scholarly journals The November 11 2019 Le Teil, France M5 earthquake: a triggered event in nuclear country

2020 ◽  
Author(s):  
Jean-Paul Ampuero ◽  
Jérémy Billant ◽  
Florent Brenguier ◽  
Olivier Cavalié ◽  
Francoise Courboulex ◽  
...  
Keyword(s):  
Stress Drop ◽  
Power Plants ◽  
Shallow Depth ◽  
Fault System ◽  
Coseismic Slip ◽  
Surface Rupture ◽  
Radar Images ◽  
Optical Images ◽  
Reverse Faulting ◽  
Induced Stresses

<p>An earthquake of magnitude 5 (Mw 4.9) occurred near the town of Le Teil, France on November 11 2019, causing damage locally and concern due to its proximity to nuclear facilities. Despite its moderate magnitude, this earthquake offers unique opportunities to advance basic and applied research on earthquakes in general, including our understanding of the largest and most destructive earthquakes and induced seismicity. We present here an overview of the source characteristics of this event and, based on analysis of InSAR and seismological observations and optical images, we discuss its potential relation to human activity. We also discuss the emerging unique research opportunities.</p><p>The Le Teil earthquake occurred in a low seismicity region, a moderate hazard zone that has nevertheless experienced damaging earthquakes in the past. Its hypocentral depth is particularly shallow, less than 1.5 km. Radar images delineate the surface rupture and constrain well the coseismic slip distribution. The surface rupture corresponds to the previously mapped La Rouvière fault, an ancient normal fault reactivated as reverse-faulting by the Le Teil earthquake. Slip is predominantly confined in the top ~1 km and extends along ~4.5 km along-strike with two main slip asperities and stress drop of a few MPa. A large cement quarry sits on top of the deep edge of the rupture area, ~1 km above the fault. Based on optical images we estimate the distribution of mass extracted from the nearby quarry since 1947. We then compute the induced Coulomb stresses on the fault: they are favorable for reverse faulting and reach about 150 kPa, within the range of stresses that have been previously reported to trigger earthquakes, but substantially smaller than the coseismic stress drop. Analysis of the mainshock and quarry blast signals on the nearest stations (8.5 to 45 km distance) places the mainshock epicenter within the area of influence of the quarry-induced stresses. </p><p>These analyses so far indicate that the Le Teil event is likely a triggered earthquake: its initiation was favored by the quarry-induced stresses, but the bulk of its rupture propagation was enabled by naturally pre-existing stresses. We also report on directivity analyses based on various data subsets, which remain to be reconciled, possibly pointing to a non-trivial rupture path.</p><p>The characteristics of the Le Teil earthquake bear on important questions: how can earthquakes nucleate at such shallow depth? what confines slip at such shallow depth? do structural features control the patchy distribution of slip? how do elongated ruptures stop? It also offers a unique opportunity to study directly, by drilling at seismogenic depth, the three key spots of an earthquake: its hypocenter, its large slip area and its arrest area. The high aspect ratio of the rupture, comparable to that of the largest earthquakes, opens a window into the physics of very large earthquakes. Continued research would also address implications for seismic hazard in low-seismicity areas, including the safety of nearby nuclear power plants, especially by monitoring the unbroken sections of the fault system.</p>

scholarly journals Surface Rupture Kinematics and Coseismic Slip Distribution during the 2019 Mw7.1 Ridgecrest, California Earthquake Sequence Revealed by SAR and Optical Images

2020 ◽  
Vol 12 (23) ◽  
pp. 3883
Author(s):  
Chenglong Li ◽  
Guohong Zhang ◽  
Xinjian Shan ◽  
Dezheng Zhao ◽  
Yanchuan Li ◽  
...  
Keyword(s):  
Strike Slip ◽  
Earthquake Sequence ◽  
Slip Distribution ◽  
Fault System ◽  
Seismogenic Fault ◽  
Coseismic Slip ◽  
Surface Rupture ◽  
Lateral Strike Slip ◽  
Optical Images ◽  
Rupture Kinematics

