Pascal Bernard

Institut de Physique du Globe de Paris · Department of Seismology

The Mw 7.9 April 25, 2015 Gorkha earthquake is the latest of a millenary-long series of large devastating Himalayan earthquakes. It is also the first time a large Himalayan earthquake and its aftershocks were recorded by a local network of seismic stations. In the five years following the mainshock, more than 31 000 aftershocks were located by this...

Moderate‐to‐large earthquakes in rifts may occur on leading boundary faults or inner antithetic faults. Here we show a rare case of the 2020–2021 seismic sequence in the Corinth rift, that culminated in the shallow rupture of the antithetic fault, neither preceded nor followed by the leading fault rupture. The hypocenter of the largest shock (Mw 5....

The Near Fault Observatories (NFOs) community is one of the European Plate Observing System (EPOS, http://www.epos-eu.org) Thematic Communities, today consisting of six research infrastructures that operate in regions characterised by high seismic hazard originating from different tectonic regimes. Earthquakes respond to complex natural systems who...

In many areas with high telluric hazard, our understanding of the seismogenic and mechanical processes is limited by the difficulty or impossibility to deploy arrays of high-performance seismometers or of other geophysical sensors, due to high cost (e.g., offshore) and/or hazard (e.g., lightning, active volcano, high T in boreholes...) of the maint...

We present here the design, performance and in situ demonstration of an innovative, high resolution, low-cost optical (laser) seismometer. After a brief outline of the context and purposes, we present the optoelectronic interrogator designed and built by the ESEO team, its developments and performance. We also present the evolution of the associate...

The retrieval of earthquake finite-fault kinematic parameters after the occurrence of an earthquake is a crucial task in observational seismology. Routinely-used source inversion techniques are challenged by limited data coverage and computational effort, and are subject to a variety of assumptions and constraints that restrict the range of possibl...

The M=8.1, April 1st, 2014 Iquique earthquake, which broke part of the northern Chile seismic gap, was preceded by a strong foreshock sequence starting early January 2014. The reported analysis of the continuous records of the nearby GPS stations from the IPOC North Chili array lead to contradictory results concerning the existence and location of...

Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. Since 10 May 2018, magmatic activity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displac...

In the past 20 years, the Corinth Rift Laboratory (CRL) network has been closely monitoring the Western Gulf of Corinth (WGoC), the area being the main focus of the Corinth Rift Near Fault Observatory. The local seismological and geodetic network permitted the detection and location of microseismicity in high resolution, revealing complex sequences...

In post-mining regions with seismic hazard, timely decision making for risk management faces the challenge of quick and reliable detection and location of seismic events. As a response to the increasing density of monitoring stations, generating large volumes of seismic data, automatic, full waveform-based methods have been developed in recent year...

The retrieval of earthquake finite-fault kinematic parameters after the occurrence of an earthquake is a crucial task in observational seismology. Routinely-used source inversion techniques are challenged by limited data coverage and computational effort, and are subject to a variety of assumptions and constraints that restrict the range of possibl...

We investigate a seismic crisis that occurred in the western Gulf of Corinth (Greece) between December 2020 and February 2021. This area is the main focus of the Corinth Rift Laboratory (CRL) network, and has been closely monitored with local seismological and geodetic networks for 20 yr. The 2020–2021 seismic crisis evolved in three stages: It sta...

The problems of earthquake damage prevention and the effective seismic risk mitigation are critical issues that attract the interest of the seismological community and stakeholders globally. In particular, Rapid Seismic Risk Assessment (RSRA) methods gain increasing popularity and constitute the present state of the art regarding the earthquake thr...

The issues concerning the relationship between two self-similarity parameters-the Gutenberg-Richter band Omori p-values-in the aftershock sequences are explored. In the laboratory experiments, under fracture initiation in the rock by sharp jumps in the axial stress, a correlation between the p-and b-values is revealed in the fracture relaxation reg...

Accurate monitoring of volcanic activity demands expertise in fields including geophysics, geology, and geochemistry. Data obtained from the most recent technical advances are particularly vital in pre-eruptive phases. In particular, seismic monitoring in near real time is essential to locating and discriminating early signs among different sources...

The 2014 Iquique seismic crisis in Chile, culminating with a Mw 8.1 earthquake on 1 April, highlights a complex unlocking of the Northern Chilean subduction that has been considered a seismic gap since 1877. During the year preceding this event, at least three clusters of seismic activity have been reported: in July 2013 and January and March 2014....

