Segmentation des failles et interactions entre segments : un point de vue sismologique
École Normale Supérieure
Segmentation within seismogenic zones is defined by geometrical heterogeneities, stress and strength variability, impedance contrasts, material properties, thermal state and hydration. Fault zone complexity controls deformation processes at different time and space scales, i.e.: (1) earthquake interactions and seismic cycle; (2) spatio-temporal distribution of transient slip events (earthquakes, tremors, slow-slip); (3) rupture style and radiation properties of large earthquakes. Here we illustrate the contribution of seismological observation in characterizing fault segmentation and segment interactions, from the study of background seismic activity and of the rupture process of large earthquakes. We focus on three different tectonic contexts: (1) The NE Japan Trench, where the study of the radiation properties of the 2011, Mw 9.0 Tohoku earthquake and of pre-Tohoku seismic activity evidences along-dip and along-strike variability of fault zone properties, linked to the peculiar thermal state (cold slab) and the geometry of this subduction; (2) The diffuse deformation zone of Wharton Basin, with the observation of the 2012, Mw 8.6 multi-segment earthquake, involving dynamic triggering and possible reactivation of oceanic fracture zones; (3) The south margin of the Scotia Sea Plate, where we provide the first observation of very short recurrence time (10 years) between two major earthquakes (Mw 7.6 and 7.8) affecting the same fault segment. This challenges the classical hypothesis of long interseismic phases terminated by major events.