Magnetotelluric study of the Remiremont-Epinal-Rambervillers zones of migrationg seismicity, Vosges (France) (original) (raw)
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Bulletin de la Societe Geologique de France, 2012
The magnetotelluric method has been used to image the deep electrical structure of the Remiremont-Epinal-Rambervillers region in the French Vosges Massif, which has presented a significant seismic activity in the past decades. Several earthquakes of moderate magnitude (up to 5.1) occurred in this area with a systematic migration along a nearly N-S direction. Inversion of the magnetotelluric data reveals zones of high electrical conductivity. A large conductive body presents a significative spatial correlation with the region that was most recently affected by earthquakes. This conductive body is interpreted as a consequence of the presence of a fluid filled basement fault network in proximity to the zone affected by the last seismic crisis, where fluid pressure diffusion takes place for several years after the main shock and participates in maintaining a microseismic activity.
Seismotectonics in Northeastern France and neighboring regions
Comptes Rendus. Géoscience
The region of northeastern France is affected by low-magnitude background seismicity, with the rare occurrence of moderate earthquakes, which gives this region a non-negligible seismic risk. We provide an overview of the seismicity and seismotectonics of this intraplate domain and of its subregions: the Upper-Rhine Graben (URG), the external range and foreland of Jura, the Vosges, northern France and southern Belgium. Previously published catalogues over historical and instrumental times are used, and the epicentral distribution of earthquakes is compared to known tectonic structures, and the recently computed deformation field. Although no large earthquakes with M w > 6.0 occurred since the 1356 Basel seismic event (Io IX, MKS), the recent identification of active faults suggests periods of high seismic strain rates in the past. The origin of the seismic activity in each of these sub-regions, characterized by low to very-low strain rates, is attributed to pre-existing faults reactivated under specific natural or anthropogenic conditions.
Tectonophysics, 2005
We analyzed the seismicity of central and western France, using historical data, a compilation of all recorded earthquakes from 1962 to 2002 (4574 events, relocated), and all published focal mechanisms (119 focal solutions). The aim is to understand what are the causes of earthquakes and stress accumulation in a slowly deforming intraplate region. The distribution of earthquakes and focal mechanisms is first correlated with recognized faults, geological structures and tomographic images. Then, in order to better understand the distribution of hypocenters and seek deeper crustal sources for stress accumulation, Euler solutions are computed from the available Bouguer anomaly data. The analysis of the obtained pattern for heat flow values, provides a better understanding of the concentration of seismicity in some particular zones.
1998
Recherches sur le séisme du 18 février 1998 dans les grottes de la région de Saint-Paul-de-Fenouillet (Pyrénées Orientales, France). RESUME: Afin d'évaluer les effets d'un séisme sur le concrétionnement des grottes, huit cavités ont été visitées en France, dans les Pyrénées Orientales prés de Saint-Paul-de-Fenouillet après le séisme du 18 février 1996. Cet événement de magnitude 5,2 associé au mouvement d'une faille est-ouest à une dizaine de kilomètres de profondeur, a provoqué des dégâts de surface réduits. Les grottes choisies dans la zone épicentrale n'avaient pas été visitées depuis le séisme. Quelques dégâts y ont été observés. Il s'agit principalement de chutes de fistuleuses et de petits blocs. Parmi les cavités de la zone épicentrale, la plus intéressante est le Barrenc du Paradet qui est aligné sur une faille active récente. Il présente de nombreux dégâts ayant affecté les fistuleuses à la suite du séisme. On y observe aussi de très nombreux dégâts anciens. Parmi eux, des stalagmites cisaillées horizontalement et dont les différents tronçons, restés en place, sont décalés et ont subi une rotation. En l'absence d'autre explication ces formes pourraient être attribuables à des séismes passés. L'étude des fistuleuses qui sont de véritables pendules naturels peut donner des indications sur la direction et le seuil de l'amplitude du mouvement sismique ayant provoqué leur chute lors d'un séisme, permettant ainsi d'obtenir des informations pour calibrer les dommages engendrés par des séismes anciens. Une étude statistique montre que la direction principale des débris de fistuleuses est est-ouest. L'analyse des enregistrements accélérométriques recueillis au barrage de l'Agly montre une accélération amplifiée dans cette direction. Une modélisation confirme que les fistuleuses sont des objets relativement résistants mais qui peuvent rompre dans certaines conditions pendant un séisme.
