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SUMMARYOuter Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, considered a foreshock, and culminated with the main shock on 26 November 2019, followed by a paramount aftershock activity. We propose a model for the coseismic slip distribution using InSAR, permanent, and campaign GNSS measurements. We tested two hypotheses: an earthquake on a thrust plane with the direction N160° and along with a back thrust. By varying the depth and dip angle for the first hypothesis and only the dip angle for the second hypothesis, we concluded the optimal solution is a blind thrust at a 15-km depth dipping eastward 40°, a maximum slip of 1.4 m and an Mw 6.38. A GNSS time-series obtained after 2020 shows two slow slip events (SSEs): the first one is 200 d after the main shock up to 26 d, and the second one is 300 d after the main shock up to 28 d. We tested three hypotheses: SSE along the basement thrust where the main shock has been localized, SSE along the flat formed by the detachment layer of the cover, and SSE along these two faults. We concluded that SSE occurred along the detachment layer or along the two faults.

SUMMARY On 2013 September 24, an earthquake of magnitude Mw 7.7 occurred on the Hoshab Fault in southern Pakistan, south of the 650-km-long Chaman Fault, within the eastern Makran accretionary wedge. This earthquake was caused predominantly by strike-slip faulting. To quantify the post-seismic deformation following this large earthquake, we used ascending and descending Sentinel-1 data over the period 2014 November–2017 December. The deformation time-series over these 3 years shows that the post-seismic deformation was not linear over the time. To determine the mechanisms that may have driven post-seismic deformation, such as after-slip or a combination of after-slip and viscous relaxation, we explored some models, including after-slip only, and a combination of after-slip and viscous relaxation, to identify the best fit between the observed and simulated deformation time-series. Our results indicate that after-slip was the main mechanism controlling the post-seismic deformation. The introduction of a basal flat fault in the modelling improves the fit between the model results and the time-series obtained from the satellite images This basal fault is located at a depth of 18 km, has a northward dip of 7° and corresponds to the basal décollement level of the Makran accretionary prism.

Resumen Desde inicios del año 2015 y en el marco del proyecto Red de Observación de Operación Continua GPS del Caribe (COCONet) se han instalado seis estaciones de observación continua del Sistema de Posicionamiento Global (cGPS) y meteorología en el territorio venezolano (El Baúl-CN41, Quebrada Arriba-CN39, Isla de AvesCN49, Los Roques-CN42, Isla de Margarita-CN44 e Isla La Blanquilla-CN43). Adicionalmente, se instalaron otras dos estaciones geodésicas: Saucedo-SAU0 y La Pica Arriba de Catuaro-PAC0, así como un extensómetro a través de la falla El Pilar como parte del proyecto VENCREEP (ANR-Francia). En tal sentido, en el marco del proyecto Tsunami FONACIT 2013000361 ya han sido adquiridas siete estaciones permanentes de nueva generación de las 15 previstas, las cuales serán estratégicamente ubicadas para densificar la red existente en el corto plazo. Estas estaciones permitirán comprender mejor la geodinámica local y regional con implicaciones importantes en el estudio de la amenaza sísmica. Abstract Since 2015 six new continuous Global Positioning System (cGPS) and meteorological stations have been installed in Venezuela as part of the Continuously Operating Caribbean GPS Observational Network (COCONet) project (El Baúl-CN41, Quebrada Arriba-CN39, Isla de Aves-CN49, Los Roques-CN42, Isla de Margarita-CN44, and Isla La Blanquilla-CN43). Almost simultaneously, in the framework of the VENCREEP project (ANR-France), a survey composed of two geodetic stations (Saucedo-SAU0 and La Pica Arriba de Catuaro-PAC0) and one creepmeter was installed to study the Pilar Fault. Also, new seven cGPS stations of fifteen planned were acquired through the Tsunami project (FONACIT 2013000361), aiming at densifying the current network. The whole set of stations will improve our knowledge about the local and regional geodynamics. We are sure that the results will have implications for seismic hazard studies.

The pattern of active deformation of Himalayan frontal structures is complex with out-of-sequence reactivations in the chain and development of scarps associated to earthquake ruptures reaching the surface in the piedmont. We analyze passive seismic records using the Horizontal-to-Vertical Spectral Ratio method along three North-South trending profiles of the Darjeeling Himalayan piedmont, revealing subsurface structures down to 600 meters and imaging the Siwalik sedimentary rocks / recent deposits interface. We find evidence for a thrust fold system hidden beneath the plain correlated to geomorphologic scarps revealed by topographic profiles. These morphological surfaces are incised by large rivers of the piedmont by several tens of meters during phases of low sedimentation, thus slightly emerging in the plain. These scarps are supposedly induced by thrust deformation related to great earthquakes propagating south of the morphological front and inducing subsurface ruptures in the piedmont. This interpretation is comforted by the lateral correlation of the imaged thrusts and associated folds with previously evidenced fault scarps associated to active thrusts of the Darjeeling piedmont. In the piedmont of East/Central Nepal, oil company seismic profiles image similar thrusts and associated folds that can also be correlated to both local incision of small rivers draining the southern flank of the Siwalik hills, and uplift evidenced by a previously analyzed leveling profile.The long-term kinematic evolution of this hidden thrust fold belt is slow, with a tectonic uplift of the hangingwall lower than the subsidence rate of the foreland basin, i.e., less than ~ half a millimeter per year. The evolution of the hidden structures corresponds to that of an embryonic thrust belt affected by a layer parallel shortening (LPS) acting in the long term with a shortening rate of the order of 5-10% of the shortening rate of the whole Himalayan thrust system. An aseismic deformation associated with the LPS structures that could absorb the entire deformation of the embryonic thrust belt in East/Central Nepal is suggested by the comparison of the long term structural evolution with geodetic and paleoseismological studies. The amplitude of this aseismic deformation is however too limited to significantly reduce the seismic hazard in the Himalayan piedmont.

International audience; The morphological boundary between the Himalayas and the foreland plain is well expressed and most often corresponds to the frontal emergence of the Main Himalayan Thrust (MHT). This boundary is affected by surface ruptures during very large Himalayan earthquakes (Mw > 8) that regularly induce (with a recurrence of the order of 500 to 1,200 years) the uplift of the foothills relative to the plain. However, a thrust-fold system is hidden beneath the plain and is displayed by the seismic profiles of oil companies in east/central Nepal and by H/V passive geophysical techniques in Darjeeling. Its long-term kinematic evolution is slow, with a tectonic uplift of the hanging wall that is lower than the subsidence rate of the foreland basin, that is, less than approximately half a millimetre per year. During phases of low sedimentation controlled by climatic fluctuations, the morphological surfaces of the piedmont are incised by large rivers for several tens of metres; therefore, structures hidden under the sediments emerge slightly in the plain. The evolution of the hidden structures corresponds to an embryonic thrust belt mainly affected by a long-term shortening rate of 1.4 +2.5 /-1.2 mm•yr-1 , that is, 2-20% of the shortening rate of the entire Himalayan thrust system. Nonetheless, the details of the deformation associated with the embryonic thrust belt are still poorly understood. Several deformation components could affect the central Himalayan and Darjeeling piedmonts. i) Any slow steady-state deformation, such as layer parallel Earth Science Review 2 shortening (LPS) is not detected by Global Navigation Satellite System (GNSS) data, and such deformation would therefore absorb less than 0.5 mm•yr-1. The geodetic data that suggest the aseismic growth of some of the structures are highly controversial. ii) For the rest of the deformation of the embryonic thrust wedge, it is yet to be proven whether deformation occurs during rare great earthquakes affecting the piedmont during medium earthquakes and/or during post-seismic deformation related to great earthquakes. The amplitude of this long-term low deformation is too limited to significantly reduce the seismic hazard in the seismic gaps of the Himalayan belt. iii) In some portions of the Himalayan front, such as Darjeeling (India), the thrust deformation related to great earthquakes propagates several tens of kilometres south of the morphological front in the zone previously affected by the long-term low deformation. It induces multi-metre surface ruptures in the piedmont and a mean shortening of 8.5 ± 6.2 mm•yr-1. iiii) Pre-existing faults in the bedrock of the Indian craton, often oblique to the Himalayan structures, are locally reactivated beneath the foreland plain with low deformation rates.