The 2019 Ridgecrest, California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults. To characterize the surface rupture kinematics and fault slip distribution, we used optical images and Interferometric Synthetic Aperture Radar (InSAR) observations to reconstruct the displacement caused by the earthquake sequence. We further calculated curl and divergence from the north-south and east-west components, to effectively identify the surface rupture traces. The results show that the major seismogenic fault had a length of ~55 km and strike of 320° and consisted of five secondary faults. On the basis of the determined multiple-fault geometries, we inverted the coseismic slip distributions by InSAR measurements, which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip (maximum strike-slip of ~5.8 m at the depth of ~7.5 km), with a small dip-slip component (peaking at ~1.8 m) on an east-dipping fault. The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault. These earthquakes triggered obvious aseismic creep along the Garlock fault (117.3° W–117.5° W). These results are consistent with the rupture process of the earthquake sequence, which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults.

Insights on fault reactivation during the 2019, Mw4.9 Le Teil earthquake in southeastern France, from a joint 3D geology and InSAR study

2021 ◽  
Author(s):  
Léo Marconato ◽  
Philippe-Hervé Leloup ◽  
Cécile Lasserre ◽  
Séverine Caritg ◽  
Romain Jolivet ◽  
...  
Keyword(s):  
Time Series ◽  
Surface Displacement ◽  
Fault Reactivation ◽  
Least Square ◽  
Shallow Depth ◽  
Slip Distribution ◽  
Fault System ◽  
Geological Model ◽  
Coseismic Slip ◽  
3D Geological Model

<div> <div> <div> <p>The 2019, M<sub>w</sub>4.9 Le Teil earthquake occurred in southeastern France, causing important damage in a slow deforming region. Field based, remote sensing and seismological studies following the event revealed its very shallow depth, a rupture length of ~5 km with surface rupture evidences and a thrusting mechanism. We further investigate this earthquake by combining geological field mapping and 3D geology, InSAR time series analysis and coseismic slip inversion.</p> <p>From structural, stratigraphic and geological data collected around the epicenter, we first produce a 3D geological model over a 70 km<sup>2</sup> and 3 km deep zone surrounding the 2019 rupture, using the GeoModeller software. This model includes the geometry of the main faults and geological layers, and especially a geometry for La Rouvière Fault, an Oligocene normal fault likely reactivated during the earthquake.</p> <p>We also generate a time series of the surface displacement by InSAR, based on Sentinel-1 data ranging from early January 2019 to late January 2020, using the NSBAS processing chain. The spatio-temporal patterns of the surface displacement for this limited time span show neither clear pre-seismic signal nor significant postseismic slip. We extract from the InSAR time series the coseismic displacement pattern, and in particular the along-strike slip distribution that shows spatial variations. The maximum relative displacement along the Line-Of-Sight is up to ~16 cm and is located in the southwestern part of the rupture.</p> <p>We then invert for the slip distribution on the fault from the InSAR coseismic surface displacement field. We use a non-negative least square approach based on the CSI software and the fault surface trace defined in the 3D geological model, exploring the range of plausible fault dip values. Best-fitting dips range between 55° and 60°. Such values are slightly lower than those measured on La Rouvière Fault planes in the field. Our model confirms the reactivation of La Rouvière fault, with reverse slip at very shallow depth and two main slip patches reaching 30 cm and 24 cm of slip at 400-500m depth. We finally discuss how the 3D fault geometry and geological configuration could have impacted the slip distribution and propagation during the earthquake.</p> <p>This study is a step to better quantify strain accumulation and assess the seismic hazard associated with other similar faults along the Cévennes fault system, in a densely populated area hosting several nuclear plants.</p> </div> </div> </div>

Fault Rerupture during the July 2019 Ridgecrest Earthquake Pair from Joint Slip Inversion of InSAR, Optical Imagery, and GPS

2020 ◽  
Vol 110 (4) ◽  
pp. 1627-1643 ◽  
Author(s):  
Yohai Magen ◽  
Alon Ziv ◽  
Asaf Inbal ◽  
Gidon Baer ◽  
James Hollingsworth
Keyword(s):  
Stress Drop ◽  
Joint Inversion ◽  
Model Space ◽  
Causal Link ◽  
Fault System ◽  
Coseismic Slip ◽  
Aftershock Activity ◽  
Data Space ◽  
Rate Dependent ◽  
Optical Imagery

