The evolution of the Earth's topography is dictated by the interactions between tectonics, climate and surface processes. Whether this evolution influences tectonic deformation over geological times (1-10 Myr) has been largely debated, without converging towards clear conclusions. At intermediate time scales (10 kyr - 1 Myr), both erosion and subsequent isostatic rebound are suggested to enhance slip rate of faults. Here we use a simple mechanical model to show that surface processes most significantly influence fault dynamics at the timescale of a seismic cycle (0.1-10 kyr). Indeed, erosional unloading preceding or associated with an earthquake increases the rate of inter-seismic Coulomb stress loading on frictional fault planes. For instance, erosion rates of ~10 mm.yr-1, as documented in Taiwan, are sufficient to raise the Coulomb stress by 1-10 bar on the nearby thrust faults over the inter-seismic phase. Our results show that surface processes are the dominant inter-seismic Coulomb stress loading factor of faults near the surface. This suggests that stresses induced by surface processes could lead to shallow seismicity or aseismic slip, or even provide additional energy and slip to deep continental earthquakes, allowing them to rupture up to the surface.
Funding: INSU, ORCHID program