Seismicity patterns in southwestern France
Comptes Rendus. Géoscience
Seismic monitoring of southwestern France began in the 1960s, and homogeneous coverage by observation networks has been in place since the 1990s. The accumulation of data now allows a refined understanding of regional seismicity, not only on its spatial aspects, but also on the regularity of the earthquake distribution over time. This paper is both a review of the work carried out on the subject, and a progress report on the current knowledge of the regional seismicity in its seismotectonic context. With the support of maps, the available catalogs are exploited at different nested scales, from the region as a whole to the numerous clusters that characterize the seismicity of southwestern France, and more specifically that of the Pyrenees. An exhaustive study of these Pyrenean clusters and their temporal behavior is proposed, allowing in particular a better description of the prominent seismicity stripe to the northwest of the range.
Geophysical Journal International, 2000
Focal mechanism solutions are determined for 11 small intraplate earthquakes that occurred between 1990 and 1998 in Normandy and the Channel Islands. These mechanisms are obtained from the P-wave ®rst-motion polarities recorded by stations from local and regional seismic networks. The accuracy of each hypocentral location is closely examined and the quality of each fault plane solution is discussed by considering the in¯uence of the velocity structure. The predominant feature of the computed focal mechanisms is the relatively widespread near-horizontal NE±SW Taxis orientation. Horizontal P-axes strike roughly NW±SE. Mechanism solutions for the earthquakes in the Avranches region show left-lateral strike slip on a NNW±SSE fault zone. For the overall region, it seems that nodal planes of normal faulting solutions trend NW±SE or WNW±ESE, whereas those of thrust faulting solutions trend NE±SW. This is in agreement with the general regional stress pattern. The NE±SW normal fault plane solution of the 1990 Jersey event is unique because it is not consistent with the regional style of faulting.
Bulletin de la Societe Geologique de France, 2011
The lower Var valley is the only large outcropping zone of Plio-Quaternary terrains throughout the southwestern Alps. In order to assess the seismic hazard for the Alps -Ligurian basin junction, we investigated this area to provide a record of earthquakes that have recently occurred near the city of Nice. Although no historical seismicity has been indicated for the lower Var valley, our main objective was to identify traces of recent faulting and to discuss the seismogenic potential of any active faults. We organized multidisciplinary observations as a microseismic investigation (the PASIS survey), with morphotectonic mapping and imagery, and subsurface geophysical investigations. The results of the PASIS dense recording survey were disappointing, as no present-day intense microseismic activity was recorded. From the morphotectonic investigation of the lower Var valley, we revealed several morphological anomalies, such as drainage perturbations and extended linear anomalies that are unrelated to the lithology. These anomalies strike mainly NE-SW, with the major Saint-Sauveur -Donareo lineament, clearly related to faulting of the Plio-Pleistocene sedimentary series. Sub-surface geophysical investigation (electrical resistivity tomography profiling) imaged these faults in the shallow crust, and together with the microtectonic data, allow us to propose the timing of recent faulting in this area. Normal and left-lateral strike-slip faulting occurred several times during the Pliocene. From fault-slip data, the last episode of faulting was left-lateral strike-slip and was related to a NNW-SSE direction of compression. This direction of compression is consistent with the present-day state of stress and the Saint-Sauveur-Donareo fault might have been reactivated several times as a left-lateral fault during the Quaternary. At a regional scale, in the Nice fold-and-thrust belt, these data lead to a reappraisal of the NE-SW structural trends as the major potentially active fault system. We propose that the Saint-Sauveur-Donareo fault belongs to a larger system of faults that runs from near Villeneuve-Loubet to the southwest to the Vésubie valley to the north-east. The question of a structural connection between the Vésubie -Mt Férion fault, the Saint-Sauveur-Donareo fault and its possible extension offshore through the northern Ligurian margin is discussed.