International audience; We study translation, rotation, and strain of active tectonic blocks in Northeastern Venezuela from the Global Navigation Satellite System (GNSS) observations. Since the installation of the geodetic network in 2003, one of the goals was to place at least three observation sites at each tectonic block to study the deformation of each one. Based on this premise, we define at least seven blocks: Bergantín and Caripe blocks south of the El Pilar Fault (EPF), and Cariaco Gulf, Land bridge, Paria, North Peninsula, and Margarita Island blocks north of the EPF. Our preferred block modeling shows angular rotations from 0.02 to 0.29° Ma−1. It is known that the EPF concentrates the active deformation in this region of the Caribbean-South American plate boundary. However, the existent rotation could accommodate part of the motion. The strain rate tensors (SRT) indicate NW-SE compression and NE-SW extension for the western blocks. To the east, the 4-Land bridge block keeps the NW-SE compression but shows a decrease in the extensional component. The 5-Paria blocks show a complete inversion in the sense of semi-axis. Additionally, we evaluate the possibility of different motions in Margarita block calculating translational vector, rotational velocity, and strain from three GNSS sites at each side thereof. Our results show remarkable similarities for the Macanao Peninsula and Eastern Margarita Island, pointing to both belonging to a single block.

Data of the paper "Seismic coupling quantified on inferred décollements beneath the western syntaxis of the Himalaya" published by Tectonics; International audience; We used episodic GNSS measurements to quantify the present-day velocity field in the northwestern Himalaya from the Himalayan foreland to the Karakoram Range. We report a progressive N-S compressional velocity gradient with two noticeable exceptions: in the Salt Range, where important southward velocities are recorded, and in Nanga Parbat, where an asymmetrical E-W velocity gradient is recorded. A review of Quaternary slip along active thrusts both in and out of sequence allows us to propose a 14 mm/year shortening rate. This constraint, together with a geometrical model of the MHT, allows us to propose estimations of the slip distributions along the active faults. The lower flat of the MHT is characterized by ductile slip, whereas the coupling increases along the crustal ramp and along the upper flat of the MHT. The basal thrust of the Potwar Plateau and Salt Range presents weak coupling, which is interpreted as the existence of a massive salt layer forming an excellent décollement. In the central part of the frontal Salt Range, the velocities suggest the existence of a southward horizontal flux in the massive salt layer. The simulations also suggest that the velocities recorded in Nanga Parbat can be explained by active westward thrusting along the fault that borders the massif to the west. Simulations suggest that the slip along this fault evolves with depth from 5 mm/year ductile slip near the MHT to no slip along the upper part of the fault.

11 pages; International audience; In Kashmir Himalaya, the Medlicott-Wadia Thrust is a main active fault responsible for the crustal accretionary prism building during the Late Quaternary. Because of the long seismic silence during the last five centuries, it is a key structure to be studied in order to estimate the regional seismic hazard. In the Riasi area, the analysis of two paleoseismological trenches allowed us identifying and measuring several seismic ruptures over the last ~3500 years. We determined that the oldest rupture occurred around 1600–1000 BC, while the youngest occurred after 1470 AD. The latest event is compatible with the great 1555 AD (Mw > 7.5) Kashmir earthquake, whose evidence at the surface had not yet been recognized. Our results show that despite the long-lasting seismic gap, the Medlicott-Wadia Thrust is a main seismogenic structure in the region, able to produce large earthquakes. Their recurrence interval ranges between 500 and 700 years, implying that a main seismic event could occur in the next decades. These seismic ruptures are localized over gently-dipping fault branches associated with decameter-scale scarps. The morphologies observed are due to a significant non-localized component of the deformation in Quaternary sediments.

The western limb of the Hellenic Arc defines the boundary of a large intracontinental active extensional domain covering the Aegean and the southwestern part of the Balkan peninsula. Along this boundary a transition from collision in the north to subduction in the south is associated with post-Miocene clockwise rotations of ∼ 50 ∘ . We present a new GPS velocity field that, with new permanent station velocities in Albania, Bulgaria, Kosovo, Montenegro, and Northern Macedonia, provides insights into previously unresolved aspects on the large-scale dynamics of continental lithosphere and on the relation between long and short-term kinematics. In particular we address (1) the kinematic description of the collision/subduction transition, (2) the relation between long-term finite rotations with geodetically-measured instantaneous rotations, (3) the forces maintaining and resisting the deformation of the extensional domain and (4) the extent of its northern boundary. We use the analogy of rigid elongate inclusions in the velocity field to predict the senses and approximate rates of rotation of crustal blocks in the deforming continental region. Across the collision/subduction transition zone a large rotational pattern in the velocity field is found whose spatial pattern and sense of rotation is compatible with the observed paleomagnetic rotations through the occurrence of fault-bounded block rotations. Geodetic observations show that clockwise vertical axis rotation of the western limb of the Hellenic margin is active today, with distribution and rates that are essentially the same as that defined by the paleomagnetic data for the last 5 Ma. The maximum rates of the rotational component of the velocity field is found along the wide arrangement of fault-bounded blocks in central Greece that accomodate the NE-SW dextral shear transferred from the northern Aegan trough. The northern limit of the rotating margin defines a hinge (Scutari-Pec transverse zone) that has remained stationary throughout the Middle Miocene (relative to the upper plate of the collision/subduction system) with important implications for the distribution of strength of the western margin of the Hellenic Arc. The distribution and style of deformation along the western boundary of the extensional domain is controlled by the relation between gravitational forces, driving the flow of crustal material towards the low-lying adjacent regions sea floor, and heterogeneous resistive forces along the collision/subduction boundary.

We present the results of a structural neotectonic survey undertaken on the Mahesian Anticline in the frontal Himalaya of Pakistan. This anticline resulted from the folding of Precambrian to Tertiary layers that was controlled by a thrust and a backthrust, interacting in a complex way. Four generations of fluvial terraces formed by the Jhelum River and two tributaries have been distinguished on the SE flank of the anticline. Two of these terraces, T2 and T3, have been left hanging by fold development and have been dated by cosmogenic 10 Be to 6.5 ± 0.2 ka and 3.3 ± 0.7 ka, respectively. From such ages an uplift rate of ∼10 mm/y was determined for the Holocene. That uplift is induced by a shortening rate of ∼10 mm/y. We highlight that the Mahesian Anticline and Frontal Salt Range Thrust, together with the Kalabagh western lateral ramp and the Jhelum eastern lateral ramp, delineate the active tectonic boundary of the Potwar Plateau. This thrust sheet moves above the salt level without out-of-sequence deformation. Moreover, the small but significant difference between the long-term deformation rates (8.4 mm/y) and the geodetic velocities (2–5 mm/y) detected for the Central Potwar Plateau seems to be linked to episodic spurts of accelerated creeping of the thick salt level, triggered by earthquakes located to the north on the deep (>15 km) part of the MHT. In addition, the large difference between the long-term deformation rates and the geodetic velocities (less than 2 mm/y) reported for the eastern Potwar Plateau seems to be linked to the accumulation of a slip deficit around asperities formed where the salt is missing. This deficit may be recovered during earthquakes potentially as great as Mw 7.

