Seismic characteristics of supershear and sub-Rayleigh earthquakes: Implication from simple cases

Numerous investigations of supershear earthquakes make a conclusion that a supershear earthquake produces a seismic shock wave on the ground that may increase the resulting destruction. We investigate a supershear rupture promoted by the free surface and find out that although the seismic energy of a supershear earthquake can be transmitted further with large amplitudes, the peak slip velocity on a fault near the free surface is smaller than that caused by a subshear rupture earthquake. Our results show that the free-surface-induced supershear rupture mitigates the amplitudes of ground motions near the fault plane compared with the subshear rupture. The Coulomb failure change derived from dynamic modeling further suggests that this free-surface-induced supershear reduces aftershock potential compared to a subshear rupture. Both ground motion at near-fault and aftershock possibility show low risk for the free-surface-induced supershear rupture earthquake than subshear earthquake, contrary to the traditional concept.