Stress state in the largest displacement area of the 2011 Tohoku- Oki Earthquake
Résumé
Observations of a maximum coseismic slip of >50 m near the trench support inferences of a wholesale change in the stress regime and a nearly total stress drop during the 2011 Tohoku earthquake. We tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the Integrated Ocean Drilling Program approximately one year after the earthquake. On the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts, we conclude that in situ horizontal stress was reduced during the earthquake, consistent with coseismic fault weakening and a nearly total stress