Search

Your search keyword '"Helmstetter, Agnès"' showing total 139 results
Start Over Author "Helmstetter, Agnès"
139 results on '"Helmstetter, Agnès"'

1. Unprecedented seismic swarm in the Maurienne valley (2017–2019) observed by the SISmalp Alpine seismic network: operational monitoring and management

Author

Guéguen, Philippe, Janex, Gael, Nomade, Jérôme, Langlais, Mickael, Helmstetter, Agnès, Coutant, Olivier, Schwartz, Stéphane, and Dollet, Cyrielle

Subjects
Alps, Seismic swarm, HypoDD, Belledonne border fault, Seismic risk, Maurienne, Geophysics. Cosmic physics, QC801-809, Chemistry, QD1-999, Geology, QE1-996.5
Abstract

In 2017–2019, a seismic swarm was triggered in the Maurienne valley (French Alps), with more than 5000 events detected by the regional SISmalp network. The population, who asked SISmalp to provide information on the processes and the associated risk, felt many earthquakes. In a post-L’Aquila trial context, we conducted a reflection on the scientific and social operational management of the crisis. The geological and tectonic analysis, the deployment of a temporary seismic network, an automatic double-difference relocation procedure (HypoDD) after clustering earthquakes, as well as the interactions with the population and the risk managers, have been carried out jointly. The length and unpredictability of the sequence complicated crisis management and the relations between local authorities and civil protection. The involvement of SISmalp, beyond its main scientific and observation prerogatives, has contributed to moderate the fears of the population by providing scientific explanations.

Published
2021
Full Text
View/download PDF

3. The RESOLVE project: a multi-physics experiment with a temporary dense seismic array on the Argenti\`ere Glacier, French Alps

Author

Gimbert, Florent, Nanni, Ugo, Roux, Philippe, Helmstetter, Agnés, Garambois, Stéphane, Lecointre, Albanne, Walpersdorf, Andrea, Jourdain, Bruno, Langlais, Mickael, Larman, Olivier, Lindner, Fabian, Sergeant, Amandine, Vincent, Christian, and Walter, Fabian

Subjects
Physics - Geophysics
Abstract

Recent work in the field of cryo-seismology demonstrates that high frequency (>1 Hz) waves provide key constraints on a wide range of glacier processes such as basal friction, surface crevassing or subglacial water flow. Establishing quantitative links between the seismic signal and the processes of interest however requires detailed characterization of the wavefield, which at the high frequencies of interest necessitates the deployment of large and particularly dense seismic arrays. Although dense seismic array monitoring has recently become routine in geophysics, its application to glaciated environments has yet remained limited. Here we present a dense seismic array experiment made of 98 3-component seismic stations continuously recording during 35 days in early spring on the Argenti\`ere Glacier, French Alps. The seismic dataset is supplemented by a wide range of complementary observations obtained from ground penetrating radar, drone imagery, GNSS positioning and in-situ instrumentation of basal glacier sliding velocities and subglacial water discharge. Through applying multiple processing techniques including event detection from template matching and systematic beamforming, we demonstrate that the present dataset provides enhanced spatial resolution on basal stick slip and englacial fracturing sources as well as novel constraints on heterogeneous nature of the noise field generated by subglacial water flow and on the link between crevasse properties and englacial seismic velocities. We finally outline in which ways further work using this dataset could help tackle key remaining questions in the field., Comment: Submitted to Seismological Research Letters on August 11th 2020

Published
2020

7. Afterslip and aftershocks in the rate-and-state friction law

Author

Helmstetter, Agnes and Shaw, Bruce E.

Subjects
Physics - Geophysics
Abstract

We study how a stress perturbation generated by a mainshock affects a population of faults obeying a rate-state friction law. Depending on the model parameters and on the initial state, the fault exhibits aftershocks, slow earthquakes, or decaying afterslip. We found several regimes with slip rate decaying as a power-law of time, with different characteristic times and exponents. The complexity of the model makes it unrealistic to invert for the friction law parameters from afterslip data. We modeled afterslip measurements for the Southern California Superstition Hills earthquake using the complete rate-and-state law, and found a huge variety of model parameters that can fit the observed data. In particular, it is impossible to distinguish the stable velocity strengthening regime (A>B) from the (potentially) unstable velocity weakening regime (B>A and stiffness k

Published
2007

8. Relation between stress heterogeneity and aftershock rate in the rate-and-state model

Author

Helmstetter, Agnes and Shaw, Bruce E.

