arrival time tomography method proposed by Taillandier et al.(2009). It consists in the minimization of the cost function between observed and theoretical arrival times which isachieved by the steepest descent method (e.g. Tarantola 1987). This latter requires computing the gradient of thecost function by using the adjoint state method (Chavent 1974). In a second step, earthquakes are located in thenew velocity model with a non-linear inversion method based on a Bayesian formulation (Gesret et al. 2015). Step1 and 2 are repeated until the cost function no longer decreases.We present preliminary results consisting in: (1) the adjustement of a 1D velocity model that is used as initialmodel of the 3D tomography and (2) a first attempt of the joint determination of 3D velocity model and earthquakelocation.In addition to the tomographic imaging, we perform a preliminary receiver function analysis of teleseismic datarecorded by the broadband stations of the CRL network. The RF analysis should provide the interface depthsbeneath seismometers and increase the imaging resolution of the upper crustal structures provided by the 3Dtomography. In this first attempt, we adjust the 1D velocity model that produces a synthetic RF as similar aspossible to the observed RF for a subset of data. We compare the identified interfaces with structures imaged bythe tomography.
Published: 2016

20. The 2003-2004 seismic swarm in the western Corinth rift: Evidence for a multiscale pore pressure diffusion process along a permeable fault system

Author: Pascal Bernard, Sophie Lambotte, M. Godano, Clara Duverger, Hélène Lyon-Caen, Département de sismologie, Institut de Physique du Globe de Paris (IPG Paris), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), CRLNET, ANR-10-BLAN-0619,SISCOR,Aléas, dynamique SISmogène, et couplages sismiques/asismiques d'un systeme de faille actives dans la région ouest du Rift de CORinthe, Grèce(2010), European Project: 282862,EC:FP7:ENV,FP7-ENV-2011,REAKT(2011), Institut de Physique du Globe de Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), and Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: 010504 meteorology & atmospheric sciences, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Fault (geology), 010502 geochemistry & geophysics, Thermal diffusivity, 01 natural sciences, Nappe, Pore water pressure, seismic swarms, pore pressure migration, Corinth Rift, microseismicity, 0105 earth and related environmental sciences, geography, Microseism, geography.geographical_feature_category, Rift, Greece, Swarm behaviour, pore pressure, Geophysics, Diffusion process, General Earth and Planetary Sciences, multiplets, permeability, Seismology, Geology
Abstract: International audience; Microseismic multiplets occurring in the western Corinth rift, Greece, during a large swarm are analyzed to retrieve their spatiotemporal characteristics. These multiplets activated small subfaults at depth (∼7 km), up to 1 km long, at the root of two parallel active normal faults. The swarm migrates westward nearly horizontally over 10 km at an average velocity of 50 m/d with a diffusivity of 0.5 m2 s−1. It successively activates the Aigion fault, a relay zone in its hanging wall, and the Fassouleika fault. Within each multiplet, hypocenters also migrate with diffusivities ranging from 0.001 to 0.4 m2 s−1. The largest internal diffusivities appear at the core of the layer defined by the clusters. These results are interpreted as a hydroshear process caused by pore pressure migration within permeable corridors resulting from the intersection of the major faults with a brittle geological layer inherited from the Hellenic nappe stack.
Published: 2015
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21. The 2013 earthquake swarm in Helike, Greece: seismic activity at the root of old normal faults

Author: Efthimios Sokos, N. Voulgaris, Anne Deschamps, Vasilis Kapetanidis, A. Serpetsidaki, Pascal Bernard, Emanuela Matrullo, George Bozionelos, George Kaviris, Panayotis Papadimitriou, A. Karakonstantis, K. Makropoulos, Hélène Lyon-Caen, Department of Geophysics and Geothermics, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Patras Seismological Laboratory, University of Patras [Greece], Seismological Laboratory, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), National and Kapodistrian University of Athens (NKUA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), University of Patras, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), University of Patras [Patras], Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), and Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: Focal mechanism, geography, geography.geographical_feature_category, Rift, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Spatial analysis, Swarm behaviour, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Slip (materials science), Induced seismicity, Fault (geology), Seismicity and tectonics, 010502 geochemistry & geophysics, Earthquake swarm, 01 natural sciences, Fourier analysis, Geophysics, Geochemistry and Petrology, Fractures and faults, Seismic moment, Dynamics: seismotectonics, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: International audience; The Corinth Rift in Central Greece has been studied extensively during the past decades, as it is one of the most seismically active regions in Europe. It is characterized by normal faulting and extension rates between 6 and 15 mm yr−1 in an approximately N10E° direction. On 2013 May 21, an earthquake swarm was initiated with a series of small events 4 km southeast of Aigion city. In the next days, the seismic activity became more intense, with outbursts of several stronger events of magnitude between 3.3 and 3.7. The seismicity migrated towards the east during June, followed by a sudden activation of the western part of the swarm on July 15th. More than 1500 events have been detected and manually analysed during the period between 2013 May 21 and August 31, using over 15 local stations in epicentral distances up to 30 km and a local velocity model determined by an error minimization method. Waveform similarity-based analysis was performed, revealing several distinct multiplets within the earthquake swarm. High-resolution relocation was applied using the double-difference algorithm HypoDD, incorporating both catalogue and cross-correlation differential traveltime data, which managed to separate the initial seismic cloud into several smaller, densely concentrated spatial clusters of strongly correlated events. Focal mechanism solutions for over 170 events were determined using P-wave first motion polarities, while regional waveform modelling was applied for the calculation of moment tensors for the 18 largest events of the sequence. Selected events belonging to common spatial groups were considered for the calculation of composite mechanisms to characterize different parts of the swarm. The solutions are mainly in agreement with the regional NNE–SSW extension, representing typical normal faulting on 30–50° north-dipping planes, while a few exhibit slip in an NNE–SSW direction, on a roughly subhorizontal plane. Moment magnitudes were calculated by spectral analysis of S waves, yielding b-values between 1.1 and 1.2 in their frequency–magnitude distribution. The seismic moment release history indicates swarm-like activity during the first phase, which could have acted as a preparatory stage for the second phase (after 12 July) that presented a more typical main-shock–aftershock behaviour. The spatiotemporal analysis reveals that the swarm has occurred in a volume that is likely related with the extension at depth of the NNE-dipping Pirgaki normal fault, outcropping ∼8 km to the south. The slow velocity of eastward migration of the epicentres during June implies triggering by fluids. The situation appears different in the second phase of the sequence, which was probably triggered by a build-up of stress during the first one. The relatively deep hypocentres of the 2013 swarm, compared to the shallower seismic layer within the rift, and their coincidence with the steeply dipping Pirgaki fault, favour an immature rift detachment model. Previous results from instrumental data indicate that approximately the same region had been activated during July–August 1991. The availability of the dense permanent seismological network data thus allowed for a detailed analysis of this crisis, a better understanding of its mechanical context and of the earlier events.
Published: 2015
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22. Geodetic slip solutions for the Mw = 7.4 Champerico (Guatemala) earthquake of 2012 November 7 and its postseismic deformation

