Off-fault damage patterns due to supershear ruptures with application to the 2001 Mw 8.1 Kokoxili (Kunlun) Tibet earthquake

We extend a model of a two-dimensional self-healing slip pulse, propagating dynamically in steady state with slip-weakening failure criterion, to the supershear regime in order to study the off-fault stressing induced by such a slip pulse and investigate features unique to the supershear range. Specifically, we show that there exists a nonattenuating stress field behind the Mach front that radiates high stresses arbitrarily far from the fault (practically this would be limited to distances comparable to the depth of the seismogenic zone), thus being capable of creating fresh damage or inducing Coulomb failure in known structures at large distances away from the main fault. We allow for both strike-slip and dip-slip failure induced by such a slip pulse. We show that off-fault damage is controlled by the speed of the slip-pulse, scaled stress drop, and principal stress orientation of the prestress field. We apply this model to study damage features induced during the 2001 Kokoxili (Kunlun) event in Tibet, for which it has been suggested that much of the rupture was supershear. We argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture. However, those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault. We also make some estimates of fracture energy which, for a given net slip and dynamic stress drop, is lower than for a sub-Rayleigh slip pulse because part of the energy fed by the far-field stress is radiated back along the Mach fronts.