International audience; We put the 25 April 2015 earthquake of Nepal (Mw 7.9) into its structural geological context in order to specify the role of the segmentation of the Himalayan megathrust. The rupture is mainly located NW of Kathmandu, at a depth of 13-15 km on a flat portion of the Main Himalayan Thrust (MHT) that dips towards the N-NE by 7-10°. The northern bound of the main rupture corresponds to the transition towards a steeper crustal ramp. This ramp, which is partly coupled during the interseismic period, is only locally affected by the earthquake. The southern bound of the rupture was near the leading edge of the Lesser Himalaya antiformal duplex and near the frontal footwall ramp of the upper Nawakot duplex. The rupture has been affected by transversal structures: on the western side, the Judi lineament separates the main rupture zone from the nucleation area; on the eastern side, the Gaurishankar lineament separates the 25 April 2015 rupture from the 12 May 2015 (Mw 7.2) rupture. The origin of these lineaments is very complex: they are probably linked to pre-Himalayan faults that extend into the Indian shield beneath the MHT. These inherited faults induce transverse warping of the upper lithosphere beneath the MHT, control the location of lateral ramps of the thrust system and concentrate the hanging wall deformation at the lateral edge of the ruptures. The MHT is therefore segmented by stable barriers that define at least five patches in Central Nepal. These barriers influence the extent of the earthquake ruptures. For the last two centuries: the 1833 (Mw 7.6) earthquake was rather similar in extent to the 2015 event but its rupture propagated south-westwards from an epicentre located NE of Kathmandu; the patch south of Kathmandu was probably affected by at least three earthquakes of Mw P 7 that followed the 1833 event a few days later or 33 years (1866 event, Mw 7.2) later; the 1934 earthquake (Mw 8.4) had an epicentre $170 km east of Kathmandu, may have propagated as far as Kathmandu and jumped the Gaurishankar lineament. This combined structural approach and earthquake study allows us to propose that the MHT in the central/eastern Himalaya is segmented by stable barriers that define barrier-type earthquake families. However for each individual earthquake within a family, the rupture histories could be different. Furthermore, the greatest earthquakes could have broken the barriers and affected the patches of several families. The concept of a regular recurrence of characteristic earthquakes is therefore misleading to describe the succession of Himalayan earthquakes.

Continuous monitoring of seismicity and surface displacement of active volcanoes can reveal important features of the eruptive cycle. Here high-quality GPS and earthquake data recorded at Grimsvotn volcano by the Icelandic Meteorological Office during the 2004-2011 intereruptive period are analyzed. These showed a characteristic pattern, with an initial similar to 2 year long exponential decay followed by similar to 3 year long constant surface displacement inflation rate. We model it by using a one magma reservoir model in an elastic damaging edifice, with incompressible magma and constant pressure at the base of the magma conduit. Seismicity rate and damage were first modeled, and simple analytical expressions were derived for the magma reservoir overpressure and surface displacement as functions of time. Very good fits of the seismicity and surface displacement data were obtained by fitting only three phenomenological parameters. Characteristic time and power strain show maxima from which reference times were inferred that split the intereruptive period into five periods. After the pressurization periods, damage occurring in the third period induced weakly nonlinear variations in magma overpressure and flow, and surface displacement. During the fourth period, the damage dominated and variations became more strongly nonlinear, the reservoir overpressure decreased, and magma flow increased. This process lasted until the power strain reached its second maximum, where instability was generalized. This maximum is a physical limit, the occurrence of which shortly precedes rupture and, eventually, eruption. This analysis allows characterization of the state of the volcanic edifice during the intereruptive period and supports medium-term prediction of rupture and eruption.

We analyze episodic (1995–2010) and permanent GNSS data quantifying interseismic velocities in the Himalaya of Nepal so as to constrain spatial variations in coupling along the Main Himalayan Thrust. To estimate this coupling, we model the MHT with the help of cross sections allowing us to constrain its changes in geometry from far-western Nepal to central and eastern Nepal. We determine that the upper flat of the MHT is nearly totally locked, the crustal ramp is partially locked, and that free slip is localized only along the lower flat north of the Himalaya. This location of increased coupling probably corresponds to the brittle/ductile change in rheology along the MHT and explains the location of very large (greater than the Gorkha 2015 event) earthquake epicenters north of the crustal ramp. Including the simulation of the Western Nepal Fault System in the continuation of the Karakorum fault does not improve simulation of the interseismic velocity field. The 25 April Gorkha earthquake nucleated in a highly coupled part of the upper flat of the MHT and propagated eastward along a less coupled part of the MHT.

In eastern Venezuela, the Caribbean - South American plate boundary follows the El Pilar fault system. Previous studies based on three GPS campaigns (2003 – 2005 – 2013) demonstrated that the El Pilar fault accommodates the whole relative displacement between the two tectonic plates (20 mm/yr) and proposed that 50 – 60 % of the slip is aseismic [Jouanne et al., 2011; Reinoza et al., 2015]. In order to quantify the possible variations of the aseismic creep in time and space, we conducted an InSAR time-series analysis, using the NSBAS method, on 18 images from the ALOS-1 satellite spanning the 2007 – 2011 period. During this 3.5 year period, InSAR observations show that aseismic slip decreases eastwards along the fault: the creep rate of the western segment reaches 25.3 ± 9.4 mm/yr on average, compared to 13.4 ± 6.9 mm/yr on average for the eastern segment. This is interpreted, through slip distribution models, as being related to coupled and un-coupled areas between the surface and ca. 20 km in depth. InSAR observations also show significant temporal creep rate variations (accelerations) during the considered time span along the western segment. The transient behavior of the creep is not consistent with typical postseismic afterslip following the 1997 Ms 6.8 earthquake. The creep is thus interpreted as persistent aseismic slip during an interseismic period, which have a pulse or transient like behavior.

The Holocene tectonic activity of Latin American countries is poorly constrained because of the short time span of the instrumental record and the lack of any seismic calendar during pre-colonization times. Therefore, some areas with low and diffused seismicity have been catalogued as a “seismic gap”. It has been suggested that the northernmost segment of the Bocono Fault in Venezuela is one of these areas, although a recent MW 7.4 event that occurred in 1812 has been well documented by a historical investigation. In this study, we mapped the historical events triggered by the Bocono Fault using a paleoseismological investigation, a geological interpretation of high-resolution satellite images, field mapping as well as ground-penetrating radar (GPR) profiles at selected trench sites. Our results suggest that at least three seismic events had produced surface ruptures in the trench site based on the exposed trench stratigraphy as well as the results of radiocarbon dating and age models: i) a latest event (E3) that occurred between 1545 and 1825 CE, ii) a previous event (E2) that occurred between 1483 and 1743 CE and iii) an older event (E1 before 1456–1636 CE). The E3 event might correspond to the 1812 major earthquake. These results further support the fact that the 1812 event was triggered by the Bocono Fault and that the rupture reached the surface. The potential slip deficit along the studied segment ranges from 1.7 to 2.3 m and corresponds to Mw ~7, assuming that the 1812 CE earthquake released all of the strain stored earlier. As the time span between events E2 and E3 is short (

The Kangra Reentrant is a convex-to-the-northeast U-shaped structure in the NW Himalaya, where the Sub-Himalayan fold-and-thrust belt is ∼90 km wide. This region has not been struck by large earthquakes since the 1905 Mw 7.8 Kangra Earthquake. Out-of-sequence deformation has been reported at the millennial timescale along intracrustal thrusts within this reentrant, such as the Jawalamukhi Thrust. Up to now, the occurrence of out-of-sequence deformation along inner thrusts within the Kangra Reentrant, during the Late Quaternary, has not yet been addressed. In this study, the results of a neotectonic survey undertaken in this reentrant are presented; the studied zone is located between the Beas and the Neogad rivers, and encompasses from the Jawalamukhi Thrust to the Main Boundary Thrust. Two terraces that are deformed by branches of the Medlicott-Wadia Thrust, locally named the Palampur Thrust, are identified; this is evidenced in the field by metric-scale fault scarps. By using 10Be dating, the ages of these terraces were constrained to ca. 7.5 and ca. 6.2 ka. This is clear evidence of the Late Quaternary out-of-sequence deformation in the innermost part of this reentrant, implying that strain is distributed along all the arc-orthogonal extent of the local fold and thrust belt over this timespan. A cumulative slip rate of ca. 1 mm/yr along the studied thrusts, which represents 10% of the bulk-strain accommodated by the whole reentrant for this timespan, is calculated. In spite of the marginal appearance of this figure, this deformation rate is attributed to 7