In this work we investigated seismic and aseismic rock mass behaviors in response to deep underground mining. For this purpose, an area under production of the metal mine of Garpenberg (Sweden) was instrumented with a geophysical and geotechnical monitoring network. In situ monitoring data were analyzed and interpreted considering mining operations...

and, direction des risques du sol et du sous-sol, unite áuscultation et surveillance geotechnique et geophysique Abstract 12 Seismic repeaters are a phenomenon rarely observed in mining environments. In this study, 13 we show that repeaters and associated aseismic slip can be the governing mechanism behind 14 seismic triggering in response to excav...

Recent studies have demonstrated the success of automatic full-waveform detection and location methods in analyzing and monitoring natural and induced seismicity. These approaches have been shown to provide a significant improvement in events detectability, increasing the significance of statistical analysis that permits to identify small changes o...

We report here the design, performance, and in situ demonstration, on‐land and offshore, of an innovative high‐resolution low‐cost optical (laser) seismometer. The instrument was developed within the Laser Interferometry for Earth Strain project (French Agence Nationale de la Recherche [ANR] program), and first tested at the low‐noise underground l...

With the aim of better understanding the mechanical behavior of rocks solicited by underground excavations, the rock mass response to mining was studied based on a comprehensive approach. For this purpose, a deep area of the metal mine of Garpenberg (Sweden) was instrumented with a geophysical and geotechnical monitoring network. In situ monitoring...

Plain Language Summary In most models and analyses, small earthquakes (i.e., magnitude less than 4) are considered either point sources or homogeneous “penny‐shaped” surfaces. While these assumptions may be valid, details of earthquake ruptures are more complex. Here we study a magnitude 3 induced earthquake that occurred in the St. Gallen geotherm...

A recent work by Kimura et al. (Earth Planets Space 71:27, 2019. https://doi.org/10.1186/s40623-019-1006-x) (hereafter referred to as K19) claims to provide the first observational constraints on the prompt elastogravity signals (PEGS) induced by an earthquake. To make their claim, the authors argue that the observations shown in Vallée et al. (Sci...

High-frequency (HF) seismic radiation is associated with abrupt changes of rupture velocity and slip-rate during earthquake faulting. Many studies have attempted to illuminate rupture heterogeneities of large earthquakes through the use of coherent imaging techniques such as the back-projection (BP) [e.g. Satriano et al. (2014), Lay et al. (2012)]....

Multiple studies have demonstrated the efficiency of automatic full waveform-based detection and localization approaches. Application of these techniques has shown significant improvement in detection capacity compared to the triggered-based system. The increased number of detected events allows to perform detailed statistical analysis of seismicit...

In many areas with high telluric hazard (earthquakes, tsunamis, landslides etc.), our understanding of seismogenic and mechanical processes and our ability to properly asses the related hazard is still very limited by the difficulty or the impossibility to deploy arrays of high performance seismometers in areas with harsh and challenging environmen...

A recent work by Kimura et al. (2019) (hereafter referred to as K19) claims to provide the first observational constraints on the prompt elastogravity signals (PEGS) induced by an earthquake. To make their claim, the authors argue that the observations shown in Vallée et al. (2017) (hereafter referred to as V17) are spurious and their modeling inac...

Laboratory experiments on studying the aftershock regime are carried out with sandstone specimens under different axial loading and uniform compression and constant pore pressure. The aftershock sequences are modeled by the scenario of stepwise increasing axial loading of a specimen with strain control ensuring regular generation of aftershock sequ...

In the Lorraine area of eastern France, decades of iron-ore mining from 1850 to 1997 have left vast underground cavities beneath or in the vicinity of urban areas. Several major collapses occurred in the southern part of this iron-ore basin in the 1990s, after the mine closure and the flooding of underground mine workings. Following these large-sca...

With the aim of understanding the nature of mining-induced seismicity, microseismic activity in the deep metal mine of Garpenberg (Sweden) has been recorded during 2 years of excavations. The studied area of the mine is operated using sublevel stoping method with backfilling, between depths of around 1000 and 1300 meters. Spatiotemporal analysis of...

Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens at different levels of axial loading and uniform compression and at constant pore pressure. The aftershock sequences are modeled by the scenario of stepwise increasing axial loading of a specimen with strain control, which ensures the regular generation...

À la suite du séisme de l’Aquila, en Italie, en 2009, des sismologues italiens ont été condamnés en première instance à une peine de prison ferme, accusés de n’avoir pas su prévoir les événements. Les géophysiciens français travaillant sur les risques telluriques se sont alors interrogés sur le degré de préparation de la communauté scientifique fra...

Volcanic eruptions are foundational events shaping the Earth's surface and providing a window into deep Earth processes and composition. Most eruptions occur on established volcanoes, exploiting longstanding magma reservoirs and pathways. Those creating new volcanoes are rare and usually too small or too remote to be well monitored, particularly in...