Subjects
Physics - Geophysics
Abstract

We estimate the rate of aftershocks triggered by a heterogeneous stress change, using the rate-and-state model of Dieterich [1994].We show that an exponential stress distribution Pt(au) ~exp(-tautau_0) gives an Omori law decay of aftershocks with time ~1/t^p, with an exponent p=1-A sigma_n/tau_0, where A is a parameter of the rate-and-state friction law, and \sigma_n the normal stress. Omori exponent p thus decreases if the stress "heterogeneity" tau_0 decreases. We also invert the stress distribution P(tau) from the seismicity rate R(t), assuming that the stress does not change with time. We apply this method to a synthetic stress map, using the (modified) scale invariant "k^2" slip model [Herrero and Bernard, 1994]. We generate synthetic aftershock catalogs from this stress change.The seismicity rate on the rupture area shows a huge increase at short times, even if the stress decreases on average. Aftershocks are clustered in the regions of low slip, but the spatial distribution is more diffuse than for a simple slip dislocation. Because the stress field is very heterogeneous, there are many patches of positive stress changes everywhere on the fault.This stochastic slip model gives a Gaussian stress distribution, but nevertheless produces an aftershock rate which is very close to Omori's law, with an effective p<=1, which increases slowly with time. We obtain a good estimation of the stress distribution for realistic catalogs, when we constrain the shape of the distribution. However, there are probably other factors which also affect the temporal decay of aftershocks with time. In particular, heterogeneity of A\sigma_n can also modify the parameters p and c of Omori's law. Finally, we show that stress shadows are very difficult to observe in a heterogeneous stress context., Comment: In press in JGR

Published
2005
Full Text
View/download PDF

9. Intercluster Correlation in Seismicity

Author

Helmstetter, Agnes and Sornette, Didier

Subjects
Physics - Geophysics
Abstract

Mega et al.(cond-mat/0212529) proposed to use the ``diffusion entropy'' (DE) method to demonstrate that the distribution of time intervals between a large earthquake (the mainshock of a given seismic sequence) and the next one does not obey Poisson statistics. We have performed synthetic tests which show that the DE is unable to detect correlations between clusters, thus negating the claimed possibility of detecting an intercluster correlation. We also show that the LR model, proposed by Mega et al. to reproduce inter-cluster correlation, is insufficient to account for the correlation observed in the data., Comment: Comment on Mega et al., Phys. Rev. Lett. 90. 188501 (2003) (cond-mat/0212529)

Published
2003
Full Text
View/download PDF

10. Bath's law Derived from the Gutenberg-Richter law and from Aftershock Properties

Author

Helmstetter, Agnes and Sornette, Didier

Subjects
Physics - Geophysics
Abstract

The empirical Bath's law states that the average difference in magnitude between a mainshock and its largest aftershock is 1.2, regardless of the mainshock magnitude. Following Vere-Jones [1969] and Console et al. [2003], we show that the origin of Bath's law is to be found in the selection procedure used to define mainshocks and aftershocks rather than in any difference in the mechanisms controlling the magnitude of the mainshock and of the aftershocks. We use the ETAS model of seismicity, which provides a more realistic model of aftershocks, based on (i) a universal Gutenberg-Richter (GR) law for all earthquakes, and on (ii) the increase of the number of aftershocks with the mainshock magnitude. Using numerical simulations of the ETAS model, we show that this model is in good agreement with Bath's law in a certain range of the model parameters., Comment: major revisions, in press in Geophys. Res. Lett

Published
2003
Full Text
View/download PDF

11. Are Aftershocks of Large Californian Earthquakes Diffusing?

Author

Helmstetter, Agnes, Ouillon, Guy, and Sornette, Didier

Subjects
Physics - Geophysics
Abstract

We analyze 21 aftershock sequences of California to test for evidence of space-time diffusion. Aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening. Here, we test an alternative mechanism to explain aftershock diffusion, based on multiple cascades of triggering. In order to characterize aftershock diffusion, we develop two methods, one based on a suitable time and space windowing, the other using a wavelet transform adapted to the removal of background seismicity. Both methods confirm that diffusion of seismic activity is very weak, much weaker than reported in previous studies. A possible mechanism explaining the weakness of observed diffusion is the effect of geometry, including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes., Comment: latex file of 34 pages, 15 postscript figures, minor revision. In press in J. Geophys. Res

Published
2003
Full Text
View/download PDF

12. Importance of direct and indirect triggered seismicity

Author

Helmstetter, Agnes and Sornette, Didier

Subjects
Physics - Geophysics
Abstract

Using the simple ETAS branching model of seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We show that, in this model, the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake. Previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock., Comment: Latex document of 17 pages + 2 postscript figures