We use Global Navigation Satellite Systems observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth. The velocity field exhibits an asymmetric velocity gradient on either side of the EPF. We use five different approaches to explore possible models to explain this asymmetry. First, we infer a 1.6 km locking depth using a classic elastic half-space dislocation model. Second, we infer a 1.5 km locking depth and a 0.33 asymmetry coefficient using a heterogeneous asymmetric model, including contrasting material properties on either side of a vertical fault, suggesting that the igneous-metamorphic terranes on the northern side are ~2 times more rigid than the sedimentary southern side. Third, we use a three-dimensional elastostatic model to evaluate the presence of a compliant zone, suggesting a 30% reduction of rigidity in the upper 3 km at the depth of a 1 to 5 km wide fault zone. Fourth, we evaluate the distribution of fault slip, revealing a widespread partial creep pattern in the eastern upper segment, while the upper western segment exhibits a partially locked area, which coincides with the rupture surface of the 1797 and 1929 earthquakes. To supplement these models, we upgrade the previously published displacement simulation method using nonvertical dislocations with data acquired between 2003 and 2013. The localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity.

Three main Cenozoic thrusts at the front of Northwestern Himalaya have accommodated most of the India–Eurasia convergence across the belt over the last million years and produced the present relief. Their recent tectonic activity is poorly known because of the long period of inaccessibility of the Jammu and Kashmir state, and because the latest and only large earthquake recorded in the region occurred in 1555 AD. We show where the deformation is localized during the Late-Quaternary, and determine shortening rates across the structures by analyzing the geometry and chronology of geomorphic markers. The Main Boundary Thrust in this region ceased moving at least ∼30 ka ago. On the contrary, the more external Medlicott–Wadia Thrust and Main Frontal Thrust, both merging at depth on the sub-flat detachment of the Main Himalayan Thrust, exhibit hectometric-scale deformations accumulated during the last thousands of years. The total shortening rate absorbed by these faults over the last 14–24 ka is between 13.2 and 27.2 mm/yr ( 11.2 ± 3.8 and 9.0 ± 3.2 mm / yr , respectively). Part of this deformation may be associated to the geometry of the Chenab reentrant, which could generate an extra oblique component. However, the lower bound of our shortening rates is consistent with previously determined geodetic rates. Active deformation on these structures follows an in-sequence/out-of-sequence pattern, with breaking of both ramps being possible for earthquakes triggered on the main detachment.

15 pages; International audience; The recent activity of the Medlicott-Wadia Thrust (MWT) is investigated by geomorphic and tectonic studies in the Riasi zone, south of the Pir Panjal range (India, Jammu-Kasmir state of western Himalaya). In the Riasi area, the MWT forms a splay of five faults that dip northward. The recent activity of the splay is quantified using a set of deformed Quaternary alluvial units. The central branch of the thrust splay moved Precambrian limestones above Quaternary sediments and is sealed by 36 ± 3 ka (youngest OSL age) deposits. The other branches offset the top of a 15 ± 1 ka (youngest OSL age) alluvial fan by 180 to 120 m; the two southernmost branches form 17–34 m high non-cylindrical scarps and the two northernmost branches also offset the fan by ∼8 m and ∼54 m, respectively. A balanced cross-section parallel to the N210°E thrust motion suggests that the sequence of activity is complex: an in-sequence propagation is found for the three southern Tea, Scorpion and Rain faults and an out-of-sequence reactivation for the northern Pillar fault. Furthermore, several thrusts simultaneously activated for intervals of a few thousand years, whereas others are episodically inactive. Nearly 10 mm/yr of India-Eurasia convergence is regularly absorbed by the MWT, a value greater than the one estimated for the western segment of the MWT affected by the 2005 Kashmir earthquake, where the thrust tectonics interacts with the complex kinematics of the syntax. This work indicates that the MWT is very active and might be related to thick-skinned tectonics in the western Himalaya.

16 pages; International audience; The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochronological methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces at its hangingwall are identified. The terraces have been dated by combining Optically Stimulated Luminescence (OSL) on fine-grained deposits and cosmogenic-nuclide dating (10Be) on sandstone pebbles sampled along depth profiles throughout the alluvial units. Three major allostratigraphic units were defined with upper surface ages estimated at ~ 4, ~ 15, and 36 ± 3 ka; the two older allostratigraphic units are encased terraces at the hangingwall but superposed sedimentary units at the footwall. They are related to phases of elevation of the river level (respectively 30 and 60 m) at ~ 36–38 and 14–15 ka and to a phase of extensive lateral incision before ~ 4 ka. These units present vertical offsets induced by the MWT of 50, 190, and 375 m, respectively. By taking the aggradation/incision rates at the footwall of the MWT into account, we found that the uplift of the hangingwall remains uniform since 36 ka, with a value of ~ 10 mm/yr. Therefore, the aggradation/incision events observed in the Riasi area cannot be ascribed to variations in the tectonic rates and are most likely driven by climatic fluctuations. The high uplift rate is possibly local and related to the Chenab recess, which affects the Himalayan frontal structure. Our results indicate that the MWT is an active growth fault, and one of the main emergences of the active Indian/Asian plate boundary in Western Himalaya.

A major question about the Himalaya remains open: does a great earthquake (like the Mw ~ 8.1 1934 earthquake) release all the strain stored by the Tibet–India convergence during the preceding interseismic period and only that strain, or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events? To consider this question, the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of Kathmandu, trenches through surface ruptures, isoseismal damage mapping, seismites, and the instrumental record. In the Kathmandu basin, the location of the epicenter of the 1934 earthquake was determined from the arrival of high-energy P-waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth. The epicenter of the Mw ~ 7.6 1833 earthquake can therefore be determined analogously from dike orientation, and its location to the NE of Kathmandu indicates an overlap with the Mw ~ 8.1 1934 rupture. The 1934 earthquake released strain not released by the 1833 earthquake. Comparison of the historical records of earthquakes in Kathmandu with 14C ages from paleo-seismic trenches along the Himalayan front suggests that: (1) the 1344 Kathmandu event ruptured the surface as far away as Kumaon and was therefore a giant Mw ≥ 8.6 earthquake; and (2) the 1255 event that destroyed Kathmandu is attested by surface ruptures in central and western Nepal and by seismites in soft sediment as far away as Kumaon. Geometric and rheologic controls for the different types of ruptures during the medium (Mw ~ 7), great (Mw ≥ 8), and giant (Mw > 8.4) earthquakes are illustrated in structural cross-sections. It is found that the epicenters of great Himalayan earthquakes are located on the basal thrust farther north or close to the locked zone, which is defined from geodetic measurements of regional deformation during the interseismic period; this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes, the extent of which depends on the dip of the Main Himalayan Thrust. The succession of the great earthquakes during the last millennium has released all the 20-m millennial Himalayan convergence; even in the central seismic gap which has been locked since 1505, the millennial seismic release rate is close to the convergence rate. Nonetheless, no evidence of a succession of characteristic earthquakes has been found: the ~ 1100, 1833, and 1934 earthquakes in the eastern Himalaya are characterized neither by constant displacement nor by constant recurrence. Furthermore, some great earthquakes do not release all the strain elastically stored by the Himalayan and Tibetan upper crust: after the 1255 event, there was still the potential for a slip of several meters for the Mw ~ 8.1 1505 event. This suggests a rather random release of seismic energy; great earthquakes could occur anytime and in any part of the central Himalaya. Furthermore, a future giant earthquake of Mw ≥ 8.6 cannot be excluded.

