Updip and Along-Strike Aftershock Migration Model Driven by Afterslip: Application to the 2011 Tohoku-Oki Aftershock Sequence

We present an analytical model based on the idea that afterslip drives seismicity: aftershocks occur when a given level of afterslip is reached in their vicinity. Afterslip is assumed to be governed by a resisting stress that increases as the logarithm of the sliding velocity. This model extends the aftershock migration model of Perfettini et al. (2018, ), limited to along-strike migration and the early postseismic phase, to any migration direction (in particular the along-dip migration) and any time of the postseismic phase. This model is able to capture most of the features of aftershock migration such as the increase of the aftershock region as the logarithm of time and the observed aftershock migration velocities. When applied to the aftershock sequence of the Tohoku-Oki earthquake, our model is able to describe the expansion of the aftershock region in both strike and dip directions together with the observed variations of migration velocities. Plain Language Summary Aftershocks are shown to migrate with time away from the rupture area of the mainshock. We present here a model based on the idea that afterslip drives aftershocks. The model is able to predict observed aftershock migrations both along the strike and dip directions of the fault. We show that the aftershock zone expand as the logarithm of time and predict apparent propagation velocities consistent with the observations. The model is able to explain most of the features of the aftershock sequence of the Tohoku-Oki earthquake.