Author: Cécile Lasserre, Enrique Molina, Charles DeMets, Hélène Lyon-Caen, A. P. Ellis, Omar Flores, N. E. Lord, Pierre Briole, Jeffrey Rivera, Dpt of Geosciences Wisconsin, University of Wisconsin-Madison, Department of Geoscience, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Universidad Mariano Galvez, Universidad de San Carlos de Guatemala, Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), and Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, Seismic cycle, 010504 meteorology & atmospheric sciences, Subduction, Satellite geodesy, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Geodetic datum, Crust, Central America, Slip (materials science), 010502 geochemistry & geophysics, Geodesy, 01 natural sciences, Mantle (geology), Geophysics, Geochemistry and Petrology, [SDU]Sciences of the Universe [physics], Epicenter, earthquake, Trench, Subduction zone processes, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: International audience; As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 2012 November 7 M w = 7.4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador and Mexico to estimate the coseismic slip and postseismic deformation of the November 2012 Champerico (Guatemala) earthquake. An inversion of the coseismic offsets, which range up to ∼47 mm at the surface near the epicentre, indicates that up to ∼2 m of coseismic slip occurred on a ∼30 × 30 km rupture area between ∼10 and 30 km depth, which is near the global CMT centroid. The geodetic moment of 13 × 10 19 N m and corresponding magnitude of 7.4 both agree well with independent seismological estimates. Transient postseismic deformation that was recorded at 11 GPS sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and/or mantle. Modelling of the viscoelastic deformation suggests that it constituted no more than ∼30 per cent of the short-term postseismic deformation. GPS observations that extend six months after the earthquake are well fit by a model in which most afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than ∼20 per cent of the coseismic moment. An independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the GPS offsets well if its slip centroid is translated ∼50 km to the west to a position close to our slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-7 m for the peak slip along a region of the interface no larger than 30 × 30 km.
Published: 2015
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23. New constraints from seismology and geodesy on the Mw = 6.4 2008 Movri (Greece) earthquake: evidence for a growing strike-slip fault system

Author: E. Sokos, G-Akis Tselentis, Hélène Lyon-Caen, S. Lambotte, Panagiotis Elias, Maya Ilieva, A. Serpetsidaki, Pascal Bernard, Anne Deschamps, Pierre Briole, Seismological Laboratory, Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), National Observatory of Athens (NOA), Bulgarian Academy of Sciences (BAS), Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Ecole et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Seismology Laboratory, University of Patras [Patras], Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), CRLNET, University of Patras, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), and Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])
Subjects: geography, geography.geographical_feature_category, Dynamics and mechanics of faulting, 010504 meteorology & atmospheric sciences, Satellite geodesy, Radar interferometry, North Anatolian Fault, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Fault (geology), Seismicity and tectonics, 010502 geochemistry & geophysics, Strike-slip tectonics, Geodesy, 01 natural sciences, Earthquake dynamics, Geophysics, Shear (geology), Geochemistry and Petrology, Seismic moment, Shear zone, Geology, Seismology, Aftershock, 0105 earth and related environmental sciences
Abstract: International audience; The 2008 Mw = 6.4 Movri earthquake ruptured a NNE right lateral strike-slip fault about 30 km south of the city of Patras. Although some strike-slip activity on minor faults was known, there was no tectonic evidence of large scale NS striking fault and such a large event was not anticipated. Following the event, a network of six stations was installed for 4 months in the epicentral area in order to monitor aftershocks and in particular the northern part of the rupture area closest to the city of Patras. We combine these new aftershock observations with GPS measurements of an already existing geodetic network in the area performed just after the earthquake, as well as with SAR interferograms, together with already published source studies, in order to refine already proposed models of this event. The combined data set allows defining much more accurately the lateral and vertical limits of the rupture. Its length inferred from geodesy is ∼15 km and its modelled upper edge ∼17 km. The seismic moment then constrains the lower edge to coincide, within a few kilometres, with the Moho interface. The absence of seismicity in the shallow crust above the co-seismic fault is interpreted as a result of the decoupling effect of possible presence of salt layers above the rupture area, near 14 to 16 km in depth, which favours our interpretation of an immature strike-slip fault system, compatible with the absence of surface ruptures. The immature character of this large crustal fault is further suggested by the high variability of focal mechanisms and of fault geometries deduced from aftershock clusters, in the strike direction. Its geometry and mechanism is consistent with the crustal shear, striking NNE, revealed by GPS in this region. This shear and faulting activity might be generated by the differential slip rate on the subduction interface, 50 km to the south, leading to a north-northeastward propagating strike-slip fault zone. The wide extension of the aftershock distribution forming a NNE alignment, beyond the rupture area towards the north, suggests a localization process of the shear strain, which could be the preliminary stage of fault propagation further to the NNE. An alternative speculative model for this regional stress could be the existence of a well-developed NNE striking shear zone within the uppermost mantle, marking at depth the southward propagation of the northern branch of the North Anatolian fault. Both models may not be exclusive of each other, and in fact their sources may be mechanically interdependent.
Published: 2014
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24. Reassessment of the rifting process in the Western Corinth Rift from relocated seismicity

