Static stress drop in the <i>M_w</i> 9 Tohoku‐oki earthquake: Heterogeneous distribution and low average value

Abstract

Abstract Static stress drop distribution and its average value over the rupture area contain important information on the mechanics of large earthquakes. Here we derive static stress drop distributions from 40 published rupture models for the 2011 M w 9 Tohoku‐oki earthquake that are based on various multidisciplinary observations. Average stress drop value over the fault area encompassed by the 5 m coseismic slip contour is not unusually large for each rupture model; the mean for the 40 models is 2.3 ± 1.3 MPa, assuming a uniform rigidity 40 GPa. The value for the entire rupture zone and with a more realistic rigidity structure will be even lower. In the majority of the models, local stress drop in parts of the rupture zone well exceeds 20 MPa. The heterogeneous stress change distribution, with large stress drop being accompanied by large stress increase, leads to the small average for the earthquake.