The objective of this work is to interpret the relation between the heterogeneities of the rupture process and the high-frequency (HF) seismic radiation by using the back-projection (BP) imaging technique. Understanding the nature of HF emissions becomes crucial not only in the study of earthquake rupture mechanism, by revealing its complexity, but...

Recent studies reported the observation of prompt elastogravity signals during the 2011 M9.1 Tohoku earthquake, recorded with broadband seismometers and gravimeter between the rupture onset and the arrival of the seismic waves. Here we show that to extend the range of magnitudes over which the gravity perturbations can be observed and reduce the ti...

As soon as an earthquake starts, the rupture and the propagation of seismic waves redistribute masses within the Earth. This mass redistribution generates in turn a long-range perturbation of the Earth gravitational field, which can be recorded before the arrival of the direct seismic waves. The recent first observations of such early signals motiv...

We analyze the complete earthquake archive of the western Corinth Rift using both cross-correlations between pairs of event waveforms and accurate differential travel times observed at common stations, in order to identify small-scale fault structures at depth. The waveform database was generated by the dense Corinth Rift Laboratory network and inc...

In this study, we demonstrate the capability of an automatic network-based detection and location method to extract and analyse different components of tectonic tremor activity by analysing a 9-day energetic tectonic tremor sequence occurring at the down-dip extension of the subducting slab insouthwestern Japan. The applied method exploits the cohe...

Gravity gets into the earthquake game Earthquakes generate large movements of mass, which slightly change the gravitational field. Unlike the elastic waves that propagate from the earthquake, the gravity perturbations travel at the speed of light. Vallée et al. have finally observed these gravity perturbations in seismometer records from the great...

This work presents a numerical approach for evaluating the performances of microseismic networks (EMAP) in terms of detection and location capabilities and of location errors distribution. Knowing the seismic network geometry, the noise level at each seismic station, the attenuation law and the velocity model in the crossed medium, EMAP determines...

The Valparaiso 2017 sequence occurred in the Central Chile mega-thrust, an active zone where the last mega-earthquake occurred in 1730. Intense seismicity started 2 days before the Mw 6.9 main-shock, a slow trench-ward movement was observed in the coastal GPS antennas and was accompanied by foreshocks and repeater-type seismicity. To characterize t...

The study reports an unusual water level rise in the Gulf of Corinth, central Greece, during the passing of the seismic waves of the remote 2011 9.0 Tohoku earthquake. The seismic seiches were recorded by a tide-gauge located in the marina of the island of Trizonia, in the western side of the gulf. The cross-analysis between the ground motion and t...

Three years of continuous waveform data recorded at 22 stations from the Corinth Rift Laboratory and the Hellenic Unified Seismological Network are used to perform an ambient noise surface-wave tomography of the western Corinth Rift. All available vertical component time-series were cross-correlated to extract empirical Rayleigh-wave Green's functi...

Near Fault Observatories (NFOs) are innovative research infrastructures based on dense, state of the art networks of multi-parametric sensors that continuously monitor the underlying Earth instability processes over a broad time interval. They aim at understanding the physical/chemical processes responsible for earthquakes and faulting and tracking...

We first focus on slow transient forcings occuring in the western Corinth Rift, with evidence of (1) fluid pore pressure migrations during the large 2003-2004 swarm, (2) creep through a repeater-like multiplet initiating the 2003-2004 seismic crisis. Persistent multiplets with activity spanning several years suggest some forcing by creep and are lo...

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture,...

The Corinth rift (Greece) is one of the most active tectonic structures of the euro-mediterranean area. Its north- south opening rate of around 1.5 cm.yr−1 results into a high microseismicity level and a few destructive M>6 earthquakes per century. The seismic activity follows a swarm organization with alternation of intensive crisis and more quies...

We present a new methodology for detection and space-time location of seismic sources based on multiscale, frequency-selective coherence of the wave field recorded by dense large-scale seismic networks and local antennas.The method is designed to enhance coherence of the signal statistical features across the array of sensors and consists of three...

http://gji.oxfordjournals.org/content/early/2016/04/29/gji.ggw163.abstract?keytype=ref&ijkey=TXW3ako2zyzGp6N

The Corinth Rift separates Peloponnesus to the south from mainland Greece to the north. It is one of the most active extensional intra-continental rifts in the world, with geodetically measured rates of extension varying from ∼5 mm/yr at the eastern part to ∼15 mm/yr at the western part. This work presents a first attempt to study the crustal veloc...

The Corinth rift (Greece) is made of a complex network of fault segments, typically 10–20 km long separated by stepovers. Assessing the maximum magnitude possible in this region requires accounting for multisegment rupture. Here we apply numerical models of dynamic rupture to quantify the probability of a multisegment rupture in the rift, based on...