Author: Mélanie Drilleau, G. Patau, Anne Deschamps, Seid Bourouis, Petra Adamová, Franchesco Pacchiani, Pascal Bernard, S. Lambotte, Alexandre Nercessian, Hélène Lyon-Caen, Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Département de sismologie (DS (UMR_7580)), IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Centre de Recherche en Astronomie Astrophysique et Géophysique (CRAAG), CRLNET, ANR-10-BLAN-0619,SISCOR,Aléas, dynamique SISmogène, et couplages sismiques/asismiques d'un systeme de faille actives dans la région ouest du Rift de CORinthe, Grèce(2010), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire de géologie de l'ENS (LGENS), Institut de Physique du Globe de Paris (IPGP), and Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, Rift, Dynamics and mechanics of faulting, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Continental tectonics: extensional, Crust, Active fault, Induced seismicity, Fault (geology), Geneva, Seismicity and tectonics, 010502 geochemistry & geophysics, Blind thrust earthquake, 01 natural sciences, Pore water pressure, Geophysics, Geochemistry and Petrology, Submarine pipeline, Geology, Seismology, Switzerland, 0105 earth and related environmental sciences
Abstract: International audience; The seismic activity in the western part of the Corinth Rift (Greece) over the period 2000– 2007, monitored by a dense network of three-component stations, is analysed in terms of multiplets and high precision relocation using double difference techniques. This detailed analysis provides new insights into the geometry of faults at depth, the nature and the structure of the active zone at 6–8 km depth previously interpreted as a possible detachment, and more generally into the rifting process. The seismicity exhibits a complex structure, strongly varying along the rift axis. The detailed picture of the seismic zone below the rift indicates that its shallower part (at depths of 6–8 km) is 1–1.5 km thick with a complex microstructure, and that its deeper part (at depths of 9–12 km) gently dipping to the north (10–20°) is 0.1–0.3 km thick with a microstructure consistent with the general slope of the structure. Although the nature of this seismic zone remains an open question, the presence of seismicity beneath the main active area, the strong variability of the structure along the rift over short distances and the complex microstructure of the shallower part revealed by the multiplet analysis are arguments against the hypothesis of a mature detachment under the rift: this active zone more likely represents a layer of diffuse deformation. The geometry of the mapped active faults is not well defined at depth, as no seismicity is observed between 0 and 4 km, except for the Aigion Fault rooting in the seismic layer at 6 km depth with a dip of 60°. A distinct cloud of seismicity may be associated with the antithetic Kalithea Fault, on which the 1909 Fokis earthquake (M s = 6.3) may have occurred. The link between the 1995 rupture (M s = 6.2) and the faults known at the surface has been better constrained, as the relocated seismicity favours a rupture on an offshore, blind fault dipping at 30° , rather than on the deeper part of the East Helike Fault. Consequently, the 1995 event is expected to have decreased the Coulomb stress on the East Helike Fault. To explain these seismic observations along with the geodetic observations, a new mechanical model for the rifting process in this region is proposed, involving non-elastic, mostly aseismic uniform NS opening below the rift axis, coupled with the downward and northward growth of a yet immature detachment: the reported GPS rates would mainly result from this deep, silent source, and the seismicity would reveal the detachment position, not yet connected to the ductile lower crust. In such a model, the strong fluctuations of microseismicity would result from small strain instabilities, undetected by continuous GPS and possibly related to pore pressure transients.
Published: 2014
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25. Focal mechanisms of earthquake multiplets in the western part of the Corinth Rift (Greece): influence of the velocity model and constraints on the geometry of the active faults

Author: Maxime Godano, F. Pacchiani, Pascal Bernard, Hélène Lyon-Caen, Anne Deschamps, S. Lambotte, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), CRLNET, ANR-10-BLAN-0619,SISCOR,Aléas, dynamique SISmogène, et couplages sismiques/asismiques d'un systeme de faille actives dans la région ouest du Rift de CORinthe, Grèce(2010), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Centre de Géosciences (GEOSCIENCES), MINES ParisTech - École nationale supérieure des mines de Paris-PSL Research University (PSL), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de géologie de l'ENS (LGE), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Laboratoire de Sismologie (IPGP), Institut de Physique du Globe de Paris, Université Jean Moulin - Lyon 3 (UJML), Université de Lyon, Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)
Subjects: geography, geography.geographical_feature_category, Rift, Plane (geometry), Earthquake source observations, Continental tectonics: extensional, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Geometry, Active fault, Fault (geology), Seismicity and tectonics, Extensional definition, Tectonics, Geophysics, Amplitude, Fractures and faults, Geochemistry and Petrology, Submarine pipeline, Dynamics: seismotectonics, Seismology, Geology
Abstract: International audience; The composite fault plane solutions for 24 large multiplets recorded in the western part of the Corinth Rift between 2000 and 2007 are computed by jointly inverting P polarities and Sv/P, Sh/P, Sv/Sh amplitude ratios of the direct waves. The fault plane solutions are determined using 1-D and 3-D velocity models. Solutions computed with the 3-D velocity model are preferred to the ones computed with the 1-D model because overall, 3-D solutions have a better score function. They correspond essentially to E–NE/W–SW and W–NW/E–SE striking normal faults, which is consistent with the N–S extensional/vertical shortening tectonic regime of the area. For 15 multiplets, one of the nodal planes is similar to the plane delineated by the earthquakes. It is then possible to determine which nodal plane is the fault plane. The analysis of the fault plane solutions highlights a clear decrease of their dip with depth and towards the north. Several multiplets with steeply dipping fault planes (50°–60°) located at depths of 7–8 km are clearly located at the base of onshore and offshore faults that crop out close to the south border of the Corinth Gulf, indicating that these faults are steep down to 7–8 km depth. To the north, multiplets underline a low angle north-dipping structure (20°–30°) on which steep north-dipping faults could take root.
Published: 2014
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26. Coseismic velocity variations caused by static stress changes associated with the 2001 Mw=4.3 Agios Ioanis earthquake in the Gulf of Corinth, Greece

Author: L. Cociani, Anne Deschamps, F. Pacchiani, Christopher J. Bean, Hélène Lyon-Caen, Seismology and Computational Rock Physics Laboratory, School of Geological Sciences [Dublin], University College Dublin [Dublin] (UCD)-University College Dublin [Dublin] (UCD), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Soil Science, Aquatic Science, 010502 geochemistry & geophysics, Oceanography, Spatial distribution, 01 natural sciences, Coda, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), medicine, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Shore, geography, geography.geographical_feature_category, Ecology, Paleontology, Stiffness, Forestry, Crust, In situ stress, Perturbation (geology), Geophysics, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Static stress, medicine.symptom, Geology, Seismology
Abstract: [1] The analysis of temporal variations in the seismic velocity across faults can be used to estimate in situ stress changes. Seismic velocity of propagation depends on the fault stiffness, which is a function of stress. The coda wave interferometry technique is applied to seven families of repeating earthquakes (multiplets) recorded on the southern shore of the Gulf of Corinth, Greece, to estimate high precision velocity changes in the Earth's crust associated with the Mw = 4.3 Agios Ioanis earthquake. Results show that the Agios Ioanis event causes a perturbation in elastic properties at seismogenic depth, resulting in a reduction of 0.2% in the seismic velocity. The results are not consistent with either damage induced by dynamic stresses nor a fluid transient origin. In contrast, both the spatial distribution and magnitude of the velocity perturbation correlate well with modeled static stress variations. This suggests that the measured changes in the mechanical properties of the seismogenic crust can be attributed to a change in static stress field associated with the Mw = 4.3 Agios Ioanis earthquake. The velocity changes indicate an unclamping of the Pyrgaki fault at depth, which has local hazard implications.
Published: 2010
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27. Seismicity and Crustal Structure of the Polochic-Motagua Fault System Area (Guatemala)

