Slow and Fast Slip Dynamics From Fracture Networks

Abstract : Active faults release elastic strain energy via a whole continuum of modes of slip, ranging from devastating earthquakes to Slow Slip Events and persistent creep. Understanding the mechanisms controlling the occurrence of rapid, dynamic slip radiating seismic waves (i.e. earthquakes) or slow, silent slip (i.e. SSEs) is a fundamental point in the estimation of seismic hazard along subduction zones. On top of showing slower rupture propagation velocity than earthquakes, SSEs exhibit different scaling relationships, which could reflect either different physical mechanisms or an intriguing lack of observations.  Like earthquakes, SSEs are bound to occur along unstable portions of active faults, raising the question of the physical control of the mode of slip (seismic or aseismic) along these sections. Here, we use the numerical implementation of a simple rate-weakening fault model to explain the spontaneous occurrence, the characteristics and the scaling relationship of SSEs and earthquakes. Our unified framework only accounts for the geometrical complexity of fault networks and associated stress perturbations, leading to the emergence of all modes of slip from earthquakes to SSEs without appealing to complex rheologies or mechanisms. Our model helps resolving many of the existing paradoxes between observations and physical models of earthquakes and SSEs and reproduces all episodes of fault slip in nature, including those unexplained yet.

Bio : Dr Harsha Bhat is a CNRS scientist at the Laboratoire de Géologie in Ecole Normale Supérieure in Paris. He received his PhD in mechanics from Harvard University, USA in 2007, and was a post-doctoral associate at University of Southern California and Caltech prior to moving to Paris in 2012. His research interests are related to fracture mechanics, elasto-dynamics, geomechanics and in particular the mechanics of faulting, especially the importance of fault zone geometry, and off-fault damage during earthquakes.