Focal depths and mechanisms of Tohoku-Oki aftershocks from teleseismic P wave modeling

Abstract

Aftershocks of the 2011 Tohoku-Oki great earthquake have a wide range of focal depths and fault plane mechanisms. We constrain the focal depths and focal mechanisms of 69 aftershocks with M w [ 5.4 by modeling the waveforms of teleseismic P and its trailing near-surface reflections pP and sP. We find that the ''thrust events'' are within 10 km from the plate interface. The dip angles of these thrust events increase with depth from *5°to *25°. The ''non-thrust events'' vary from 60 km above to 40 km below the plate interface. Normal and strike-slip events within the overriding plate point to redistribution of stress following the primary great earthquake; however, due to the spatially variable stress change in the Tohoku-Oki earthquake, an understanding of how the mainshock affected the stresses that led to the aftershocks requires accurate knowledge of the aftershock location.