Author: A. Nercessian, O. Flores, Hélène Lyon-Caen, S. Cortez, E. Molina, J. Requenna, A. Franco, T. Monfret, Jérôme Vergne, D. Monterosso, Géoazur (GEOAZUR 6526), Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, Crust, Slip (materials science), Induced seismicity, 010502 geochemistry & geophysics, 01 natural sciences, Graben, Geophysics, Discontinuity (geotechnical engineering), Lithosphere, Receiver function, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: We report results from a six-month seismological experiment in the area of the eastern Polochic-Motagua fault system (Guatemala) designed to both characterize the present seismicity and bring some constraints on the lithospheric structure. The seismic activity occurs in the upper 15 km of the crust, on the Polochic and the Motagua faults as well as in a NS-trending graben south of the Motagua fault and within the active folds north of the Polochic fault. From receiver function analysis the Moho discontinuity is found at about 35 km depth north of the Polochic fault and south of the Motagua fault, while the region in between is characterized by a 4-to-6-km thinner crust or by a 6–7% decrease of the Vp / Vs ratio. The more than 2,000-km-long, mostly submarine, left-lateral strike-slip boundary between the North American and the Caribbean plates continues on land with the Polochic-Motagua fault system mainly located in Guatemala (Figure 1). This fault system accommodates 20 mm/yr of left lateral strike-slip movement ( e.g. , Lyon-Caen et al. 2006) and includes three major convex subparallel EW-trending faults which are, from north to south, the Polochic, the Motagua, and the Jocotan. Both the Polochic and Motagua faults show evidence of recent activity in their historical seismicity (Table 1; and see also Carr and Stoiber 1977; White and Harlow 1993; Ambraseys and Adams 2001) and their morphology ( e.g. , Burkart and Self 1985, Schwartz et al. 1979). South of the Motagua fault, a series of NS-trending grabens extends from the Honduras depression on the Caribbean Coast of Honduras to the Guatemala graben in the center of Guatemala. The last large earthquake ( Mw ∼7.5) in Guatemala occurred in February 1976, ruptured 230 km of the Motagua fault with an average slip observed at the surface of 1.4 m …
Published: 2009
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28. The Western Gulf of Corinth (Greece) 2020–2021 Seismic Crisis and Cascading Events: First Results from the Corinth Rift Laboratory Network

Author: George Kaviris, Panagiotis Elias, Vasilis Kapetanidis, Anna Serpetsidaki, Andreas Karakonstantis, Vladimír Plicka, Louis De Barros, Efthimios Sokos, Ioannis Kassaras, Vassilis Sakkas, Ioannis Spingos, Sophie Lambotte, Clara Duverger, Olivier Lengliné, Christos P. Evangelidis, Ioannis Fountoulakis, Olga-Joan Ktenidou, František Gallovič, Simon Bufféral, Emilie Klein, El Madani Aissaoui, Oona Scotti, Helene Lyon‐Caen, Alexis Rigo, Panayotis Papadimitriou, Nicholas Voulgaris, Jiri Zahradnik, Anne Deschamps, Pierre Briole, and Pascal Bernard
Subjects: Geology, QE1-996.5
Abstract: We investigate a seismic crisis that occurred in the western Gulf of Corinth (Greece) between December 2020 and February 2021. This area is the main focus of the Corinth Rift Laboratory (CRL) network, and has been closely monitored with local seismological and geodetic networks for 20 yr. The 2020–2021 seismic crisis evolved in three stages: It started with an Mw 4.6 event near the northern shore of the Gulf, opposite of Aigion, then migrated eastward toward Trizonia Island after an Mw 5.0 event, and eventually culminated with an Mw 5.3 event, ∼3 km northeast of the Psathopyrgos fault. Aftershocks gradually migrated westward, triggering another cluster near the junction with the Rion–Patras fault. Moment tensor inversion revealed mainly normal faulting; however, some strike-slip mechanisms also exist, composing a complex tectonic regime in this region dominated by east–west normal faults. We employ seismic and geodetic observations to constrain the geometry and kinematics of the structures that hosted the major events. We discuss possible triggering mechanisms of the second and third stages of the sequence, including fluids migration and aseismic creep, and propose potential implications of the Mw 5.3 mainshock for the seismic hazard of the region.
Published: 2021
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29. A layered model of the upper crust in the Aigion region of Greece, inferred from arrival times of the 2001 earthquake sequence

Author: Vladimír Plicka, Jaromír Janský, Oldřich Novotný, Hélène Lyon-Caen, Department of Geophysics, Faculty of Mathematics and Physics, Charles University [Prague] (CU), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), and CRLNET
Subjects: Rift, 010504 meteorology & atmospheric sciences, Greece, Layered model, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Active fault, 010502 geochemistry & geophysics, 01 natural sciences, conjugate gradients, crustal structure, 1-D model, Sequence (geology), Geophysics, Seismic hazard, Geochemistry and Petrology, Passive seismic, Gulf of Corinth, arrival times, Upper crust, Structural geology, Geology, Seismology, 0105 earth and related environmental sciences
Abstract: International audience; The western part of the Gulf of Corinth attracts attention due to its seismically active fault system and considerable seismic hazard. Detailed studies of the seismic activity of the region have been carried out especially as part of the so-called Corinth Rift Laboratory (CRL) Project. For standard earthquake locations, the CRL uses the HYPO algorithm and a special structural model that is composed of homogeneous layers (Rigo et al., 1996). This model was derived from a passive seismic experiment in a broader area around the western part of the Gulf. A significant part of the seismic activity is concentrated close to the town of Aigion, which was damaged by a strong earthquake in 1995. A sequence of smaller earthquakes occurred to the south of this town in the year 2001. In the present paper, we have used this sequence to derive an improved structural model for the region in the vicinity of the town of Aigion. This new model is based on the minimization of travel-time residuals. In particular, we used arrival times from a subset of 88 events recorded by at least 5 stations of the southern part of the CRL network, had magnitudes of over 2.3, and were recorded at the nearest station (station code AIO). A variant of the method of conjugate gradients has been used for this purpose. In comparison with the model derived by Rigo et al. (1996), the new model is characterized by a higher νP/νS velocity ratio and by higher velocities to a depth of about 7 km. The new model was derived with the aim to get more accurate locations of future events in the vicinity of the town of Aigion
Published: 2007
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30. Kinematics of the North American–Caribbean-Cocos plates in Central America from new GPS measurements across the Polochic-Motagua fault system

