The Criticality of Coulomb Wedge and Efficiency of Tsunami Generation
Wednesday, May 8th, 2013,
The classic critical taper theory has long been used to describe the stress state and deformational processes within accretionary wedges in shallow subduction zones. The critical wedge taper is attained when material is on the verge of Coulomb failure everywhere under horizontal compression, including the basal decollement. Unlike most of earthquake modeling work where off-fault material is treated elastic, we incorporate the critical state of the overriding wedge. We show that for a wedge on the verge of failure pore pressure increase due to updip rupture on a shallow dipping fault causes extensive failure within the wedge, which gives rise to slow rupture velocity, depletion of high-frequency radiation, low moment-scaled radiated energy, and significant seafloor uplift landward from the trench. This model solves many paradoxes about shallow subduction earthquakes. By exploring different strength parameters corresponding to different wedge criticality we show that the efficiency in generating seafloor uplift (and tsunamis) consistently increases, as the wedge is closer to failure initially.