GPR measurements to assess the Emeelt active fault's characteristics in a highly smooth topographic context, Mongolia

International audienceTo estimate the seismic hazard, the geometry (dip, length and orientation) and the dynamics (type of displacements and amplitude) of the faults in the area of interest need to be understood. In this paper, in addition to geomorphologic observations, we present the results of two ground penetrating radar (GPR) campaigns conducted in 2010 and 2011 along the Emeelt fault in the vicinity of Ulaanbaatar, capital of Mongolia, located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes. As the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event, the fault location and geometry is difficult to determine precisely. However, by using GPR first, a non-destructive and fast investigation, the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location. GPR was performed with a 50 MHz antenna over 2-D lines and with a 500 MHz antenna for pseudo-3-D surveys. The 500 MHz GPR profiles show a good consistency with the trench observations, dug next to the pseudo-3-D surveys. The 3-D 500 MHz GPR imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m. This is consistent with a right lateral strike-slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6. The 2-D 50 MHz profiles, recorded perpendicular to the fault, show a strong reflection dipping to the NE, which corresponds to the fault plane. Those profiles provided complementary information on the fault such as its location at shallow depth, its dip angle (from 23 • to 35 •) and define its lateral extension. Central Asia is known for its high level of seismic hazards, especially Mongolia, which has been one of the most seismically active intracontinental regions in the world with four large earthquakes (magnitude around 8) along its active faults in the western part of the country during the last century (Khilko et al. 1985). The deformation in Mongolia is located between compressive structures related to the collision and penetration of the Indian plate into the Eurasian plate and extensive structures in the north of the country related with the Baykal rift (Tapponnier & Molnar 1979; Baljinnyam et al. 1993; Schlupp 1996; Bayasgalan & Jackson 1999). The seismic activity observed in the vicinity of Ulaanbaatar (UB), capital of Mongolia, is relatively low compared to the activity observed in western Mongolia. Nevertheless, since 2005, the seismic activity around UB not only has increased, but is also organized (see Fig. 1) at the west of UB along two perpendicular directions, which determine two active faults: Emeelt fault, discovered in 2008 (NNW-SSE direction, 25-km-long minimum and situated about 10 km W of UB) and Hustai fault (WSW–ENE direction, 80 km long, with its NE tip at less than 20 km west of UB); their length and morphology indicate that they can produce earthquakes of magnitude 6.5–7.5 (Schlupp et al. 2012). Most of the Mongolian population (1.2 million over 3 million) is concentrated at UB, which is the main political and economical centre of the country. Hence, the study of seismic hazard and the estimation of the probability of future destructive earthquakes are of primary importance for the country (Dugarmaa et al. 2006). Since the last large earthquake, the faults geomorphology has been highly smoothed by erosional processes and the exact location of the fault plane surface rupture is thus hidden within a several metre wide strip. The GPR method has been proven to give good and useful results to characterize faults by identifying offsets of radar reflections (Malik et al. 2007; Christie et al. 2009; Yalçiner et al. 2013) an

A Probabilistic Approach to Seismic Hazard in Metropolitan France

In this study, we applied a probabilistic methodology to seismic hazard assessment in metropolitan France. For that purpose we determined an attenuation law adapted to the French context. This law holds for peak ground acceleration on stiff bedrock for earthquakes with local magnitudes between 2.5 and 5.6 recorded in near field (at distances between 3 and 50 km). Geological conditions are taken into account by means of a three-categories classification of lithologies based on a 1/1,000,000 geological map. The seismotectonic zonation consists of areas of diffuse seismicity characterized by a frequency-magnitude distribution. In southeastern France, active faults are considered in a test case and are assumed to follow the characteristic earthquake model. We performed hazard curves for six French cities and maps of peak horizontal ground accelerations expected for return periods of 475, 975, and 1975 years in the country. Sensitivity tests have been performed. The uncertainty introduced by ground-motion variability seems minor compared with that due to the choice of the attenuation law. This study points to the importance of testing internal consistency of the various data and laws used in any seismic hazard analysis (in particular, here the type of magnitude used to predict ground motion). If not, some systematic bias is introduced that may result in systematic errors on peak ground acceleration determination. We also show that the introduction of possibly very large and infrequent events, known only from paleoseismic investigations, may have a dramatic impact on the hazard, especially when long periods of time are considered