Author: O. Porras, Eric Barrier, L. Chiquin, Cécile Lasserre, E. Molina, I. Arzu, A. Franco, Omar Flores, T. Duquesnoy, J. Requena, Hélène Lyon-Caen, R. Wolf, O. Galicia, M. Chiquin, J. Luna, V. Robles, J. Romero, Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Laboratoire de tectonique (LT), Centre National de la Recherche Scientifique (CNRS)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Laboratoire Central des Ponts et Chaussées (LCPC)-Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Centro Universitario del Norte, Universidad de San Carlos de Guatemala, Centro de Estudios Superiores de Energia y Minas, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia y Hidrologia (INSIVUMEH) (INSIVUMEH), INSIVUMEH, Department of Molecular Biology, Faculty of Biology, Campus Vegazana s/n, University of Leon, Geologia Ambiental e Economia, Laboratory of Atmospheric Chemistry [Paul Scherrer Institute] (LAC), Paul Scherrer Institute (PSI), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut des Sciences de la Terre [2011-2015] (ISTerre [2011-2015]), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble [1985-2015] (OSUG [1985-2015]), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology [2007-2019] (Grenoble INP [2007-2019])-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology [2007-2019] (Grenoble INP [2007-2019])-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géologie de l'ENS (LGENS), Institut des Sciences de la Terre de Paris (iSTeP), Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Volcanic arc, business.industry, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Triple junction, Kinematics, Slip (materials science), 010502 geochemistry & geophysics, Geodesy, 01 natural sciences, Plate tectonics, Geophysics, Sinistral and dextral, Global Positioning System, General Earth and Planetary Sciences, business, Geology, Seismology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract: [1] The Polochic-Motagua strike-slip fault system in Guatemala marks the on-land plate boundary between the North American (NA) and the Caribbean (CA) plates. GPS observations in 1999 and 2003 show that the far-field velocity across the system (NA-CA relative velocity) is ∼20 mm/yr. This is significantly higher than the NUVEL-1A velocity but is consistent with the GPS based CA-NA velocity proposed by DeMets et al. (2000). The observations are modeled by a fault centered on the Motagua fault, locked at a depth of 20 km, with a slip-rate decreasing from eastern to central Guatemala from 20 to 12 mm/yr towards the NA-CA-Cocos triple junction. This decrease is accommodated by ∼8 mm/yr of E-W extension in the westernmost part of CA south of the Motagua fault. About 10 mm/yr of dextral slip is observed across the Mid-American Volcanic Arc. The NA-CA-Cocos triple junction is thus a complex, ∼400 km-wide wedge-shaped area.
Published: 2006
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31. Modeling the M L 4.7 mainshock of the February-July 2001 earthquake sequence in Aegion, Greece

Author: Efthimios Sokos, Hélène Lyon-Caen, A. Serpetsidaki, Jaromír Janský, Panayotis Papadimitriou, Jiri Zahradnik, Department of Geophysics, Charles University [Prague] (CU), Patras Seismological Laboratory, University of Patras [Greece], Département de sismologie, Institut de Physique du Globe de Paris, National Technical University of Athens [Athens] (NTUA), and CRLNET
Subjects: Focal mechanism, Rift, 010504 meteorology & atmospheric sciences, ASPO method, focal mechanism, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, 010502 geochemistry & geophysics, 01 natural sciences, Seismic wave, Azimuth, Strong ground motion, Geophysics, Amplitude, waveforms, Geochemistry and Petrology, Seismic moment, Corinth Rift, Structural geology, polarities, Geology, Seismology, 0105 earth and related environmental sciences
Abstract: International audience; An earthquake sequence comprising almost 2000 events occurred in February–July 2001 on the southern coast of the Corinth Gulf.Several location methods were applied to 171 events recorded by the regional network PATNET. The unavailability of S-wave readings precluded from reliable depth determination. For the mainshock of April 8, ML= 4.7, the depth varied from 0 to 20 km. The amplitude spectra of complete waveforms at three local stations (KER,SER, DES; epicentral distances 17, 26 and 56 km) were inverted between 0.1 and 0.2 Hz for double-couple focal mechanism and also for the depth. The optimum solution (strike 220°, dip 40°, rake ‒160°, and depth of 8 km) was validated by forward waveform modeling.Additionally, the mainshock depth was further supported by the P- and S-wave arrival times from the local short-period network CRLNET (Corinth Rift Laboratory).The scalar seismic moment was 2.5e15 Nm,and the moment rate function was successfully simulated by a triangle of the 0.5 second duration. This is equivalent to a 1–1.5 km fault length, and a static stress drop 2–6 MPa. This value is important for future strong ground motion simulation of damaging earthquakes in Aegion region, whose subevents may be modeled according to the studied event. The T axis of the mainshock (azimuth 176° and plunge 67°), is consistent with the regional direction of extension ∼N10°. However, none of the nodal planes can be associated to an active structure seen at the surface. The relationship of this earthquake sequence with deeper faults (e.g. possible detachment at about 10 km) is also unclear.
Published: 2004
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32. A new seismic tomography of Aigion area (Gulf of Corinth, Greece) from the 1991 data set

Author: Jean Virieux, Vadim Monteiller, Tiziana Vanorio, Hélène Lyon-Caen, T. Monfret, Diana Latorre, Jean-Luc Got, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Laboratoire Central des Ponts et Chaussées (LCPC)-Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Nice Sophia Antipolis (... - 2019) (UNS), and Université Côte d'Azur (UCA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Computation, [SDE.MCG]Environmental Sciences/Global Changes, seismic tomography, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], Induced seismicity, Vp •Vs, 010502 geochemistry & geophysics, 01 natural sciences, EXTENSION TECTONIQUE, Vp·Vs, Geochemistry and Petrology, Gulf of Corinth, Vp/Vs, TOMOGRAPHIE, 0105 earth and related environmental sciences, FAILLE, Model selection, Crust, MODELISATION, Data set, Geophysics, CROUTE CONTINENTALE, Seismic tomography, RIFT, SISMOLOGIE, PROPRIETE PHYSIQUE, GEODYNAMIQUE, Tomography, low-angle detachment, Parametrization, Geology, Seismology
Abstract: International audience; A new three-dimensional delay traveltime tomography is performed to image the intermediate structure of the western Gulf of Corinth. A large data set, collected in 1991 during a two-month passive tomographic experiment, has been reanalysed for the reconstruction of detailed Vp and Vs images. An improved tomography method, based on an accurate traveltime computation, is applied to invert simultaneously delayed P and S first-arrival traveltimes for both velocity and hypocentre parameters. We perform different synthetic tests to analyse the sensitivity of tomography results to the model parametrization and to the starting 1-D model selection. The analysis of the retrieved Vp and Vs models as well as deduced Vp/Vs and Vp·Vs images allows us to interpret and delineate the distribution of lithological variation, porosity/crack content and fluid saturation in the upper 9–11 km of the crust beneath the gulf. The tomographic models image a rather complex crustal structure, which is characterized by a vertical change in both velocity features and seismicity distribution. We identify a shallower zone of the crust (0–5 km depth), in which velocity distributions seem to be controlled by the still active N–S extensional regime and a deeper zone (7–11 km depth), which matches the seismogenic zone. The correlation between this latter and a specific unit of the Hellenic mountain structure (the Pyllite–Quartzite series) allows us to suggest a possible explanation for seismicity concentration in a narrow band at 7–9 km depth. Finally, the occurrence of clusters showing low-angle normal fault mechanisms in areas characterized by high Vp/Vs values indicates a possible role of fluids in triggering brittle creep along the identified low-angle normal faults.
Published: 2004
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33. Converted seismic wave investigation in the gulf of Corinth from local earthquakes