International audience; The coseismic surface displacement field and slip distribution at depth due to the Kashmir earthquake (Mw = 7.6, 2005) have been analysed by different authors using subpixel correlation of synthetic aperture radar (SAR) images and optical images, teleseismic analysis, GPS measurements, as well as in situ field measurements. In this paper, first, we use 23 sets of measurement from subpixel correlation of SAR images and differential interferometry to retrieve the 3-D coseismic surface displacement field. The obtained horizontal and vertical components along the fault trace are then compared, respectively, to equivalent measurements obtained from subpixel correlation of two optical ASTER images and in situ field measurements. Second, the coseismic fault geometry parameters and slip distribution at depth are estimated. In addition to the one segment slip model as reported in previous work, a two segments slip model that better fits the surface fault break is proposed. The improvement of the two segments slip model in interpreting the measured displacement field is highlighted through comparison of residuals of both slip models. Taking advantage of differential interferometry measurements that provide precise and continuous information in the far field of the fault, firstly, a wedge thrust according to Bendick et al. to the Northwest of the main rupture built on our two segments model is tested. According to the obtained results, the residual of the two segments main rupture plus wedge thrust model is slightly smaller than the residual of the two segments model to the Northwest of the Balakot-Bagh fault. Secondly, we test the sensitivity of our slip model to the presence of slip along a décollement as evidenced by Jouanne et al. through post-seismic analysis. The results indicate that the estimations of the coseismic displacement field and slip distribution in this paper are not significantly biased by such post-seismic displacement and that most coseismic displacement is located on a ∼40° NE-dipping fault, as previously reported.

Current tectonics of Albania is documented by neotectonics evidences and by a large number of medium size earthquakes. Focal mechanisms suggest a current shortening across the external Albanides whereas internal Albanides are affected by extension with direction varying from E–W to N–S extension. To investigate the kinematics of Albanides, we integrate continuous and episodic GPS velocity measurements with focal mechanisms of the regional centroid moment tensor catalog. This study has allowed distinguishing the followings: 1) western Albania affected by southwestward motions relative to Apulia microplate, the foreland of Albanides, illustrating the ongoing collision of external Albanides; 2) the inner Albanides affected by a southward motion with a southward increase, relative to both Apulia and stable Eurasia. Active thrusts and backthrusts of external Albanides are segmented by strike-slip faults; the fault between the external Albanides and the Ionian zone appears to be particularly active. The fault zone forming the boundary between Dinarides and Albanides, is identified as the northern limit of an area including Albania and western Greece, affected by a clockwise rotation relative to Apulia and also the northern limit of the area (inner Albanides, Macedonia, Bulgaria) affected by southward motion relative to Apulia and stable Eurasia. The ENE–WSW transverse fault zone in Central Albania and western Macedonia (Diber-Elbasani fault) appears to be mainly affected by a moderate extension. CGPS data confirm that the external-inner Albanides transition is the western border of the domain (inner Albania, northern Greece, Macedonia, Bulgaria) affected by southward displacements relative to stable Eurasia and Apulia, whereas the fault zone forming the boundary between Dinarides and Albanides constitutes probably its northern limit.

International audience; Soft-sediment deformation structures have been analyzed at six sites of the Kathmandu valley. Microgranulometric study reveals that silty levels (60 to 80% silt) favor the development of soft-sediment deformation structures, while sandy levels (60 to 80% sand) are passively deformed. Nonetheless well sorted sand levels (more than 80% sand) generate over-fluid pressure during compaction if located beneath a silty cap, leading to fluidization and dike development. 3-D geometry of seismites indicates a very strong horizontal shearing during their development. Using a physical approach based on soil liquefaction during horizontal acceleration, we show that the fluidization zone progressively grows down-section during the shaking, but does not exactly begin at the surface. The comparison of bed-thickness and strength/depth evolution indicates three cases: i) no soft-sediment deformation occurs for thin (few centimeters) silty beds; ii) the thickness of soft-sediment deformation above sandy beds is controlled by the lithological contrast; iii) the thickness of soft-sediment deformation depends on the shaking intensity for very thick silty beds. These 3 cases are evidenced in the Kathmandu basin. We use the 30 cm-thick soft-sediment deformation level formed during the 1833 earthquake as a reference: the 1833 earthquake rupture zone extended very close to Kathmandu, inducing there MMI IX-X damages. A 90 cm-thick sediment deformation has therefore to be induced by an event greater than MMI X. From a compilation of paleo and historic seismology studies, it is found that the great (M ~ 8.1) historical earthquakes are not characteristic of the greatest earthquakes of Himalaya; hence earthquakes greater than M ~ 8.6 occurred. Kathmandu is located above one of the asperities that laterally limits the extent of mega-earthquake ruptures and two successive catastrophic events already affected Kathmandu, in 1255 located to the west of this asperity and in ~ 1100 to the east.

International audience; The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic-stratigraphic units were identified in the upper ~ 200 m of the sedimentary infill. Detailed seismic-stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.

International audience; We have used high resolution seismic imaging to detect and characterize the recent deformation recorded by the Quaternary sediments of Le Bourget Lake. The last glacial episodes (MIS 6a and 2, i.e. Riss and Würm) scoured out an elongated over-deepened basin to more than 300 m below the present lake level and the basin accumulated 150 m of post-LGM to Holocene sediments. The well-stratified character of the infill is locally disturbed by tectonic deformations and gravity reworking. A northern fault zone, in continuation with the left-lateral strike-slip Culoz Fault, is imaged within the Holocene and Late Glacial accumulations. A southern fault zone is also detected, which can be related to the sublacustrine continuation of a much smaller fault affecting the Jura alpine foreland: the Col du Chat left lateral strike-slip fault. Different generations of fractures have been identified in the lake, allowing correlation and mapping. In pre-Quaternary substratum, the Culoz Fault has a N 160° orientation. Within the post-LGM sediments, fractures related to the Culoz Fault have an orientation between N135° and 95°. A Cloos model (1932) is thus proposed to explain the observed pattern of lacustrine deformations. The calculated horizontal slip rate for Culoz Fault during Holocene is about 1.3 mm.yr-1, and for the Col du Chat fault is around 0.6 mm.yr-1.

The Boconó Fault system is a major active tectonic feature accommodating an important part of the dextral relative motion between the Caribbean Plate and northern South-America. The main trace follows an axial valley running SW-NE within the Mérida Andes (northwestern Venezuela), and crosscuts a series of moraines related to late Pleistocene glaciers developments and retreats, at an altitude between 2600 and 5000 m. Several lakes were generated after the last retreat (between the Late Glacial Maximum –LGM– and the Younger Dryas re-advance), dammed by lateral and frontal moraines. Among them, the Los Zerpa moraine system yielded rich outcrops ranging from an upstream very coarse torrential to deltaic fill, to a downstream clayey-silty horizontal laminated lacustrine accumulation; a fore-set-type heterogeneous “prograding” body links the two sets. The whole system, as well as the surrounding moraines, underwent successive major earthquakes during the Late Glacial/lower Holocene period as evidenced by co-seismic scarps in the moraines, migrations of the outlet, and associated sagponds. Besides active faulting affecting both the moraines and the sedimentary fill, the latter –main purpose of our detail study– exhibits various evidence of strong disturbances which we relate to seismic shaking, such as: i) successive unconformities with co-seismic slips along fractures in the coarse proximal sediments; ii) successive dip changes, discontinuities, and slumps in the foreset-like set; iii) slumps with basal liquefaction, syn-sedimentary fractures, and instantaneous re-sedimentation in the fine-grained laminated accumulation. Lateral (temporal) correlations are established between the successive disturbances detected in the three situations; in turn, these sedimentary events are correlated with seismic activity of the Boconó Fault main trace. Thus, the whole paleo-lake may be considered as a natural seismograph which worked during several thousands years, after the end of the LGM and during early Holocene.