Molecular evolution of the human SRPX2 gene that causes brain disorders of the Rolandic and Sylvian speech areas

<p>Abstract</p> <p>Background</p> <p>The X-linked <it>SRPX2 </it>gene encodes a Sushi Repeat-containing Protein of unknown function and is mutated in two disorders of the Rolandic/Sylvian speech areas. Since it is linked to defects in the functioning and the development of brain areas for speech production, <it>SRPX2 </it>may thus have participated in the adaptive organization of such brain regions. To address this issue, we have examined the recent molecular evolution of the <it>SRPX2 </it>gene.</p> <p>Results</p> <p>The complete coding region was sequenced in 24 human X chromosomes from worldwide populations and in six representative nonhuman primate species. One single, fixed amino acid change (R75K) has been specifically incorporated in human SRPX2 since the human-chimpanzee split. The R75K substitution occurred in the first sushi domain of SRPX2, only three amino acid residues away from a previously reported disease-causing mutation (Y72S). Three-dimensional structural modeling of the first sushi domain revealed that Y72 and K75 are both situated in the hypervariable loop that is usually implicated in protein-protein interactions. The side-chain of residue 75 is exposed, and is located within an unusual and SRPX-specific protruding extension to the hypervariable loop. The analysis of non-synonymous/synonymous substitution rate (Ka/Ks) ratio in primates was performed in order to test for positive selection during recent evolution. Using the branch models, the Ka/Ks ratio for the human branch was significantly different (p = 0.027) from that of the other branches. In contrast, the branch-site tests did not reach significance. Genetic analysis was also performed by sequencing 9,908 kilobases (kb) of intronic <it>SRPX2 </it>sequences. Despite low nucleotide diversity, neither the HKA (Hudson-Kreitman-Aguadé) test nor the Tajima's D test reached significance.</p> <p>Conclusion</p> <p>The R75K human-specific variation occurred in an important functional loop of the first sushi domain of SRPX2, indicating that this evolutionary mutation may have functional importance; however, positive selection for R75K could not be demonstrated. Nevertheless, our data contribute to the first understanding of molecular evolution of the human <it>SPRX2 </it>gene. Further experiments are now required in order to evaluate the possible consequences of R75K on SRPX2 interactions and functioning.</p

Rapid response to the M_w 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics

Néotectoniques de la Mongolie occidentale analysée à partir de données de terrain, sismologiques et satellitaires

