Surface Processes Can Influence the seismicity of Active Faults

Assessing seismic hazards remains one of the most challenging scientific issue in Earth sciences. Deep tectonic processes are classically considered as the only persistent mechanism driving the stress loading of active faults over a seismic cycle. Here we show with a mechanical model that surface processes also significantly influence the stress loading of faults at the timescale of a seismic cycle. Indeed, erosional unloading preceding or associated with a large earthquake increases the rate of inter-seismic Coulomb stress loading on thrust fault planes. Erosion rates of about 1 to 20 mm.yr-1, as documented in Taiwan, can raise the Coulomb stress by 0.1 to 2 bar on the nearby thrust faults over the inter-seismic phase. Our results show that mass transfers induced by surface processes in general can be the dominant mechanism for inter-seismic Coulomb stress loading of faults near the surface. In turn, surface processes can probably trigger shallow seismicity or favor the rupture of deep continental earthquakes up to the surface.