International audience; The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N-S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N-E) of 4-7 mm in 1993 and 2-3 mm in 1998 and compare at the 3-5-mm level in position and 2-mm/ yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N-S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/ or by rotations of Mediterranean microplates. Also, E-W velocity components analysis supports the idea that E-W extension exists, as already suggested by recent structural and seismotectonic data interpretation.

International audience; Grimsvötn Volcano is the most active volcano in Iceland, and its last three eruptions were in 1998, 2004, and 2011. Here we analyze the displacement around Grimsvötn during these last three eruptive cycles using 10 GPS stations. The observed displacements in this region generally contain a linear component of tectonic and glacio-isostatic origin, in agreement with the previously estimated values of plate motions and vertical rebound. Larger amplitude deformation observed close to Grimsvötn at the GFUM continuous GPS station clearly reflects a major volcanic contribution superimposed on a tectonic component. We estimate and subtract the tectonic trend at this station using regional observed displacement. The direction and pattern of the residual volcanic displacement (for coeruptive and intereruptive periods) are consistent for all three of these eruptive cycles. The post eruptive inflation is characterized by an exponential trend, followed by a linear trend. In this study, we explain this temporal behavior using a new analytic model that has two connected magma chambers surrounded by an elastic medium and fed by a constant basal magma inflow. During the early post eruptive phase, pressure readjustment occurs between the two reservoirs, with replenishment of the shallow chamber from the deep chamber. Afterward, due to the constant inflow of magma into the deep reservoir, the pressurization of the system produces linear uplift. A large deep reservoir favors magma storage rather than surface emission. Based on displacement measured at GFUM station, we estimate an upper limit for the radius of the deep reservoir of ∼10 km.

We formed interferograms of ERS-SAR scenes covering the area of Krafla (N. Iceland) with time span values of up to six years (1992–1998). Our data reveals a steady deformation rate at Krafla and within its fissure swarm, with values reaching +2.1 cm/y in the ground to satellite direction, at the volcano. The area affected by deformation extends 20 km both north and south of the volcano. The best fit dislocation model consists of sills, to the north and south of the volcano, and a magma chamber, located below the volcano, all of them undergoing contraction.

The kinematics of the present-day deformation in the western Alps is still poorly known, mostly because of a lack of direct measurements of block motion and internal deformation. Geodetic measurements have the potential to provide quantitative estimates of crustal strain and block motion in the Alps, but the low expected rates, close to the accuracy of the geodetic techniques, make such measurements challenging. Indeed, an analysis of 2.5 years of continuous GPS data at Torino (Italy), Grasse (France), and Zimmerwald (Switzerland), showed that the present-day differential motion across the western Alps does not exceed 3 mm/yr [Calais, 1999]. Continuous measurements performed at permanent GPS stations provide unique data sets for rigorously assessing crustal deformation in regions of low strain rates by reducing the amount of time necessary to detect a significant strain signal, minimizing systematic errors, providing continuous position time series, and possibly capturing co- and post-seismic motion. In 1997, we started the implementation of a network of permanent GPS stations in the western Alps and their surroundings (REGAL network). The REGAL network mostly operates dual frequency Ashtech Z12 CGRS GPS stations with choke-ring antennae. In most cases, the GPS antenna is installed on top of a 1.5 to 2.5 m high concrete pilar directly anchored into the bedrock. The data are currently downloaded once daily and sent to a data center located at Geosciences Azur, Sophia Antipolis where they are converted into RINEX format, quality checked, archived, and made available to users. Data are freely available in raw and RINEX format at http://kreiz.unice.fr/regal/. The GPS data from the REGAL network are routinely processed with the GAMIT software, together with 10 global IGS stations (KOSG, WZTR, NOTO, MATE, GRAZ, EBRE, VILL, CAGL, MEDI, UPAD) that serve as ties with the ITRF97. We also include the stations ZIMM, TORI, GRAS, TOUL, GENO, HFLK, OBER because of their tectonic interest. We obtain long term repeatabilities on the order of 2-3 mm for the horizontal components, 8-10 mm for the vertical component. Using a noise model that combines white and coloured noise (flicker noise, spectral index 1), we find uncertainties on the velocities ranging from 1 mm/yr for the oldest stations (ZIMM, GRAS, TOUL, TORI, SJDV) to 4-5 mm/yr for the most recently installed (CHAT, MTPL). Station velocities obtained in ITRF97 are rotated into a Eurasian reference by substracting the rigid rotation computed from ITRF97 velocities at 11 central European sites located away from major active tectonic structures (GOPE, JOZE, BOR1, LAMA, ZWEN, POTS, WETT, GRAZ, PENC, Effelsberg, ONSA). The resulting velocity field shows residual motions with respect to Eurasia lower than 3 mm/yr. We obtain at TORI, in the Po plain, a residual velocity of 2.3+ or -0.8 mm/yr to the SSW and a velocity of 1.9+ or -1.1 mm/yr at SJDV, on the Alpine foreland. These results indicate that the current kinematic boundary conditions across the western Alps are extensional, as also shown by the SJDV-TORI baseline time series. We obtain at MODA (internal zones) a residual velocity of 1.2+ or -1.2 mm/yr to the SSE. The MODA-FCLZ baseline show lengthening at a rate of 1.6+ or -0.8 mm/yr. These results are still marginally significant but suggest that the current deformation regime along the Lyon-Torino transect is extension, as also indicated by from recent seismotectonic data. It is in qualitative agreement with local geodetic measurements in the internal zones (Briancon area) but excludes more than 2.4 mm/yr of extension (FCLZ-MODA baseline, upper uncertainty limit at 95% confidence). Our results indicate a different tectonic regime in the southern part of the western Alps and Provence, with NW-SE to N-S compression. The GRAS-TORI baseline, for instance, shows shortening at a rate of 1.4+ or -1.0 mm/an. This result is consistent with seismotectonic data and local geodetic measurements in these areas. The Middle Durance fault zone, one of the main active faults in this area, is crossed by the GINA-MICH baseline, which shows shortening at a rate of 1.0+ or -0.8 mm/an. This result is only marginally significant, but confirms the upper bound of 2 mm/yr obtained from triangulation-GPS comparisons. The REGAL permanent GPS network has been operating since the end of 1997 for the oldest stations and will continue to be densified. Although they are still close to or within their associated uncertainties, preliminary results provide, for the first time, a direct estimate of crustal deformation across and within the western Alps.

The REGAL permanent GPS network currently consists of 12 GPS stations covering the Western Alps and their foreland. Preliminary results indicate ( i ) residual velocities with respect to Eurasia lower than 3 mm·yr –1 , ( ii ) extensional kinematic boundary conditions along the Lyons–Turin transect and extensional strain regime in the central part of the Western Alps, and ( iii ) north–south to NW–SE compression in the southern Alps and Provence. These results are still preliminary and marginally significant, given the associated uncertainties. They are however consistent with the most recent seismotectonic results published in these areas.

The current tectonics of north Iceland are characterised by max M 6–7 earthquakes in the transform zone between the northern rift zone and the Kobleinsey Ridge. The last rifting period (1975–1984) was associated with an opening of up to 9 m along the Krafla fissure swarm. This period was followed by the disappearance of microseismicity along the eastern part of Husavik-Flatey Fault, the main structure of the transform zone. A GPS network was occupied in 1995 and again in 1997 to study present-day deformation on both sides of the on-land part of HFF and around its junction with the northern rift zone. The main deformational features observed are: (1) in Tjornes, the HFF is locked above the ductile/brittle boundary below which ductile creep is occurring, and (2) aseismic opening along the Theystareykir and Krafla fissure swarms and along a N 120°E superficial fault that marks the southern boundary of Tjornes.