Published
2003
Full Text
View/download PDF

13. Foreshocks Explained by Cascades of Triggered Seismicity

Author

Helmstetter, Agnes and Sornette, Didier

Subjects
Physics - Geophysics, Condensed Matter - Statistical Mechanics
Abstract

The observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable. Among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks, the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock, when averaging over many sequences. Using Southern California seismicity, we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes, without arbitrary distinction between foreshocks, aftershocks and mainshocks. We find that foreshocks precursory properties are independent of the mainshock size. This implies that earthquakes (large or small) are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering. The cascades of triggering give rise naturally to long-range and long-time interactions, which can explain the observations of correlations in seismicity over surprisingly large length scales., Comment: 20 pages, 6 figures, minor revision, in press in J. Geophys. Res

Published
2002
Full Text
View/download PDF

14. Is Earthquake Triggering Driven by Small Earthquakes?

Author

Helmstetter, Agnes

Subjects
Physics - Geophysics, Condensed Matter
Abstract

Using a catalog of seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this relation and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that seismicity triggering is driven by the smallest earthquakes, which trigger fewer events than larger earthquakes, but which are much more numerous. We propose that the non-trivial scaling of the number of triggered earthquakes emerges from the fractal spatial distribution of seismicity., Comment: 5 pages, 2 figures

Published
2002
Full Text
View/download PDF

15. How Injection History Can Affect Hydraulic Fracturing-Induced Seismicity: Insights from Downhole Monitoring at Preston New Road, United Kingdom.

Author

Minetto, Riccardo, Helmstetter, Agnès, Edwards, Benjamin, and Guéguen, Philippe

Abstract

In August 2019, a multistage hydraulic fracturing (HF) operation was carried out at Preston New Road, United Kingdom. HF caused abundant seismic activity that culminated with an ML 2.9 event. The seismic activity was recorded by a downhole array of 12 sensors located in a nearby monitoring well. About 55,556 events were detected and located in real time during the operation by a service company. In this study, we first improve the number of detections by applying template matching and later calculate the moment magnitude of the associated earthquakes. Then we show that by separately analyzing the periods during and immediately after injection, distinct patterns can be identified. We observe an increase in the delay and decrease in amplitude of peak seismicity during subsequent phases of injection. After injection, the seismicity decay can be described by the Omori-Utsu law. The decay rate tends to slow with each successive injection, in particular during the later injection stages. In addition, the frequency-magnitude distribution evolves from a tapered distribution (lack of large events) to a bilinear distribution (excess of large events). This evolution is gradual, with the corner magnitude increasing with each injection. We interpret these patterns as the result of the combined effect of two factors: (1) the stimulated volume becoming increasingly aseismic and (2) the gradual increase in its size, which increases the probability of triggered events on preexisting faults. More generally, these patterns suggest that seismic activity during injection is strongly influenced by the injection history and is modulated by local conditions such as stress state, fault structure, and permeability. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

26. Three-dimensional surface velocity variations of the Argentière glacier (French Alps) monitored with a high-resolution continuous GNSS network

Author

Togaibekov, Anuar, primary, Walpersdorf, Andrea, additional, Gimbert, Florent, additional, Vincent, Christian, additional, Helmstetter, Agnès, additional, Six, Delphine, additional, Moreau, Luc, additional, Roldan-Blasco, Juan Pedro, additional, Ott, Laurent, additional, Mercier, Stéphane, additional, Laarman, Olivier, additional, Piard, Luc, additional, Nanni, Ugo, additional, Matthey, Marguerite, additional, Urruty, Benoit, additional, Sue, Christian, additional, Bouvier, Jean-Noël, additional, Radiguet, Mathilde, additional, Romeyer, Olivier, additional, and Mugnier, Jean-Louis, additional

Published
2021
Full Text
View/download PDF

27. A Multi-Physics Experiment with a Temporary Dense Seismic Array on the Argentière Glacier, French Alps: The RESOLVE Project

Author

Gimbert, Florent, primary, Nanni, Ugo, additional, Roux, Philippe, additional, Helmstetter, Agnès, additional, Garambois, Stéphane, additional, Lecointre, Albanne, additional, Walpersdorf, Andréa, additional, Jourdain, Bruno, additional, Langlais, Mickael, additional, Laarman, Olivier, additional, Lindner, Fabian, additional, Sergeant, Amandine, additional, Vincent, Christian, additional, and Walter, Fabian, additional