The 2014 Iquique seismic crisis, culminating with the main Mw 8.2 Iquique earthquake (Chile), 1st of April 2014, and the largest Mw 7.7 aftershock, 3rd of April, highlighted a complex unlocking of the North Chile subduction interface. Indeed, during many months preceding this event, at least three large seismic clusters have been observed, in July...

We develop a mechanical model of tight clusters of coplanar seismic asperities, to investigate a particular microearthquake swarm located at 8 km depth in the Corinth rift in Greece, which was active between 2001 and 2007. Although it is classified as a multiplet based on waveform similarity, this seismic sequence is much more complex than a repeat...

The Corinth Rift in Central Greece has been studied extensively during the past decades, as it is one of the most seismically active regions in Europe. It is characterized by normal faulting and extension rates between 6 and 15 mm yr-1 in an approximately N10E° direction. On 2013 May 21, an earthquake swarm was initiated with a series of small even...

We propose a method to precisely estimate earthquake source parameters as magnitude, size of rupture, stress-drop and coseismic slip, and their uncertainties. This method, that relies on a Bayesian approach, allows the determination of the scalar seismic moment, corner frequency (fc) and their associated uncertainties, by inverting ratios between s...

Sensitive instruments like strainmeters and tiltmeters are are necessary for measuring slowly-varying low amplitude earth deformations. Nonetheless, laser and fiber interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy. In this paper, a practical design of a simple pendulum borehole...

Microseismic multiplets occurring in the western Corinth rift, Greece, during a large swarm are analyzed to retrieve their spatio-temporal characteristics. These multiplets activated small subfaults at depth (~7 km), up to 1 km long, at the root oftwo parallel active normal faults. The swarm migrates westward nearly horizontally over 10 km at an av...

The results of the laboratory experiment on the initiation of acoustic emission in a loaded specimen by wetting a part of its surface without a material increase in the pore pressure are analyzed. The experiment was conducted on the lever press at the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences (Sobolev and Ponomarev, 201...

Ground failures, caving processes and collapses of large natural or man-made underground cavities can produce significant socio-economic damages and represent a serious risk envisaged by the mine managements and municipalities. In order to improve our understanding of the mechanisms governing such a geohazard and to test the potential of geophysica...

11 , Efthimios SOKOS 12 , Kostas MAKROPOULOS 13 The Corinth Rift in Central Greece has been studied extensively during the past decades, as it is one of the most seismically active regions in Europe. It is characterized by normal faulting in an approximate WSW-ENE direction with an extension rate increasing from east (~6 mm/yr) to west (~14 mm/yr)...

The issue of earthquake source scaling continues to draw considerable debate within the seismological community: observation supporting and refuting that systematic differences between the source processes of small and large earthquakes are still discussed. This motivates the study of how source parameters, such as seismic moment and corner frequen...

High-resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow-slip events, and to estimate slow transients related to earthquake swarms. However, they are also sensitive to other numerous influences, internal or external. Furthermore, the quality of their coupling to the rock through cementation,...

We study 24 multiplets of the 2003-2004 seismic crisis, located in the south-western part of the Corinth Rift about 7km depth, in terms of spatio-temporal characteristics (size, geometry and diffusivity). Results show a compatibility of the migration velocity of microseismic activity with the propagation velocities of a fluid surpressure. Diffusivi...

The 2008 M-w = 6.4 Movri earthquake ruptured a NNE right lateral strike-slip fault about 30 km south of the city of Patras. Although some strike-slip activity on minor faults was known, there was no tectonic evidence of large scale NS striking fault and such a large event was not anticipated. Following the event, a network of six stations was insta...

The Corinth rift is one of the most seismically zones in Europe. The seismic activity is characterized by numerous multiplets. A multiplet is a group of earthquakes with similar waveforms resulting from close location and focal mechanism. Multiplets are often associated with small asperities and can be seen as repeated ruptures due to transient for...

The seismic activity in the western part of the Corinth Rift (Greece) over the period 2000-2007, monitored by a dense network of three-component stations, is analysed in terms of multiplets and high precision relocation using double difference techniques. This detailed analysis provides new insights into the geometry of faults at depth, the nature...

The composite fault plane solutions for 24 large multiplets recorded in the western part of the Corinth Rift between 2000 and 2007 are computed by jointly inverting P polarities and Sv/P, Sh/P, Sv/Sh amplitude ratios of the direct waves. The fault plane solutions are determined using 1-D and 3-D velocity models. Solutions computed with the 3-D velo...

The data of the known field experiment on water injection in the borehole were analyzed. Parameters of self-similarity of seismicity were estimated in comparison with the changes of water pressure. Changes of seismicity parameters that indicate the redistribution of the failure from lower scales to upper are revealed. The total number of earthquake...