Unrapport de thèse + une carte AOMongolia characterize the transition between compressive structures associated with India-Asia collision and extensive structures from Baykal rift. It suffered, since 1905, four earthquakes with magnitude larger then 8, (Tsetserleg, Bolnay, Fu Yun and Gobi-Altay). Ruptures associated with those earthquakes draw up a parallelogram composed by senestral strike slip faults on an east-west direction and dextral strike slip faults on NNW-SSE direction. Inside this parallelogram, the Hangay dome is associated with normal faults and recent alkaline volcanism. The source history of these two 1905 earthquakes shows a predominating propagation of the rupture to the east. The Tsetserleg earthquake ruptures (Mw = 7,95 ± 0,02.) may continue beyond the mapped ruptures. The nucleation of Bolnay earthquake (Mw = 8,4 ± 0,1) took place at the intersection between the main fault and the Teregtiin fault. Ruptures associated with the Gobi-Altay earthquake are complexes and run along the Ikhe Bogdo massif which rotate counterclockwise (24° ± 11° ) since the Miocene. Time recurrence on this fault is around 5000 years with a rate of around 1 mm/year. The displacement on the Altay and Gobi-Altay conjugates strike slip faults is absorbed on reverse faults, the whole creating compressive wedge. The Hangay dome results from the combination between a mantel up welling and the compressive front associated with India-Asia collision. The Hangay dome rotate clockwise. The sismicity characterize late aftershocks associated with recent earthquakes. These aftershocks are numerous on segments with vertical slip and few on strike slip segments. A compression oriented N20 ± 10° can explain all deformations indicating the actual preponderance of the compressive front associated to India-Asia collision, preceded by a mantel episode which prepared the region. We propose a model of pure deformation combined with a clockwise rotation in Mongolia.La Mongolie caractérise la transition entre les structures compressives liées à la collision Inde-Asie et extensives du rift du Baïkal. Elle a connu depuis 1905 quatre séismes de magnitude supérieure ou égale à 8, (Tsetserleg, Bolnaï, Fu Yun et Gobi-Altaï). Les ruptures associées à ces événements forment un parallélogramme composé par des failles décrochantes sénestres est-ouest et décrochantes dextres NNO-SSE. Au centre, le dôme du Hangaï est associé à des failles normales et à un volcanisme alcalin récent. L'étude de la source des deux séismes de 1905 indique une propagation dominante des ruptures vers l'est. Le séisme de Tsetserleg (Mw = 7,95 ± 0,02.) aurait continué au-delà des ruptures cartographiées. L'initiation du séisme de Bolnaï (Mw = 8,4 ± 0,1) s'est faite à l'intersection entre la faille principale et celle de Teregtiin. Les ruptures associées au séisme du Gobi-Altaï sont complexes et bordent le massif de Ikhe Bogdo qui subit une rotation antihoraire (24° ± 11° ) depuis le Miocène. L'intervalle de récurrence sur cette faille est d'environ 5000 ans avec une vitesse d'environ 1 mm/an. Le mouvement sur les failles décrochantes conjuguées de l'Altaï et du Gobi-Altaï est amorti sur des failles inverses, l'ensemble formant des coins en compression. La formation du dôme du Hangaï est le résultat d'une combinaison entre un panache mantélique et du front compressif lié à la collision Inde-Asie. Le massif subit une rotation horaire. La sismicité correspond à des répliques tardives des séismes récents plus nombreuses sur les segments à rejet vertical que décrochants. Une compression orientée N20 ± 10° permet d'expliquer toutes les déformations indiquant la prépondérance actuelle du front compressif associé à la collision Inde-Asie, précédée d'un épisode mantélique qui a préparé la région. Nous proposons un modèle de déformation pure combinée avec une rotation horaire pour la Mongolie