ABSTRACT The Ridgecrest earthquake pair ruptured a previously unknown orthogonal fault system in the eastern California shear zone. The stronger of the two, an Mw 7.1 earthquake that occurred on 6 July 2019, was preceded by an Mw 6.4 foreshock that occurred 34 hr earlier. In this study, distinct final slip distributions for the two earthquakes are obtained via joint inversion of Interferometric Synthetic Aperture Radar (InSAR), optical imagery, and Global Positioning System (GPS) measurements. Special attention is paid to the merging of dense (e.g., InSAR and optical imagery) and sparse geodetic (e.g., GPS) datasets. In addition, a new approach is introduced for data and model discretization through intermittent model- and data-space reconditioning that stabilizes the inversion, thus ensuring that small changes in the data space do not cause disproportionate large changes to the model space. Although the coseismic slip of the Mw 6.4 earthquake was complex, involving three distinct asperities distributed among an intersecting orthogonal set of faults, the coseismic slip of the Mw 7.1 earthquake was limited to the main northwest-striking fault. In addition to the Mw 7.1 earthquake, that northwest-striking fault plane also hosted one of the Mw 6.4 asperities. Slip on this coplanar foreshock asperity increased the shear stress at the future site of the Mw 7.1 hypocenter, and triggered a vigorous aftershock activity on the main northwest fault that culminated in its rupture. This, in turn, reactivated the coplanar foreshock asperity. In addition to failing twice within 34 hr, we find that the reruptured asperity slipped about six times more during the Mw 7.1 than during the Mw 6.4 earthquake. This repeated failure is indicative of an incomplete stress drop and premature rupture arrest during the Mw 6.4 foreshock, requiring an efficient frictional strengthening and emphasizing the causal link between highly rate-dependent friction, dynamic frictional restrengthening, and partial stress drop that has been observed in numerical studies of frictional sliding.

scholarly journals Assembly of a large earthquake from a complex fault system: Surface rupture kinematics of the 4 April 2010 El Mayor–Cucapah (Mexico) Mw 7.2 earthquake

Geosphere ◽  
2014 ◽  
Vol 10 (4) ◽  
pp. 797-827 ◽  
Author(s):  
John M. Fletcher ◽  
Orlando J. Teran ◽  
Thomas K. Rockwell ◽  
Michael E. Oskin ◽  
Kenneth W. Hudnut ◽  
...  
Keyword(s):  
Large Earthquake ◽  
Fault System ◽  
Surface Rupture ◽  
Complex Fault ◽  
Rupture Kinematics ◽  
Complex Fault System

scholarly journals Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 837-849 ◽  
Author(s):  
D. Díaz ◽  
A. Maksymowicz ◽  
G. Vargas ◽  
E. Vera ◽  
E. Contreras-Reyes ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Average Length ◽  
Sedimentary Cover ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Fault System ◽  
Surface Rupture ◽  
Thrust Tectonics ◽  
Rock Substratum ◽  
Fault Scarps

Abstract. The crustal-scale west-vergent San Ramón thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault surface rupture propagation, fault splays and fault segment transfer zones.

scholarly journals Fault geometry and earthquake mechanics

1994 ◽  
Vol 37 (6) ◽  
Author(s):  
D. J. Andrews
Keyword(s):  
Stress Concentration ◽  
Volume Change ◽  
Triple Junction ◽  
Stress Drop ◽  
Single Point ◽  
Stress Singularity ◽  
Confining Pressure ◽  
Fault System ◽  
Earthquake Mechanics ◽  
Fresh Fracture

