PRESEISMIC SIGNED

Project "PRESEISMIC" data sheet

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 Project objective

How do earthquakes begin? Answering this question is essential to understand fault mechanics but also to determine our ability to forecast large earthquakes. Although it is well established that some events are preceded by foreshocks, contrasting views have been proposed on the nucleation of earthquakes. Do these foreshocks belong to a cascade of random failures leading to the mainshock? Are they triggered by an aseismic nucleation phase in which the fault slips slowly before accelerating to a dynamic, catastrophic rupture? Will we ever be able to monitor and predict the slow onset of earthquakes or are we doomed to observe random, unpredictable cascades of events? We are currently missing a robust tool for quantitative estimation of the proportion of seismic versus aseismic slip during the rupture initiation, cluttering our attempts at understanding what physical mechanisms control the relationship between foreshocks and the onset of large earthquakes.

The current explosion of available near-fault ground-motion observations is an unprecedented opportunity to capture the genesis of earthquakes along active faults. I will develop an entirely new method based a novel data assimilation procedure that will produce probabilistic time-dependent slip models assimilating geodetic, seismic and tsunami datasets. While slow and rapid fault processes are usually studied independently, this unified approach will address the relative contribution of seismic and aseismic deformation.

The first step is the development of a novel probabilistic data assimilation method providing reliable uncertainty estimates and combining multiple data types. The second step is a validation of the method and an application to investigate the onset of recent megathrust earthquakes in Chile and Japan. The third step is the extensive, global use of the algorithm to the continuous monitoring of time-dependent slip along active faults providing an automated detector of the nucleation of earthquakes.