The Origin of Large, Long-Period Near-Fault Ground Velocities During Surface-Breaking Strike-Slip Earthquakes

Abstract

Records of near-fault ground motions from recent surface-breaking earthquakes are characterized by large (> a few m/s), long-period (a few seconds) ground velocity pulses, which may pose significant hazard for tall buildings and large infrastructures. Yet, the generation mechanism is not well understood. Here, using spontaneous rupture simulations, we examine the origin of large velocity pulses observed during the 2016 Mw7.0 Kumamoto (Japan) earthquake. We show that near-fault waveform data as well as seismologically estimated moment and radiated energy can be well reproduced by a relatively simple model with uniform along-strike pre-stress and frictional properties. Our results suggest that large, long-period ground velocities are caused by the dynamic interaction of propagating rupture and the Earth's surface, which is enhanced by reflected waves from the boundaries of low-velocity layers. Such a generic mechanism suggests that large, long-period ground motion is a common occurrence in near-fault regions during surface-breaking, strike-slip earthquakes.