Earthquake mechanics may be determined by the geometry of a fault system. Slip on a fractal branching fault surface can explain: 1) regeneration of stress irregularities in an earthquake; 2) the concentration of stress drop in an earthquake into asperities; 3) starting and stopping of earthquake slip at fault junctions, and 4) self-similar scaling of earthquakes. Slip at fault junctions provides a natural realization of barrier and asperity models without appealing to variations of fault strength. Fault systems are observed to have a branching fractal structure, and slip may occur at many fault junctions in an earthquake. Consider the mechanics of slip at one fault junction. In order to avoid a stress singularity of order 1/r, an intersection of faults must be a triple junction and the Burgers vectors on the three fault segments at the junction must sum to zero. In other words, to lowest order the deformation consists of rigid block displacement, which ensures that the local stress due to the dislocations is zero. The elastic dislocation solution, however, ignores the fact that the configuration of the blocks changes at the scale of the displacement. A volume change occurs at the junction; either a void opens or intense local deformation is required to avoid material overlap. The volume change is proportional to the product of the slip increment and the total slip since the formation of the junction. Energy absorbed at the junction, equal to confining pressure times the volume change, is not large enongh to prevent slip at a new junction. The ratio of energy absorbed at a new junction to elastic energy released in an earthquake is no larger than P/µ where P is confining pressure and µ is the shear modulus. At a depth of 10 km this dimensionless ratio has th value P/µ= 0.01. As slip accumulates at a fault junction in a number of earthquakes, the fault segments are displaced such that they no longer meet at a single point. For this reason the volume increment for a given slip increment becomes larger. A juction with past accumulated slip ??0 is a strong barrier to earthquakes with maximum slip um < 2 (P/µ) u0 = u0/50. As slip continues to occur elsewhere in the fault system, a stress concentration will grow at the old junction. A fresh fracture may occur in the stress concentration, establishing a new triple junction, and allowing continuity of slip in the fault system. The fresh fracture could provide the instability needed to explain earthquakes. Perhaps a small fraction (on the order of P/µ) of the surface that slips in any earthquake is fresh fracture. Stress drop occurs only on this small fraction of the rupture surface, the asperities. Strain change in the asperities is on the order of P/µ. Therefore this model predicts average strais change in an earthquake to be on the order of (P/µ)2 = 0.0001, as is observed.

scholarly journals Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence

2021 ◽  
Vol 58 ◽  
pp. 200
Author(s):  
Dimitrios Galanakis ◽  
Sotiris Sboras ◽  
Garyfalia Konstantopoulou ◽  
Markos Xenakis
Keyword(s):  
Normal Fault ◽  
Fault Scarp ◽  
Focal Mechanisms ◽  
Fault System ◽  
Spatiotemporal Evolution ◽  
Surface Rupture ◽  
Alluvial Deposits ◽  
Epicentral Area ◽  
Ground Shaking ◽  
Macroseismic Observations

On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.

scholarly journals In-Season Mapping of Irrigated Crops Using Landsat 8 and Sentinel-1 Time Series

2019 ◽  
Vol 11 (2) ◽  
pp. 118 ◽  
Author(s):  
Valérie Demarez ◽  
Florian Helen ◽  
Claire Marais-Sicre ◽  
Frédéric Baup
Keyword(s):  
Time Series ◽  
Shuttle Radar Topography Mission ◽  
Irrigation Scheduling ◽  
Landsat 8 ◽  
Radar Images ◽  
Optical Images ◽  
Multi Temporal ◽  
Irrigated Crops ◽  
Elevation Model ◽  
The Impact

Numerous studies have reported the use of multi-spectral and multi-temporal remote sensing images to map irrigated crops. Such maps are useful for water management. The recent availability of optical and radar image time series such as the Sentinel data offers new opportunities to map land cover with high spatial and temporal resolutions. Early identification of irrigated crops is of major importance for irrigation scheduling, but the cloud coverage might significantly reduce the number of available optical images, making crop identification difficult. SAR image time series such as those provided by Sentinel-1 offer the possibility of improving early crop mapping. This paper studies the impact of the Sentinel-1 images when used jointly with optical imagery (Landsat8) and a digital elevation model of the Shuttle Radar Topography Mission (SRTM). The study site is located in a temperate zone (southwest France) with irrigated maize crops. The classifier used is the Random Forest. The combined use of the different data (radar, optical, and SRTM) improves the early classifications of the irrigated crops (k = 0.89) compared to classifications obtained using each type of data separately (k = 0.84). The use of the DEM is significant for the early stages but becomes useless once crops have reached their full development. In conclusion, compared to a “full optical” approach, the “combined” method is more robust over time as radar images permit cloudy conditions to be overcome.

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