Author: Diana Latorre, Jean Virieux, Hélène Lyon-Caen, T. Monfret, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
Subjects: METHODE D'ANALYSE, Global and Planetary Change, 010504 meteorology & atmospheric sciences, ANALYSE DES PHASES CONVERTIES, SISMOGRAMME, 010502 geochemistry & geophysics, 01 natural sciences, Seismic wave, ONDE SISMIQUE, General Earth and Planetary Sciences, Waveform, SISMOLOGIE, Seismogram, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: We propose a procedure for the detection of converted phases in seismograms between the P- and S-arrivals. This procedure has been successfully applied to waveforms of different stations from the 1991 passive experiment around the Aigion area (Greece). Three major converted phases have been detected at two stations on the northern Gulf of Corinth. The first phase has been interpreted as a P-to-S transmitted wave occurring at an interface located at a depth of 3 km in the northern part of the Psaromita Peninsula. The two later phases that have a more complex polarisation might come from deeper interfaces. To cite this article: D. Latorre et al., C. R. Geoscience 336 (2004).
Published: 2004
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34. First results of the CRLN seismic network in the western Corinth Rift: evidence for old-fault reactivation

Author: Hélène Lyon-Caen, K. Makropoulos, Panayotis Papadimitriou, Pascal Bernard, F. Pacchiani, G. Patau, Anne Deschamps, Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Global and Planetary Change, geography, geography.geographical_feature_category, Rift, 010504 meteorology & atmospheric sciences, Crust, Slip (materials science), Fault (geology), Induced seismicity, 010502 geochemistry & geophysics, 01 natural sciences, Stress field, General Earth and Planetary Sciences, Geology, Seismology, 0105 earth and related environmental sciences
Abstract: The 12 stations Corinth Rift Laboratory Seismological Network (CRLNET) aims at monitoring the seismicity (Ml>1) in the CRL area and at constraining the geometry of active structures at depth. Two years of microseismicity (2000–2001) recorded by the CRLNET in the Aigion area shows: (1) background seismicity inside the Corinth rift at depth of 4.5–11 km, deepening towards the north and no activity in the upper 4 km of the crust – this seismicity is not clearly related to major faults observed at the surface –; (2) a swarm, 6 km south of the city of Aigion, associated with the Mw=4.2, 8 April 2001 earthquake. This earthquake occurred at 6 km depth, on a SW–NE oriented fault dipping 40° to the northwest and corresponds to normal faulting with a right lateral component of slip. It likely occurred on an old structure reactivated in the present stress field. To cite this article: H. Lyon-Caen et al., C. R. Geoscience 336 (2004).
Published: 2004
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35. Active deformation of the Corinth rift, Greece: Results from repeated Global Positioning System surveys between 1990 and 1995

Author: Pierre Briole, Denis Hatzfeld, Jean-Claude Ruegg, K. Papazissi, Amalia Balodimou, C. Mitsakaki, Anne Deschamps, Alexis Rigo, Hélène Lyon-Caen, G. Veis, Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire de géologie de l'ENS (LGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), National Technical University of Athens [Athens] (NTUA), Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Laboratoire Central des Ponts et Chaussées (LCPC)-Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA), CRLNET, Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Laboratoire de géologie de l'ENS (LGENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, GPS, Soil Science, Magnitude (mathematics), [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Active fault, triangulation, Aquatic Science, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Corinth Rift, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Rift, Ecology, Greec, Seismotectonics, extension, deformation, Paleontology, Forestry, Crust, seismic deformation, Geodesy, Seismogenic layer, Tectonics, Geophysics, Space and Planetary Science, Rift zone, Seismology, Geology
Abstract: International audience; Between 1990 and 1995, we carried out seven Global Positioning System (GPS) campaigns in the Corinth rift area in order to constrain the spatial and temporal crustal deformation of this active zone. The network, 193 points over ∼10,000 km2, samples most of the active faults. In order to estimate the deformation over a longer period, 159 of those points are also Greek triangulation pillars previously measured between 1966 and 1972. Two earthquakes of magnitude 6.2 and 5.9 have occurred in the network since it was installed. The extension rate deduced from the analysis of the different GPS data sets is 14±2 mm/yr oriented N9° in the west, 13±3 mm/yr oriented S-N in the center, and 10±4 mm/yr oriented N19°W in the east of the gulf. The comparison between GPS and triangulation gives higher rates and less angular divergence (25±7 mm/yr, N4°E; 22±7 mm/yr, S-N; 20±7 mm/yr, N15°W, respectively). Both sets of data indicate that the deforming zone is very narrow (10–15 km) in the west, might be wider in the center (15–20 km), and is more diffuse in the east. The analysis of the displacements observed after the Ms = 6.2, June 15, 1995, and the Ms = S.9, November 18, 1992, earthquakes, both located in the west of the gulf, together with seismological and tectonic observations shows that these two earthquakes occurred on low-angle (≤35°) north dipping normal faults located between 4.5 and 10 km depth in the inner part of the rift. Assuming that the deformation is concentrated in relatively narrow deforming zones, we use a simple model of a dislocation in an elastic half-space to study the implication of the localization. Using the geometry of the known seismogenic faults, our observations imply continuous aseismic deformation in the uppermost crust of the inner rift. This model predicts geodetic strain rates close to seismic strain rates in opposition to previous estimates. This is because our model takes into account the activity on low-angle normal faults in the inner rift and an effective seismogenic layer of 6–7 km, about half that usually assumed.
Published: 2000
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36. Effects of superficial layers on coseismic displacements for a dip-slip fault and geophysical implications