Determination of relative movements between the alpine foreland and the External Crystalline Massif is a key-point for the understanding of the present-day tectonics of the western Alps. In this study we try to test the continuity of the present-day tectonics with the Mio-Pliocene deformation. In particular, we will test if the present-day displacements are localized along the thrusts of the Jura Mountains, or along a blind thrust in the Bas Dauphine Molasse Basin. Definition of relative movements is achieved by several methods, including a comparison of two high precision leveling networks to estimate vertical displacements, horizontal deformation measurements performed by triangulation/triangulation and triangulation/GPS comparison, in situ stress measurements performed in the different tectonic units and geomorphologic observations that constrain the location and the magnitude of the Quaternary deformation. Comparison of leveling data demonstrates: (1) an uplift of the southern Bas Dauphine Molasse Basin relative to its northern part (0.8 mm/year), also revealed by geomorphologic analysis, (2) a significant uplift of the most external jurassian anticlines (0.8 to 2 mm/year), also recorded by the deformation of a paleo-river bed, and (3) an important uplift (up to 2 mm/year) of the Subalpine Massifs. The horizontal strain estimated from comparison of horizontal geodetic data (triangulation, GPS) shows (1) a NW–SE directed shortening between the eastern Chartreuse Massif and the Bas Dauphine Molasses Basin (approximately 3 mm/year), (2) an E–W-directed shortening in the Jura Mountains (approximately 4–3 mm/year) and (3) a dextral strike-slip motion consistent with focal mechanisms along a NNE–SSW direction between the eastern Chartreuse Massif and the eastern Belledonne Massif. These data reveal a present-day strain partitioning between the Belledonne External Crystalline Massif and the Bas Dauphine Molasses Basin. The westward motion of the Subalpine Massifs is partitioned along two southern jurassian thrust-folds, and a dextral NNE–SSW strike-slip shear zone between the Chartreuse Massif and the Belledonne Massif. This strain partitioning is also accompanied by a stress partitioning between the alpine foreland and the External Crystalline Massifs.

Active deformation in the southern part of the Rhinegraben, studied by comparing leveling measurements, is characterized by vertical movements. Upward movements greater than 1 mm·y −1 have been measured near Mulhouse and Selestat. Smaller rates of uplift averaging 1 mm·y −1 were also observed above some groups of salt plugs striking NW-SE. Both types of vertical uplift are compatible with the regional stress field. The movements may be associated with the reactivation of NE-striking Variscan thrusts and with continuing upward growth of those salt plugs that are perpendicular to the minimum horizontal stress.

International audience; Fluvial terraces of Shkumbin, Devoll, Osum and Vjosa rivers (southern Albania and northwestern Greece) are studied in order to quantify the vertical slip rates of the large active faults of the Dinaric-Albanic-Hellenic Alpine fold belt. The spatial and temporal variations of the incision rates along these rivers were estimated from the geomorphological mapping of the Quaternary sediments, the geometry and the dating of the terraces. Eleven terraces levels were identified in Albania from 68 geochronological ages already published or acquired for this work. The five lower terraces of the four studied rivers are well dated (10 new and 23 already published ages). These terraces are younger than 30 ka and their remnants are numerous. Their restoration allows estimating the regional trend of incision rate and the identification of local shifts. We argue that these shifts are linked to the active tectonics when they coincide with the faults already mapped by previous authors. Vertical slip rates for eight active faults in southern Albania are thus estimated for the last 19 ka and vary from ~0.1 to ~2 mm/a. The Lushnje Tepelene Thrust, that extends more than 120 kilometers, has a throw rate that varies from 0.2 to 0.8 mm/a, whereas the active faults of the extensional domain are segmented but are very active, with throw rates reaching locally 2 mm/a.

The positions of 20 geodetic points surveyed in 1946-1952 by the Institut Geographique National in the Grenoble area (western Alps) were remeasured in 1993-1994 using GPS. We evaluate the displacements of the common points of the networks between the two surveys, and calculate the strain-rate tensors for different sets of three adjacent points. The significant N70° shortening direction observed at the boundary of the Belledonne and Taillefer massifs suggests that the dextral strike-slip motion between the External Crystalline Massifs (ECM) and the Subalpine domain is still active. Geological evidence suggests that this deformation, which is compatible with the few focal mechanisms available for the area, occurred throughout the late Neogene. Our data also suggest a roughly 3-5 mm yr−1 active shortening concentrated at the external front of the Subalpine chains. This thrust motion results in a principal axis of compression orientated N130°, oblique to the direction of shortening observed in the ECM. This change in direction is also seen in in situ stress measurements. This motion may mark the southward continuation of the active fault observed in the Jura mountains by Jouanne, Menard & Darmendrail (1995).

Two high-precision leveling networks were successively surveyed in France, the NGF, measured during the 1886–1907 period, and the IGN69, measured from 1965 to 1979. The accuracy of these levelings (standard deviation of 1.8mm/√km to 3.8mm/√km) allows us to compute the vertical displacements of the benchmarks between two different eras. The results indicate the occurrence of discrete zones of uplift and subsidence: (1) a regional uplift (up to 1.4 mm/yr) of the Subalpine Massifs; (2) an important uplift of the internal Jura (up to 2 mm/yr); (3) a relative subsidence of the southern part of the Jura (0.8 mm/yr); and (4) a relative subsidence of the Bresse Basin with respect to the external Jura. Comparing the spatial distribution of zones of uplift and their respective vertical displacement rates with a regional structural cross section leads to the conclusion that present-day uplift of the Belledonne and Bornes Massifs and of the internal parts of the Jura Mountains, can be explained by crustal shortening along a major basement-involving thrust fault. This fault ramps up under the Bornes Massif from a depth of 12 km to 7 km, turns into a flat under the Molasse Basin, ramps up to the top of the basement at the north-eastern margin of the internal Jura Mountains, and reaches the surface in the external Jura. The Saleve ramp-anticline is carried by a bifurcation of this thrust. Horizontal displacement rates of 6 mm/yr at the Bornes ramp, 2 mm/yr at the Saleve ramp, and 4 mm/yr at the internal Jura ramp have been determined by inversion of profiles of uplift rates. Whether this basement-involving thrust fault was already active during the Miocene main folding phase of the Jura Mountains or whether it was activated only during Pliocene-Pleistocene times is subject to debate.

We present a new kinematic and strain model of an area encompassing the Calabrian and Hellenic subduction zones, western Anatolia and the Balkans. Using Haines and Holt's (1993) method, we derive continuous velocity and strain rate fields by interpolating geodetic velocities, including recent GPS data in the Balkans. Relative motion between stable Eurasia and the western Aegean Sea is gradually accommodated by distributed N-S extension from Southern Balkans to the Eastern Corinth Gulf, so that the westward propagation of the North Anatolian Fault (NAF) throughout continental Greece or Peloponnesus is not required. We thus propose that the NAF terminates in north Aegean and that N-S extension localized in the Corinth Gulf and distributed in Southern Balkans is due to the retreat of the Hellenic slab. The motion of the Hyblean plateau, Apulia Peninsula, south Adriatic Sea, Ionian Basin and Sirte plain can be minimized by a single rigid rotation around a pole located in the Sirte plain, compatible with the opening the Pelagian rifts (2–2.5 mm/yr) and seismotectonics in Libya. We interpret the trenchward ultraslow motion of the Calabrian arc (2–2.5 mm/yr) as pure collapse, the Calabrian subduction being now inactive. In the absolute plate motion reference frame, our modeled velocity field depicts two toroidal crustal patterns located at both ends of the Hellenic subduction zone, clockwise in NW Greece and counter-clockwise in western Anatolia. We suggest the NW Greece toroidal pattern is the surface expression of a slab tear and consequent toroidal asthenospheric flow.