Published
2021
Full Text
View/download PDF

34. Seismic monitoring in the Gugla rock glacier (Switzerland): ambient noise correlation, microseismicity and modelling

Author

Guillemot, Antoine, Helmstetter, Agnès, Larose, Éric, Baillet, Laurent, Garambois, Stéphane, Mayoraz, Raphaël, Delaloye, Reynald, Guillemot, Antoine, Helmstetter, Agnès, Larose, Éric, Baillet, Laurent, Garambois, Stéphane, Mayoraz, Raphaël, and Delaloye, Reynald

Abstract

A network of seismometers has been installed on the Gugla rock glacier since October 2015 to estimate seismic velocity changes and detect microseismicity. These two processes are related to mechanical and structural variations occurring within the rock glacier. Seismic monitoring thus allows a better understanding of the dynamics of rock glaciers throughout the year. We observed seasonal variations in seismic wave velocity and microseismic activity over the 3 yr of the study. In the first part of our analysis, we used ambient noise correlations to compute daily changes of surface wave velocity. In winter, seismic wave velocities were higher, probably due to refreezing of the permafrost active layer and cooling of the uppermost permafrost layers, leading to increased overall rigidity of the medium. This assumption was verified using a seismic model of wave propagation that estimates the depth of P- and S-wave velocity changes from 0 down to 10 m. During melting periods, both a sudden velocity decrease and a decorrelation of the seismic responses were observed. These effects can probably be explained by the increased water content of the active layer. In the second part of our study, we focused on detecting microseismic signals generated in and around the rock glacier. This seismic activity (microquakes and rockfalls) also exhibits seasonal variations, with a maximum in spring and summer, which correlates principally with an exacerbated post-winter erosional phase of the front and a faster rock glacier displacement rate. In addition, we observed short bursts of microseismicity, both during snowfall and during rapid melting periods, probably due to pore pressure increase.

Published
2020

35. Rayleigh waves in seismic signals of rockfalls

Author

Lévy, C., Helmstetter, Agnès, Amitrano, David, Le Roy, Gaëlle, Guyoton, Fabrice, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), 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]), Géolithe, Géolithe Alpes, Groupe Géolithe, and Lévy, Clara

Subjects
[SDU.STU.AG] Sciences of the Universe [physics]/Earth Sciences/Applied geology, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], [SDU.STU] Sciences of the Universe [physics]/Earth Sciences, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, [SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], rockfall impacts, S-transform, Rayleigh waves, signal processing, [SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology
Abstract

International audience; Seismic signals of rockfalls are usually very complex, as they are the result of superimposed arrivals of wave trains generated by successive impacts and have a low signal-to-noise ratio (SNR). Thus, retrieving information from these signals is usually challenging. Our objective was to apply the signal processing method proposed by Meza-Fajardo et al. (2015) in order to isolate Rayleigh waves from the rest of the signals. We expect to retrieve: 1) a simplified output signal as only Rayleigh waves trains are extracted, 2) the azimuth of incoming Rayleigh waves (e.g., information on the rockfall localisation), 3) an output signal with a better SNR than the original signal as the decrease of energy due to geometrical attenuation is proportional to 1/r (with r the distance of propagation) for Rayleigh waves, and is proportional to 1/r² for body waves. Our work confirms the large presence of surface waves for this type of signals (a fact widely accepted in the literature, without ever being really discussed). Future studies will determine whether the use of Rayleigh waves (rather than the entire seismic signal) improves the localization of rockfalls, especially when using a method specific for surface waves (the Fast Marching Method).

Published
2018

36. Seismic characterization of clay-block ruptures in the Harmalière landslide (French Western Alps)

Author

Fiolleau, Sylvain, Jongmans, Denis, Bièvre, Grégory, Chambon, Guillaume, Helmstetter, Agnès, Lacroix, Pascal, Baillet, Laurent, 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), Erosion torrentielle neige et avalanches (UR ETGR (ETNA)), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), and 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])