Author: Pierre Briole, Rodolphe Cattin, Pascal Bernard, Hélène Lyon-Caen, Patrick Pinettes, Département de sismologie, and Institut de Physique du Globe de Paris
Subjects: elastic dislocation, 010504 meteorology & atmospheric sciences, Magnetic dip, Modulus, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Slip (materials science), 010502 geochemistry & geophysics, 01 natural sciences, Physics::Geophysics, Planar, normal-faulting earthquakes, Geochemistry and Petrology, Gulf of Corinth, Corinth Rift, 0105 earth and related environmental sciences, coseismic displacements, Greece, Geodetic datum, Geophysics, Geodesy, Finite element method, crustal structure, Displacement field, Seismic moment, Geology
Abstract: International audience; We study the effect of a superficial layer overlying a half-space on the surface displacements created by a dip-slip dislocation on a planar rectangular fault using a 2-D finite element model. The effect of the density and Poisson’s ratio is negligible. On the other hand, the contrast in Young’s modulus between the top layer and the half-space below significantly affects the modelled coseismic displacements. The horizontal displacements are more sensitive than the vertical displacements to the existence of the top layer. Near the fault, a low-rigidity layer with a Young’s modulus of 10 GPa can increase the horizontal displacements by up to 40 per cent. An analytical 3-D half-space model is used to interpret this effect in terms of an ‘equivalent’ homogeneous model. The presence of a top layer can be partly simulated in a homogeneous half-space by perturbing the depth and the slip on the fault from their ‘real’ values to ‘equivalent’ values. For a given displacement field observed at the surface, the perturbations in fault depth and slip can reach 1km and 25 per cent respectively. The fault dip angle is not model-dependent. We conclude that for the accurate estimation of fault depth and slip from coseismic geodetic data, rigidity contrasts existing within the upper crust must be taken into account. Not taking into account the effect of an existing low-rigidity layer also leads to an underestimation of seismic moment release. This may in part be the cause of apparent discrepancies between seismic and geodetic moment releases in particular areas such as the Gulf of Corinth, Greece.
Published: 1999
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37. Earthquake mechanisms of the Adriatic Sea and Western Greece: implications for the oceanic subduction-continental collision transition

Author: Hélène Lyon-Caen, Donald L. Hatzfeld, Calum Baker, Elephteria Papadimitriou, Alexis Rigo, Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris, Geophysical Laboratory [Thessaloniki], Aristotle University of Thessaloniki, Laboratoire de Géophysique Interne et Tectonophysique, Institut de Recherche Interdisciplinaire de Géologie et de Mécanique (IRIGM), Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Hellenic arc, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, Adriatic Sea, 010504 meteorology & atmospheric sciences, Continental collision, Subduction, Slip (materials science), Fault (geology), 010502 geochemistry & geophysics, Collision zone, 01 natural sciences, Geophysics, continental collision, Geochemistry and Petrology, oceanic subduction Western Greece, Convergent boundary, Eclogitization, earthquake mechanisms, Seismology, Geology, 0105 earth and related environmental sciences
Abstract: International audience; We present 21 focal solutions (magnitude > 5.5) reliably computed by body-wave modelling for the western Hellenic arc from Yugoslavia to the southern Peloponnese. Mechanisms located within the Aegean show normal faulting, the Taxis trending N-S in the centre and parallel to the active boundary in the external part. Mechanisms associated with the Keffalinia fault are consistent with dextral strike-slip motion. Reverse mechanisms located along the active boundary are remarkably consistent and do not depend on the nature of the active boundary (continental collision or oceanic subduction). The consistency in azimuth of the slip vectors and of the GPS velocity relative to Africa, all along the active boundary, suggests that the deformation is related to the same motion. The discrepancy between seismic-energy release and the amount of shortening confirms that the continental collision is achieved by seismic slip on faults but the oceanic subduction is partially aseismic. The northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent evolution of the active subduction.
Published: 1997
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38. The 1986 Kalamata (South Peloponnesus) Earthquake: Detailed Study of a Normal Fault, Evidences for East-West Extension in the Hellenic Arc

Author: J. Drakopoulos, Rolando Armijo, J. Baskoutass, G. Pedotti, V. Kouskouna, D. Papanastassiou, R. Gaulon, Hélène Lyon-Caen, Panayotis Papadimitriou, J. Latoussakis, N. Delibassis, Konstantinos Makropoulos, Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Department of Geophysics & Geothermics - NKUA, NKUA, National Observatory of Athens (NOA), Department of Geophysics and Geothermics, National Observatory of Athens, and ISARS
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Soil Science, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Aquatic Science, Fault (geology), 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Echelon formation, Earthquake rupture, Aftershock, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Hellenic arc, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, Focal mechanism, geography, geography.geographical_feature_category, Ecology, Subduction, Paleontology, Forestry, Tectonics, Geophysics, Space and Planetary Science, Seismology, Geology
Abstract: International audience; Tectonic and seismological data collected in the field following the September 13, 1986, Kalamata earthquake (south Peloponnesus) are presented and analyzed to discuss the earthquake rupture process and the regional tectonics. The event occurred on the Kalamata normal fault whose trace was mapped with SPOT images and topographic and field observations. This fault is part of an approximately NNW-SSE en •chelon system cutting through the Hellenic nappes. The fault striking N15°E on the average, with a dip of about 50°, has a minimum cumulated Quaternary throw of the order of 1 km. The measured coseismic slip is 6-18 cm over a length of 6 km. The main shock focal mechanism obtained from long-period waveform modeling (strike=201° (+ 10 °, -20°), dip=45°+/- 5°, rake= 283° (+ 10°, -25°)) represents almost pure east-west extension and is in good agreement with tectonic observations. The centroid depth is constrained to 5+/-3 km and the seismic moment to 7.0 +/- 2.5 x 10+17 N m. Over 700 aftershocks, located by a 16-station network installed after the earthquake for a period of 2 weeks, define two clusters separated by a "gap" of aftershock activity, from the surface to a depth of about 10 km. The main cluster, to the south, defines a 45° west dipping plane which lies on the downward extension of the fault mapped at the surface. Focal mechanisms of aftershocks on this fault plane are homogeneous and represent E-W extension as the main shock. In contrast, the majority of focal mechanisms in the uppermost part of the footwall show more or less E-W compression, probably corresponding to postseismic stress release. The northern cluster of aftershocks is very dense and located away from the surface rupture, within a relay zone between the Kalemate and the next en échelon faults to the NW, the Thouria faults. There focal mechanisms represent extension from about N115° to N70° and N20°, corresponding mostly to fault reactivation in an area where nonrigid deformations prevail. The main shock probably initiated in this relay zone 3-4 s before the rupture front reached the main fault plane and released most of the energy there, the rupture presumably propagating southward. The focal mechanism of the Kalamata earthquake and that of the April 27, 1965, earthquake located to the northwest of Crete, as well as the regional active normal fault pattern, imply that E-W extension oblique to the Hellenic arc is presently the dominant tectonic regime. E-W stretching occurs partly on reactivated NW-SE faults parallel to the Hellenic structures but mostly on newly formed N-S normal faults across those structures. The latter faults are responsible for the apparent segmentation of the Hellenic belt from southern Peloponnesus to Crete. The existence of active E-W extension in this region implies a recent change in the tectonic regime and consequently a change in boundary conditions at the subduction zone, probably in response to the incoming margin of Africa.
Published: 1988

39. Double-difference relocation of earthquakes in central-western Mongolia, 1964-2017.

Author: Davaasuren, Ganzorig, Yann, Klinger, Pascal, Bernard, Hélène, Lyon-Caen, Sodnomsambuu, Demberel, and Munkhuu, Ulziibat
Published: 2019

40. Seismic Hazard and Earthquake Rate In Fault Systems - SHERIFS : a python tool for earthquake geologists, fault-hazard modelers and decision-makers.

