The Early POSTseismic deformation: A key process in the earthquake cycle. From observation to modeling. – E-POST

Earthquake occurrence is mainly controlled by the time evolution of crustal stress. Postseismic transient processes strongly contribute to stress redistribution after an earthquake and to the generation of catastrophic seismic sequences. It is thus crucial to understand their complex space and time evolution to better assess seismic hazard. Our project addresses this critical question through geodetic and seismological observations, and numerical models. The novelty of the project is that we will focus on the early postseismic phase (seconds to days), on which little work has been done so far. We will investigate the relationship between the early postseismic phase and coseismic rupture in space and time, and its impact on longer deformation time scales. We will take advantage of the increase of seismological and space geodetic observations concerning active faults (e.g. network densification, High Rate GPS data) to document the early postseismic deformation with unprecedented details and to interpret them jointly. Secondly, various spatio-temporal kinematic modeling and inversions will provide major results on the co- to postseismic slip transition on the fault, in particular the timing of the phenomena and the spatial correlation or anti-correlation of seismic and aseismic slip. These constraints are required to implement and discuss mechanical models describing the behavior of the faults and the surrounding medium, with the ultimate goal of providing new insight into the physical parameters controlling fault slip and ruptures. The strength of the project resides both in the developed scientific strategy, implementing an integrated approach going from observation to kinematic description to mechanical interpretation, and in the interdisciplinary working group we have set up comprising (mostly young) scientists with recognized skills ranging from geodesy, seismology, hydromechanics and crustal mechanics.