NEOTECTONIQUE DE LA MONGOLIE OCCIDENTALE ANALYSEE A PARTIR DE DONNEES DE TERRAIN, SISMOLOGIQUES ET SATELLITAIRES

Unrapport de thèse + une carte AOMongolia characterize the transition between compressive structures associated with India-Asia collision and extensive structures from Baykal rift. It suffered, since 1905, four earthquakes with magnitude larger then 8, (Tsetserleg, Bolnay, Fu Yun and Gobi-Altay). Ruptures associated with those earthquakes draw up a parallelogram composed by senestral strike slip faults on an east-west direction and dextral strike slip faults on NNW-SSE direction. Inside this parallelogram, the Hangay dome is associated with normal faults and recent alkaline volcanism. The source history of these two 1905 earthquakes shows a predominating propagation of the rupture to the east. The Tsetserleg earthquake ruptures (Mw = 7,95 ± 0,02.) may continue beyond the mapped ruptures. The nucleation of Bolnay earthquake (Mw = 8,4 ± 0,1) took place at the intersection between the main fault and the Teregtiin fault. Ruptures associated with the Gobi-Altay earthquake are complexes and run along the Ikhe Bogdo massif which rotate counterclockwise (24° ± 11° ) since the Miocene. Time recurrence on this fault is around 5000 years with a rate of around 1 mm/year. The displacement on the Altay and Gobi-Altay conjugates strike slip faults is absorbed on reverse faults, the whole creating compressive wedge. The Hangay dome results from the combination between a mantel up welling and the compressive front associated with India-Asia collision. The Hangay dome rotate clockwise. The sismicity characterize late aftershocks associated with recent earthquakes. These aftershocks are numerous on segments with vertical slip and few on strike slip segments. A compression oriented N20 ± 10° can explain all deformations indicating the actual preponderance of the compressive front associated to India-Asia collision, preceded by a mantel episode which prepared the region. We propose a model of pure deformation combined with a clockwise rotation in Mongolia.La Mongolie caractérise la transition entre les structures compressives liées à la collision Inde-Asie et extensives du rift du Baïkal. Elle a connu depuis 1905 quatre séismes de magnitude supérieure ou égale à 8, (Tsetserleg, Bolnaï, Fu Yun et Gobi-Altaï). Les ruptures associées à ces événements forment un parallélogramme composé par des failles décrochantes sénestres est-ouest et décrochantes dextres NNO-SSE. Au centre, le dôme du Hangaï est associé à des failles normales et à un volcanisme alcalin récent. L'étude de la source des deux séismes de 1905 indique une propagation dominante des ruptures vers l'est. Le séisme de Tsetserleg (Mw = 7,95 ± 0,02.) aurait continué au-delà des ruptures cartographiées. L'initiation du séisme de Bolnaï (Mw = 8,4 ± 0,1) s'est faite à l'intersection entre la faille principale et celle de Teregtiin. Les ruptures associées au séisme du Gobi-Altaï sont complexes et bordent le massif de Ikhe Bogdo qui subit une rotation antihoraire (24° ± 11° ) depuis le Miocène. L'intervalle de récurrence sur cette faille est d'environ 5000 ans avec une vitesse d'environ 1 mm/an. Le mouvement sur les failles décrochantes conjuguées de l'Altaï et du Gobi-Altaï est amorti sur des failles inverses, l'ensemble formant des coins en compression. La formation du dôme du Hangaï est le résultat d'une combinaison entre un panache mantélique et du front compressif lié à la collision Inde-Asie. Le massif subit une rotation horaire. La sismicité correspond à des répliques tardives des séismes récents plus nombreuses sur les segments à rejet vertical que décrochants. Une compression orientée N20 ± 10° permet d'expliquer toutes les déformations indiquant la prépondérance actuelle du front compressif associé à la collision Inde-Asie, précédée d'un épisode mantélique qui a préparé la région. Nous proposons un modèle de déformation pure combinée avec une rotation horaire pour la Mongolie

Séisme à la Martinique. 29 novembre 2007. La Trinité. Dégâts à l'école Auguste Réjon