Subjects
[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]
Abstract

International audience; Many regions of the world are exposed to landslides in clay deposits, which pose major problems for land man-agement and population safety. The activity of clayey landslides is complex, showing a succession of periods ofinactivity and reactivation phases that can evolve into sudden acceleration and catastrophic slides and/or flows. Theunderstanding of the processes controlling this activity thus requires the continuous monitoring of specific parame-ters. In late June 2016, the Harmalière clayey landslide (located 30 km south of the city of Grenoble, French Alps)was dramatically reactivated at the headscarp after a 35-year long period of continuous but limited activity. Thetotal involved volume, which moved as sliding blocks of various sizes, was estimated to about 3 106 m3. Severalsensors, including seismometers and GNSS stations, were installed immediately at the rear of the main headscarpin early July 2016. They recorded two further rupture events with volumes of a few hundreds of cubic meters in late 2016 and 2 500 m3 in early 2017. These permanent measurements were supplemented by geophysicaland geotechnical data. Complementary records (seismology, meteorology, piezometry, etc.) were provided by datafrom a permanent observatory located a few hundred meters away in the neighbouring Avignonet landslide (RESIF2006). The kinematics of the Harmalière landslide was further characterized by aerial LIDAR and correlation ofSentinel-2 satellite images.This work aims to better understand the rupture mechanism of the sliding blocks at the head-scarp from this exceptional database, analysing the seismic records. For each rupture event, a three-component seismic sensor was located on the collapsed block. The spectral characteristics of the signals (amplitude, frequency, polarization) were analysed, as well as the seismic velocity deduced from noise cross-correlations with two sensors installed, on the block and a few meters away (first rupture). For the first rupture, the 4-month analysis showed a continuous increase in the block natural frequency (from 8 Hz to more than 9 Hz), which seems to be related to meteorological fluctuations. Just before the rupture, a drop in frequency and in the surface wave velocity variation (dV/V) between sensors was observed. For the second rupture, the relationship with meteorological fluctuations is also observed. However, the natural frequency evolution was more difficult to establish, probably because of the numerous small rupture events preceding the main rupture.

Published
2018

39. Towards a standard typology of endogenous landslide seismic sources

Author

Provost, Floriane, primary, Malet, Jean-Philippe, additional, Hibert, Clément, additional, Helmstetter, Agnès, additional, Radiguet, Mathilde, additional, Amitrano, David, additional, Langet, Nadège, additional, Larose, Eric, additional, Abancó, Clàudia, additional, Hürlimann, Marcel, additional, Lebourg, Thomas, additional, Levy, Clara, additional, Le Roy, Gaëlle, additional, Ulrich, Patrice, additional, Vidal, Maurin, additional, and Vial, Benjamin, additional

Published
2018
Full Text
View/download PDF

40. The Forecasting Skill of Physics‐Based Seismicity Models during the 2010–2012 Canterbury, New Zealand, Earthquake Sequence

Author

Cattania, Camilla, primary, Werner, Maximilian J., additional, Marzocchi, Warner, additional, Hainzl, Sebastian, additional, Rhoades, David, additional, Gerstenberger, Matthew, additional, Liukis, Maria, additional, Savran, William, additional, Christophersen, Annemarie, additional, Helmstetter, Agnès, additional, Jimenez, Abigail, additional, Steacy, Sandy, additional, and Jordan, Thomas H., additional

Published
2018
Full Text
View/download PDF

41. The small rock avalanches of January 9 and April 29 – May 07, 2016 from the calcareous NW and NE pillars of the iconic Mont Granier (1933 m a.s.l., French Alps)

Author

Ravanel, Ludovic, Hoblea, Fabien, Astrade, Laurent, Deline, Philip, Amitrano, David, Helmstetter, Agnès, Hantz, Didier, barnave, suzanne, laily, bruno, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), 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]), Office National des Forêts (ONF), and Referent HAL Edytem, Christine Maury

Subjects
[SDE.BE] Environmental Sciences/Biodiversity and Ecology, [SDE.MCG] Environmental Sciences/Global Changes, [SDE.IE]Environmental Sciences/Environmental Engineering, [SHS.GEO] Humanities and Social Sciences/Geography, [SDE.MCG]Environmental Sciences/Global Changes, [SDE.IE] Environmental Sciences/Environmental Engineering, [SDE.ES] Environmental Sciences/Environmental and Society, [SHS.GEO]Humanities and Social Sciences/Geography, [SDE.BE]Environmental Sciences/Biodiversity and Ecology, [SDE.ES]Environmental Sciences/Environmental and Society, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2016

42. The small rock avalanche of January 9, 2016 from the calcareous NW pillar of the iconic Mont Granier (1933 m a.s.l., French Alps)

Author

Ravanel, Ludovic, Amitrano, David, Deline, Philip, Gallach, Xavi, Helmstetter, Agnès, Hoblea, Fabien, Le Roy, Gaëlle, Ployon, Estelle, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), 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]), Université de Picardie Jules Verne (UPJV), European Geosciences Union, and EDYTEM, Océane Giorda