Author: Chartier, Thomas, Oona, Scotti, and Hélène, Lyon-Caen
Published: 2018

41. Characterizing ground motion of historical earthquakes. Study of Sant’Agata del Mugello combining building archaeology, earthquake engineering andseismology

Author: MONTABERT, Arnaud, Laboratoire de mécanique et technologie (LMT), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Ecole Normale Supérieure Paris-Saclay (ENS Paris Saclay), Ecole Normale Supérieure (ENS), Paris, FRA., Hélène Lyon-Caen(Helene.Lyon-Caen@ens.fr), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Archéologie et Philologie d'Orient et d'Occident (AOROC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL), Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-aux-Roses, and Ecole Normale Supérieure, Institut de Radioprotection et de Sûreté Nucléaire
Subjects: [PHYS.MECA.VIBR]Physics [physics]/Mechanics [physics]/Vibrations [physics.class-ph], mouvement sismique historique, archéologie de la construction, modèle d’endommagement continu, analyse dynamique linéaire, [SHS.ARCHEO]Humanities and Social Sciences/Archaeology and Prehistory, continuum damage model, historical ground motion, vibration-based model updating, analyse modale opérationnelle, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], Sant’Agata del Mugello, méthode des éléments finis calibration de modèle, operational modal analysis, [PHYS.MECA.STRU]Physics [physics]/Mechanics [physics]/Structural mechanics [physics.class-ph], Apennins, building archaeology, linear dynamic analysis, Finite element model
Abstract: A fault is charged during (hundred-) thousand years, then the accumulated elastic energy is released in few secondswhen an earthquake occurs. To correctly assess seismic hazard it is of capital importance to study the seismic history.Over the last decades approaches such as historical seismology, archaeoseismology and paleoseismology have beendevelopped chasing alternative sources of information. Among them, historical buildings witnessed ancient earthquakesas “stone seismometers” recorded in their walls as structural disorders and repairs. I develop an innovative methodologyconnecting building archaeology, seismology and earthquake engineering. I aim to show that archaeological characteri-zation of post-seismic repairs on historical buildings can successfully infer key ground motion characteristics of historicalearthquakes. The test case is the medieval church of Sant’Agata del Mugello, an exceptional site with many historicalsources describing the damages induced by past earthquakes, and their renovation. The site is located in the Mugellobasin (Central Apennines, Italy, Tuscany), characterized by a moderate seismicity. The largest known events occurredin 1542 (Mw 6) and 1919 (Mw 6.3). I first trace the seismic history of the church by combing a stratigraphic analysisof the buidling with an in-depth study of historical texts. A CAD-based model of the current church is designed from alaser scanner survey. A CAD-model of the church before and after each historical earthquake is then extrapolated fromthe current church and its deduced constructive history. I have developed an ad hoc meshing code to generate a finiteelement mesh from the CAD-based model. We perform two ambient vibration testing survey in the church. 8 modes ofvibration (natural frequency, modal shapes and damping ratio) are estimated. A Vibration-Based model updating basedon the identified experimental parameters and the constructive history of the church allows to calibrate the numericalmodel of the church in its linear part. A continuum damage model is used to identify the limit of the linear model of thechurch. I then focus on the study of the 1919 non damaging earthquake. A collection of waveforms compatible with theseismotectonic context is selected, corrected, and used to solicit the updated linear digital model of the church. I showpreliminary results to discuss the ground motion characteristics of the 1919 earthquake.; La déformation accumulée pendant plusieurs centaines (milliers) d’années dans les zones de failles est brusquementrelâchée en seulement quelques secondes lorsqu’un séisme se produit. L’étude des séismes anciens à travers dif-férentes échelles de temps est d’une importance capitale pour améliorer l’évaluation de l’aléa sismique. Au cours desdernières décennies des approches, telles que la sismologie historique, l’archéosismologie et la paléosismologie ontété développées pour chercher diverses sources d’informations. Parmi elles, les bâtiments historiques, tels des "sis-momètres de pierre" peuvent être utilisés pour témoigner de cette sismicité passée qu’ils ont enregistrée dans leursmurs sous forme de dégâts ou de réparations. Je propose une méthodologie innovante reliant l’archéologie de la con-struction, la sismologie et le génie sismique afin de démontrer que la caractérisation archéologique des réparationspost-sismiques sur les bâtiments historiques peut permettre de déduire les principales caractéristiques du mouvementsismique. Cette méthodologie est développée autour du cas de l’église médiévale de Sant’Agata del Mugello, un siteexceptionnel dont les dommages et les réparations induits par les séismes sont décrits par de nombreuses sourceshistoriques. Le site est situé dans le bassin du Mugello (Apennin central, Italie, Toscane), caractérisé par une sismicitémodérée. Les plus grands événements connus se sont produits en 1542 (Mw∼6) et 1919 (Mw∼6.3). Nous commençonspar retracer l’histoire sismique de l’église en combinant une analyse stratigraphique du bâtiment avec une étude appro-fondie des textes historiques. Un modèle de CAO est conçu à partir d’un relevé géométrique issu d’une campagne descanner laser. Un modèle de CAO de l’église avant et après chaque séisme historique est ensuite extrapolé à partir dumodèle de l’église actuelle et de son histoire constructive. Un code de maillage ad hoc a été développé pour générerun maillage aux éléments finis à partir du modèle de CAO. Deux campagnes de vibrations ambiantes ont été menéesdans l’église de Sant’Agata. 8 modes de vibration (fréquence propre, déformée modale et amortissement) sont estimés.Un processus d’optimisation des paramètres modaux, permet de calibrer le modèle numérique de l’église dans sa partielinéaire. Un modèle d’endommagement continu est utilisé pour identifier la limite du modèle linéaire de l’église. Je meconcentre ensuite sur l’étude du séisme historique de 1919 qui n’a pas causé de dommages. Une collection de mouve-ments sismiques compatibles avec le contexte sismotectonique est sélectionnée, corrigée et est utilisée pour solliciter lemodèle numérique linéaire calibré de l’église. Je présente des résultats préliminaires pour discuter des caractéristiquesdu mouvement sismique associé au séisme historique de 1919.
Published: 2021

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