SUMMARY The change of the coordinates of 44 geodetic points between two surveys, epochs 1930-36 and 1979-84 are studied. The discussion is supported by strain rate tensors and angular shear rates for different sets of three adjacent points as well as by calculated displacements together with their confidence ellipses. The southern Jura mountains may undergo a relatively homogenous pattern of deformation characterized by a roughly east-west to NE-SW compression and by a significant westward motion (5 mm yr-') relative to the frontal ha mountains. This deformation would be compatible with the few focal mechanisms of earthquakes available for this area. A displacement of nearly 2 cm yr-l affected a geodetic point north of Annecy. Unfortunately, this point is the only one that shows such a movement, we cannot exclude a local displacement of this benchmark.

22p.; International audience; The 8 October 2005 Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and August 2006, in March and December 2007, and in August 2008 and 2009. Two hypotheses were tested: post-seismic displacements controlled by viscous relaxation of the lower crust or by afterslip along a flat north of the ramp affected by the main shock. A single Newtonian viscosity for the different periods cannot be determined by numerical simulations of viscous relaxation, which may indicate that the viscosity of the lower crust is non-Newtonian or that viscous relaxation does not control postseismic displacements. Numerical simulations using dislocations in a uniform elastic half-space indicate afterslip north of the ramp of the earthquake along a flat connected to the ramp. Slip along the northwestern portion of the flat accrued to about 285 mm between November 2005 and August 2006, while slip along the southeastern portion accrued to 130 mm over the same time period. Residual misfit of the observed and predicted displacements clearly indicated that afterslip is a better explanation for the observations than the hypothesis of viscous relaxation. The time evolution of the afterslip was found to be consistent with that predicted from rate-strengthening frictional sliding.

International audience; The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault. Velocities simulations using dislocations in an elastic half-space show: (1) the concentration along the El Pilar Fault of the whole Caribbean-South America relative displacement, (2) the existence of an important component of aseismic displacement along the upper part of the El Pilar Fault. Between 12 km depth and the surface, only 40% of displacement is locked for the western segment and 50% for the eastern segment. This last phenomenon may be related to the existence of serpentinite lenses along the fault zone as observed for segments of San Andreas and North Anatolian faults.

In Albania, the Osum and Vjoje rivers cross the active graben system and the active frontal thrust system of the Albanides. The effects of climatic and geodynamic forcing on the development of these two rivers were investigated by the means of field mapping, topographic surveying and absolute exposure-age dating. We established the chronology of terraces abandonment from the compilation of new dating (14C andin situproduced10Be) and previously published data. We identified nine fluvial terraces units developed since Marine Isotope Stage 6 up to historic times. From this reconstituted history, we quantified the vertical uplift on a time scale shorter than the glacial climatic cycle. Regional bulging produces an overall increase of the incision rate from the west to the east that reaches a maximum value of 2.8 m/ka in the hinterland. Local pulses of incision are generated by activation of normal faults. The most active faults have a SW–NE trend and a vertical slip rate ranging from 1.8 to 2.2 m/ka. This study outlines the geodynamic control in the development of rivers flowing through the Albanides on the scale of 103–105ka.

We have conducted a systematic inversion of striated fault planes throughout northern Pakistan in order to better depict the temporal and spatial variations in stress patterns. Two domains are evidenced at a regional scale, separated by the active Raikhot fault, the western boundary of the Nanga Parbat spur. West of this fault, a wrench-type stress field with σ1 axis oriented around N–S predominates in the Karakorum and in Kohistan. It predates Pliocene-Quaternary exhumation of Nanga Parbat and corresponds to the Miocene or earlier regional stress field related to Indian-Asian convergence. East of the Raikhot fault, compression parallel to the belt accounts for initiation of the Nanga Parbat anticlinorium after 5 Ma. It is followed by predominant post-2 Ma extension, both parallel to the belt and NNE–SSW oriented. Thus, in the N–W Himalayan syntaxis, multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt. Such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence.

International audience; Lake Shkodra (northern Albania, southern Montenegro) is a large (45 km length, 15 km width) and shallow (5 m mean depth) lake, developed on a mainly karstic carbonate substratum. Its recent sedimentary fill (mixed calcareous/siliciclastic clayey silts) was analysed through short gravity cores representing five centuries of environmental archive. A combination of high resolution texture analysis (particle size), magnetic susceptibility, carbon content, and radionuclide activity profiles (210Pb, 137Cs, 241Am) permitted us to detect and date environmental changes, such as the Little Ice Age and the 1962–1963 catastrophic floods. Anthropogenic influences on the watershed, such as damming of the Drin River in the late 1970s, also appear to be recorded. Impacts of known strong earthquakes (1905, 1979), however, could not be clearly detected in the sediment record. The potential of the Shkodra lacustrine archive for paleoseismic investigations on long time intervals (such as Holocene) is discussed. This paper is a preliminary contribution to Shkodra Lake's Holocene paleolimnology.

International audience; The current tectonics of North Iceland are characterized by rifting episodes along fissure swarms and by ML 6–7 earthquakes in the transform zone between the northern rift zone and the Kolbeinsey Ridge north of Iceland. The last rifting period (1975–1984) was associated with an average opening of 5 m along the Krafla fissure swarm. Post-rifting deformation has been revealed by GPS investigations in Northern Iceland. A GPS network was occupied in 1997, 1999 and 2002 to quantify present-day displacements and their variation with time, on both sides of the on-land part of the Húsavík–Flatey fault and around the Krafla fissure swarm. The main deformational features observed are: (1) decrease in spreading velocities between the two timespans 1997–1999 and 1999–2002, (2) the existence, south of the transform zone, of a well-defined ∼20–30-km-wide plate boundary where extension dominates, (3) directly adjacent east and west rift shoulders where displacements are close to those observed on the Eurasian and North American plates and (4) a displacement gradient on Tjörnes that could correspond either to elastic deformation related to a currently locked dextral strike-slip fault or to an attenuated post-rifting effect northwest of Krafla.

We analyse geodetically estimated deformation across the Nepal Himalaya in order to determine the geodetic rate of shortening between Southern Tibet and India, previously proposed to range from 12 to 21 mm yr^(−1). The dataset includes spirit-levelling data along a road going from the Indian to the Tibetan border across Central Nepal, data from the DORIS station on Everest, which has been analysed since 1993, GPS campaign measurements from surveys carried on between 1995 and 2001, as well as data from continuous GPS stations along a transect at the logitude of Kathmandu operated continuously since 1997. The GPS data were processed in International Terrestrial Reference Frame 2000 (ITRF2000), together with the data from 20 International GNSS Service (IGS) stations and then combined using quasi observation combination analysis (QOCA). Finally, spatially complementary velocities at stations in Southern Tibet, initially determined in ITRF97, were expressed in ITRF2000. After analysing previous studies by different authors, we determined the pole of rotation of the Indian tectonic plate to be located in ITRF2000 at 51.409±1.560°N and−10.915± 5.556°E, with an angular velocity of 0.483±0.015°. Myr^(−1). Internal deformation of India is found to be small, corresponding to less than about 2 mm yr^(−1) of baseline change between Southern India and the Himalayan piedmont. Based on an elastic dislocation model of interseismic strain and taking into account the uncertainty on India plate motion, the mean convergence rate across Central and Eastern Nepal is estimated to 19 ± 2.5 mm yr^(−1), (at the 67% confidence level). The main himalayan thrust (MHT) fault was found to be locked from the surface to a depth of about 20km over a width of about 115 km. In these regions, the model parameters are well constrained, thanks to the long and continuous time-series from the permanent GPS as well as DORIS data. Further west, a convergence rate of 13.4 ± 5 mm yr^(−1), as well as a fault zone, locked over 150 km, are proposed. The slight discrepancy between the geologically estimated deformation rate of 21 ± 1.5 mm yr^(−1) and the 19 ± 2.5 mm yr^(−1) geodetic rate in Central and Eastern Nepal, as well as the lower geodetic rate in Western Nepal compared to Eastern Nepal, places bounds on possible temporal variations of the pattern and rate of strain in the period between large earthquakes in this region.