Relationships between inherited crustal structures and seismicity in the Western Alps inferred from 3D structural modeling
Relationships between inherited crustal structures and seismicity in the Western Alps inferred from 3D structural modeling (in Geodynamics of the France Southeast Basin; importance of gravity tectonics, Xavier Le Pichon (editor) and Claude Rangin (editor))
Bulletin de la Societe Geologique de France (November 2010) 181 (6): 583-590
We developed a 3-D structural model of a key area in the southwestern Alps, at the boundary between the external and internal zones. Six geological bodies are analyzed: internal and external basements, Brianconnais and Piemontais zones (internal sedimentary cover nappes), exotic flyschs, and external sedimentary cover. 3D volumes of each geological body are modeled using the structural map of the area projected on the Digital Elevation Model (DEM) and 5 cross-sections. The global model is interpolated from the map, DEM, and cross sections, using the potential field method, and represented by a Voronoi diagram. The final 3D-model is used as a structural frame to plot the earthquakes of the GeoFrance3D database, allowing to precisely and quantitatively investigate the relationships between crustal structures and current seismic activity of the belt. The boundary between external and internal zones corresponds to the so-called Crustal Penninic Thrust (CPT), which is a former Oligocene major thrust. Our model establishes that this former thrust represents the western limit of the seismic activity along the Brianconnais seismic arc, currently undergoing extensional tectonics.