Dynamic wedge failure reveals anomalous energy radiation of shallow subduction earthquakes

Dynamically induced Coulomb failure in the overriding wedge significantly affects energy radiation of shallow subduction earthquakes. For a wedge on the verge of failure, extensive fluid-assisted coseismic failure due to updip rupture causes significant seafloor uplift above a shallow dipping basal fault. The large inelastic uplift, greatly enhanced by the presence of free surface, significantly dilates the fault behind the rupture front during the rupture propagation, which reduces the effective normal stress and sliding friction on the fault, and increases the dynamic stress drop and slip velocity. As a result, slip-velocity time histories in the shallow section of the fault tend to have a ‘snail-like’ shape, leading to depletion of high frequencies in the slip velocity field and the resultant source time function. We also show that the failure in the wedge acts as a large energy sink (while contributing to seismic moment), giving rise to distributed heat generation (i.e., small heat flow anomaly across the fault), low moment-scaled radiated energy, slow rupture velocity, and small directivity, which provides a unifying interpretation for nearly all anomalous observations documented for shallow subduction earthquakes.