Aftershock activity of the 2011 off the Pacific coast of Tohoku earthquake and the 2011 off Ibaraki earthquake revealed by CMT inversion using dense short period OBS array
Abstract
To better understand the aftershock activity of the 2011 Ibaraki-oki earthquake, which is the largest aftershock that occurred approximately 30 minutes after the 2011 off the Pacific coast of Tohoku earthquake (the 2011 Tohoku-oki earthquake), we conducted a centroid moment tensor (CMT) inversion analysis incorporating a local 3-D seismic velocity model for aftershocks in the off Ibaraki region to reveal the stress field using high-frequency (0.4-1.0 Hz) seismograms acquired by a dense short-period OBS array. Higher-frequency analysis and the dense OBS array made it possible to obtain 536 CMT solutions for small-to-moderate earthquakes with high spatial resolution. Then, we investigated the relationship between CMT solutions of aftershocks and tectonic environments in the off Ibaraki region. The aftershock activities in the off Ibaraki region are classified into five groups: (1) thrust earthquakes, separated by the large slip area of the 2011 Ibaraki-oki earthquake and the tectonic tremors, (2) intraslab strike-slip earthquakes located to the north of the fault area of the 2011 Ibaraki-oki earthquake, (3) intraslab normal-fault earthquakes suggesting the tensional stress field within the subducting Pacific plate due to the plate bending imposed by the overriding Philippine Sea plate, (4) earthquakes with various mechanisms above a subducting seamount suggesting 3-D complex fracture networks and (5) normal-fault earthquakes shallower than the interplate earthquakes. To discuss the aftershock activities, we calculated the Coulomb failure function caused by the 2011 Ibaraki-oki earthquake. The aftershock distribution could be mainly explained by the Coulomb failure function except for the normal-fault earthquakes shallower than the interplate earthquakes. These earthquakes might be explained by the stress field introduced by the seamount subduction and the afterslip in the trench side after the 2011 Tohoku-oki earthquake.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.T31A..10Y