Damage to the right of the connection of the staircase of the Auguste Réjon school in the commune of La Trinité following the earthquake of November 29, 2007 in Martinique.The Auguste Réjon School (Bonséjour district) dates from the 1960s, it is a RC+2 building with no crawl space and no basement. It has expansion joints and has a reinforced concrete column-beam structure with masonry fillings. It is composed of two buildings, forming an "L", connected to each other by a staircase and has balconies for each floor along its entire length.The building suffered from the earthquake only very locally, at the level of the staircase connecting the two buildings. It is supported by the main building. The exterior wall of the main building, in contact with the staircase, was damaged by cracks that had already been filled when we arrived. The staircase shows small cracks of a few centimeters towards the school yard.The damage to the building is level 1 for a vulnérabilité́ C.This picture was taken during the field mission that took place from December 5 to 11 following the earthquake of November 29, 2007 in Martinique. This earthquake was of magnitude 7.4 (MW), its epicenter being located in the north of the island, at sea. Trinidad is 36 km from the epicenter and the intensity of the tremors felt is between VI and VII on the European intensité́ EMS-98 scale.Martinique is, with Guadeloupe, classified in seismicity zone III (decree n°2007-1467 of October 12, 2007) which is the highest seismic hazard level for the French territory. From the point of view of intensities, with a maximum intensity of VI-VII, the earthquake of November 29, 2007 is the most important one felt in Martinique since the earthquake of June 8, 1999 (intensity VII). Macro-seismic intensity reached (in order of distance from the epicenter) VI-VII in the communes of Sainte-Marie, La Trinité, Fort-de-France, Le François, Trois Ilets, Le Marin and Sainte-Anne. The analysis of this earthquake mobilized many people, research laboratories and technical centers. The French Central Seismological Office has prepared a report based on the data processed by the Volcanological and Seismological Observatory of Martinique of the IPGP. The macro-seismic data were collected thanks to the survey forms distributed to the town halls and gendarmerie services by the SIDPC of the prefectures of Martinique and Guadeloupe, thanks to the testimonies filed on the BCSF website and thanks to the information collected during the BCSF field survey that took place from December 5 to 11, 2007. The BCSF's mission is to collect data on the earthquakes felt in France, to gather useful information and to facilitate its dissemination to the actors concerned by the seismic risk or conducting studies or research requiring the use of these observations. It is a member of the Transversal Seismicity Action of the Résif research infrastructure (French Seismological and Geodetic Network).Dégât au droit du raccordement de l'escalier de l'école Auguste Réjon sur la commune de La Trinité suite au séisme du 29 novembre 2007 en Martinique.L'Ecole Auguste Réjon (quartier Bonséjour) date des années 1960, c’est un bâtiment RC+2 sans vide sanitaire et sans sous-sol. Il comporte des joints de dilatation et possède une structure poteau-poutre en béton armé avec des remplissages en maçonnerie. Il est composé de deux bâtiments, formant un "L", reliés entre eux par un escalier et comprend pour chaque étage des balcons sur toute sa longueur.Le bâtiment n'a souffert du séisme que très localement, au niveau de l'escalier reliant les deux bâtiments. Celui-ci est en appui sur le bâtiment principal. Le mur extérieur du bâtiment principal, en contact avec l'escalier, a été endommagé par des fissures qui avaient déjà été colmatées lors de notre arrivée. L'escalier laisse apparaitre de petites fissures de quelques centimètres vers la cour de l'école.Les dégâts sur le bâtiment sont de niveau 1 pour une vulnérabilité́ C.Cette photo a été prise lors de la mission de terrain qui s'est déroulée du 5 au 11 décembre suite au séisme du 29 novembre 2007 à la Martinique. Ce séisme était de magnitude 7.4 (MW), son épicentre se situant au nord de l’île, en mer. Trinité se situe à 36 km de l’épicentre et l’intensité des secousses ressenties se situe entre VI et VII sur l’échelle d’intensité́ européenne EMS-98.La Martinique est, avec la Guadeloupe, classée en zone de sismicité III (décret n°2007-1467 du 12 octobre 2007) qui est le niveau d'aléa sismique le plus élevé pour le territoire français. Du point de vue des intensités, avec une intensité maximale de VI-VII, le séisme du 29 novembre 2007 est le plus important ressenti en Martinique depuis le séisme du 8 juin 1999 (intensité VII). L’intensité macrosismique a atteint (par ordre de distance à l'épicentre) VI-VII dans les communes de Sainte-Marie, La Trinité, Fort-de-France, Le François, Trois Ilets, le Marin et Sainte-Anne. L’analyse de ce séisme a mobilisé de nombreuses personnes, laboratoires de recherche et centres techniques. Le Bureau Central Sismologique Français a élaboré un rapport qui s’est appuyé sur les données traitées par l’Observatoire Volcanologique et Sismologique de Martinique de l’IPGP. Les données macrosismiques ont été collectées grâce aux formulaires d’enquête distribués auprès des mairies et des services de gendarmerie par le SIDPC des préfectures de Martinique et de Guadeloupe, grâce aux témoignages déposés sur le site Internet du BCSF et grâce aux informations recueillies lors de l’enquête BCSF sur le terrain qui s'est déroulée du 5 au 11 décembre 2007. Le BCSF a pour mission de collecter les données sur les séismes ressentis en France, de rassembler les informations utiles et de faciliter leur diffusion vers les acteurs concernés par le risque sismique ou menant des études ou recherches nécessitant l’usage de ces observations. Il est membre de l’Action transverse sismicité de l’infrastructure de recherche Résif (Réseau sismologique et géodésique français)