Subjects
[SDE.BE] Environmental Sciences/Biodiversity and Ecology, [SDE.MCG] Environmental Sciences/Global Changes, [SDE.IE]Environmental Sciences/Environmental Engineering, [SHS.GEO] Humanities and Social Sciences/Geography, [SDE.MCG]Environmental Sciences/Global Changes, [SDE.ES] Environmental Sciences/Environmental and Society, [SDE.IE] Environmental Sciences/Environmental Engineering, [SHS.GEO]Humanities and Social Sciences/Geography, [SDE.BE]Environmental Sciences/Biodiversity and Ecology, [SDE.ES]Environmental Sciences/Environmental and Society
Abstract

Poster; On January 9, 2016 at 4:57, inhabitants of the municipality of Entremont-le-Vieux were awakened by the sound ofa large rock collapse detached from the Mont Granier (1933 m, Savoie, France), iconic mountain of the Chartreusemassif located between Chambery and Grenoble. Its north face, a 900-m-high natural geological cross section inUrgonian limestone, Hauterivian marls, Valanginian limestone and Berriasian marls, was affected in 1248 by ahuge collapse (500 million m3) that caused hundreds of fatalities.The SW pillar, shaped in the upper Urgonian limestone, climbed for the first time in 1964 and several times duringthe warm and dry autumn 2015, collapsed throughout its height (180 m) over a width of up to about 85 m witha volume certainly much higher than 100,000 m3. Blocks rolled down the western slope on about 700 m beforestopping in the forest. It is now notched over a hundred meter wide. No infrastructure was affected.The Granier has many predispositions to large instabilities. This is the western remaining part, largely fractured, ofa much eroded perched syncline whose inclination is oriented to the east. Fracturing and orientation of the stratacontributes to pre-cut limestone and marl. The Granier is also a major karstic area: the Granier plateau with itsmultilevel karst network (90 km of galleries explored) is a good model of polyphased karst network. The region isalso frequently affected by small earthquakes but seismicity does not appear to be a triggering factor. Conversely,the collapse has produced an M 2.2 earthquake. Besides rock fatigue related to what has just been mentioned anda vertical or overhanging topography, it is likely that heavy rains of days before the event and after a long periodof drought have unleashed the destabilization.The collapse is not comparable to the historical event of 1248, which had reshaped the entire northern side.However, its dimensions make the January 2016 event one of the major events of recent decades in the limestonewestern Alps. Events of this size are very rare in the currently available rockfall data series.There is now a significant residual risk of falling boulders while a large overhang just formed suggests probablecollapses in the short or medium term, with volumes exceeding 10,000 m3.

Published
2016

43. Le point sur les auscultations (nivellement, extensométrie, GPS, sismicité) autour de l'effondrement minier de Mas Caché (Chartreuse méridionale)

Author

Ménard, Gilles, Hantz, Didier, Helmstetter, Agnès, Hervé, D., Lacroix, Pascal, Rigollet, S., Referent HAL Edytem, Christine Maury, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la Terre (ISTerre), and 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)

Subjects
[SDE] Environmental Sciences, [SDE]Environmental Sciences
Abstract

Le 09/01/2011 un effondrement dans la carrière à ciment Vicat a affecté la commune de St-Martin-le- Vinoux (Sud Charteuse), provoquant des dégâts importants sur plusieurs maisons du hameau de Mas Caché. Suite à l'effondrement affectant des couches très pentées (45° ou plus), plusieurs réseaux de surveillance ont été installés pour suivre les déformations. Il s'agit d'antennes sismiques, d'un réseau de nivellement, de bases extensométriques et de points GPS. Les premiers enseignements de la partie " géodésie " de ce suivi sont présentés ici. - Le suivi en continu d'un point GPS montre une forte composante horizontale vers l'ESE, permettant d'exclure tout glissement de versant. L'affaissement global en surface serait de l'ordre de 30 cm au sommet de la zone. - Du point de vue spatial, le réseau de nivellement a permis de contraindre les limites nord, sud et ouest de la zone d'affaissement (18 ha), limites qui peuvent être mises en correspondance avec les quartiers effondrés de la carrière souterraine (9-10 ha). - Du point de vue temporel la tendance au ralentissement de l'affaissement observée durant les neuf premiers mois (GPS, nivellement partiel, extensométrie) s'est vu perturbée par une accélération durant l'hiver 2011- 2012, accélération qui s'est répétée durant l'hiver 2012-201. Les remesures de l'ensemble du réseau de nivellement montrent toutefois que ce phénomène saisonnier (infiltrations hivernales ?) n'est pas généralisable à toute la zone, avec des secteurs qui ne montent que du ralentissement de l'affaissement.

