Post-large earthquake seismic activities mediated by aseismic deformation processes

Two aseismic deformation processes are commonly invoked to explain the transient geodetic surface displacements that follow a major earthquake: afterslip and viscoelastic relaxation. Both induce time dependent stress variations in the crust, potentially affecting aftershock occurrence. However, the two mechanisms’ relative impacts on crustal deformation and seismicity remain unclear. We find for the case of the 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake not only that afterslip likely drove clustered seismicity after the earthquake, but also that long-range earthquake interactions were likely modulated by viscoelastic relaxation at large scales in space (>5 times the fault rupture length) and time (>7 yr). This has important implications for the study of the “seismic cycle” and for seismic hazard estimation, since post-seismic deformation related to a single Mw 7.2 earthquake affects interseismic velocities and regional seismicity rates for more than a decade.