Published
2013

46. Slider block friction model for landslides: Application to Vaiont and La Clapiere landslides

Author

Helmstetter, Agnès, Sornette, D., Grasso, J.R., Andersen, Jørgen Vitting, Gluzman, S., Pisarenko, A., Laboratoire de Géophysique Interne et Tectonophysique (LGIT), 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)-Laboratoire Central des Ponts et Chaussées (LCPC)-Centre National de la Recherche Scientifique (CNRS), 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), 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)-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)

Subjects
friction law, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], rupture, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2004
Full Text
View/download PDF

48. Statistical analysis of rockfall volume distributions: implications for rockfall dynamics

Author

Dussauge, C., Grasso, Jean-Robert, Helmstetter, Agnès, 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), 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 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), Institut des Sciences de la Terre [2011-2015] (ISTerre [2011-2015]), 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)-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)-Laboratoire Central des Ponts et Chaussées (LCPC)-Observatoire des Sciences de l'Univers de Grenoble [1985-2015] (OSUG [1985-2015]), and 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)

Subjects
landslides, rockfalls, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], fragmentation, power law distribution, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], natural hazard, self-organized criticality, [SDE.MCG.CPE]Environmental Sciences/Global Changes/domain_sde.mcg.cpe
Abstract

International audience; We analyze the volume distribution of natural rockfalls on different geological settings (i.e., calcareous cliffs in the French Alps, Grenoble area, and granite Yosemite cliffs, California Sierra) and different volume ranges (i.e., regional and worldwide catalogs). Contrary to previous studies that included several types of landslides, we restrict our analysis to rockfall sources which originated on subvertical cliffs. For the three data sets, we find that the rockfall volumes follow a power law distribution with a similar exponent value, within error bars. This power law distribution was also proposed for rockfall volumes that occurred along road cuts. All these results argue for a recurrent power law distribution of rockfall volumes on subvertical cliffs, for a large range of rockfall sizes (102–1010 m3), regardless of the geological settings and of the preexisting geometry of fracture patterns that are drastically different on the three studied areas. The power law distribution for rockfall volumes could emerge from two types of processes. First, the observed power law distribution of rockfall volumes is similar to the one reported for both fragmentation experiments and fragmentation models. This argues for the geometry of rock mass fragment sizes to possibly control the rockfall volumes. This way neither cascade nor avalanche processes would influence the rockfall volume distribution. Second, without any requirement of scale-invariant quenched heterogeneity patterns, the rock mass dynamics can arise from avalanche processes driven by fluctuations of the rock mass properties, e.g., cohesion or friction angle. This model may also explain the power law distribution reported for landslides involving unconsolidated materials. We find that the exponent values of rockfall volume on subvertical cliffs, 0.5 ± 0.2, is significantly smaller than the 1.2 ± 0.3 value reported for mixed landslide types. This change of exponents can be driven by the material strength, which controls the in situ topographic slope values, as simulated in numerical models of landslides [Densmore et al., 1998; Champel et al., 2002]. INDEX TERMS: 5104 Physical Properties of Rocks: Fracture and flow; 1815 Hydrology: Erosion and sedimentation; 8122 Tectonophysics: Dynamics, gravity and tectonics

Published
2003
Full Text
View/download PDF

49. Mainshocks are aftershocks of conditional foreshocks: how to foreshock statistical properties emerge from aftersock laws

Author

Helmstetter, Agnès, Sornette, D., Grasso, Jean-Robert, 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), Laboratoire de physique de la matière condensée (LPMC), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (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), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la Terre [2011-2015] (ISTerre [2011-2015]), 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)-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)-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), and COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], [SDE.MCG.CPE]Environmental Sciences/Global Changes/domain_sde.mcg.cpe
Abstract

International audience; The inverse Omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law ∝ 1/(tc − t)p ′ of the time to the mainshock occurring at tc. Here, we show that this law results from the direct Omori law for aftershocks describing the power law decay ∼ 1/(t − tc)p of seismicity after an earthquake, provided that any earthquake can trigger its suit of aftershocks. In this picture, the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding Omori law. The inverse Omori law then emerges as the expected (in a statistical sense) trajectory of seismicity, conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock. In particular, we predict and verify by numerical simulations on the Epidemic-Type-Aftershock Sequence (ETAS) model that p′ is always smaller than or equal to p and a function of p, of the b-value of the Gutenberg-Richter law (GR) and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock. The often documented apparent decrease of the b-value of the GR law at the approach to the main shock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock. However, we predict that the GR law is not modified simply by a change of b-value but that a more accurate statement is that the GR law gets an additive (or deviatoric) power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock. In the space domain, we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks towards the mainshock. In this model, foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock. Foreshocks are not just statistical creatures, they are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers.

Published
2003
Full Text
View/download PDF

50. Rupture et instabilités : sismicité et mouvements de terrain

Author

Helmstetter, Agnès, 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), Université Joseph-Fourier - Grenoble I, Grasso Jean-Robert(grasso@obs.ujf-grenoble.fr), Helmstetter, Agnes, 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 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), 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]), and 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)

Subjects
Aftershocks, Rupture, Instabilités graviaires, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Earthquakes, [SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Séismes, Répliques, Landslides
Abstract

We analyze the rupture associated with two natural phenomena, earthquakes and landslides. In the first part, we study a simple stochastic model of seismicity, based on the two best-established empirical laws for earthquakes, the power law decay of seismicity after an earthquake and the power law distribution of earthquake energies. This model assumes that each earthquake can trigger aftershocks, with a rate increasing with its magnitude. The seismicity rate is in this model the result of the whole cascade of direct and secondary aftershocks. We analyze the space-time organization of the seismic activity in the different sub- and super-critical regimes of the model. We show that this simple model can reproduce many properties of real seismicity, such as the variability of the aftershocks decay law, the acceleration of the seismic activity before large earthquakes, the diffusion of aftershocks, the migration of foreshocks, and the modification of the magnitude distribution before large earthquakes. We find that this model provides a good predictability for a fraction of earthquakes that are triggered by a previous large event. We demonstrate the essential role played by the cascades of earthquake triggering at all scales in controlling the seismic activity. The second part is devoted to the analysis of landslides. A study of several catalogs of rock falls shows that the distribution of rockfall volumes follows a power-law distribution, arising either from the scale invariant heterogeneity of the rock-mass, or from the dynamics of a self-organized critical system. We propose that the precursory acceleration of the displacement before some catastrophic landslides can be reproduced using a slider block model with a rate-and-state dependent friction law. Application of this model to two landslide slip histories suggests that we can distinguish an acceleration of the sliding velocity in the stable regime from an unstable acceleration leading to a catastrophic collapse., On s'intéresse à la rupture associée à deux classes de phénomènes naturels, les séismes et les instabilités gravitaires. Pour les séismes, on étudie un modèle stochastique de sismicité, basé sur les deux lois les mieux établies pour la sismicité, la décroissance en loi de puissance du taux de sismicité après un séisme, et la distribution en loi de puissance des énergies des séismes. Dans ce modèle, on suppose que chaque séisme déclenche d'autres séismes, dont le nombre augmente avec l'énergie du choc principal. Le taux de sismicité global résulte de la cascade de déclenchements de séismes directs et indirects. On analyse l'organisation spatiale et temporelle de la sismicité dans les différents régimes sous- et sur-critiques du modèle. Ce modèle permet de reproduire un grand nombre de propriétés de l'activité sismique, telles que la variabilité de la décroissance des séquences d'aftershocks, l'augmentation de l'activité sismique avant un séisme, la diffusion des aftershocks, la migration des foreshocks et la modification de la distribution des magnitudes avant un séisme. On obtient avec ce modèle une bonne prédictabilité d'une fraction des séismes qui sont déclenchés à court terme après un grand séisme. Nos résultats démontrent le rôle essentiel des cascades de déclenchement de séismes a toutes les échelles dans l'organisation de l'activité sismique. Concernant l'étude des instabilités gravitaires, une étude statistique de plusieurs catalogues d'éboulements rocheux montre que la distribution des volumes de roches suit une loi de puissance. On propose que cette distribution en loi de puissance résulte soit de l'hétérogénéité initiale de la matrice rocheuse, soit de la dynamique d'un système critique auto-organisé. Certains glissements de terrains sont précédés par une accélération de la vitesse de glissement avant la rupture finale. On peut reproduire l'évolution temporelle du glissement a l'aide d'un modèle de bloc rigide avec une loi de friction dépendante de la vitesse de glissement et de l'état de contact entre le bloc et sa surface de glissement. L'analyse de deux glissements de terrains avec ce modèle permet de distinguer une accélération du glissement dans le régime stable, d'une accélération instable qui évolue vers une rupture catastrophique.

Published
2002

Catalog

Books, media, physical & digital resources
See catalog results