Coseismic slip distribution of the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) estimated based on GPS data— Was the asperity in Miyagi-oki ruptured?

Takeshi Iinuma,Yusaku Ohta,Mako Ohzono,Satoshi Miura

doi:10.5047/eps.2011.06.013

Abstract

We investigated the crustal deformation associated with the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) that occurred on March 11, 2011, along the plate boundary off Tohoku district, northeastern Japan, based on dense GPS observation. Coseismic displacements due to this event were applied to estimate the causal interplate slip by means of a geodetic inversion analysis. The major slip area is located around the asperities of the 1981 Miyagi-oki (M 7.2) and 2003 Fukushima-oki (M 6.8) earthquakes and the maximum slip is estimated as being up to 35 m. The estimated slip distribution suggests that the asperities of the Miyagi-oki earthquake in 1978 (M 7.4) that had not been ruptured during the Miyagi-oki earthquake in 2005 were ruptured as a part of the main shock fault of the 2011 off the Pacific coast of Tohoku Earthquake.

Highlights

The 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) occurred on 11 March, 2011, off the Pacific coast of Tohoku district, northeastern Japan, where the Pacific plate is subducting at a rate of about 70∼85 mm/year beneath the overriding continental plate (Altamimi et al, 2007)
Looking at the area of major slip shown by the contour of 30 m, it overlaps the asperities of the 1981 Miyagi-oki earthquake (Yamanaka and Kikuchi, 2004) and the 2003 Fukushima-oki earthquake (Yamanaka, 2003)
The total seismic moment obtained by integrating the distributed slip shown in Fig. 1 amounts to 4.0 × 1022 N m, which is equivalent to a moment magnitude of 9.0 and almost identical with the value determined by the Japan Meteorological Agency (JMA) (2011a)

Summary

Introduction

The 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) occurred on 11 March, 2011, off the Pacific coast of Tohoku district, northeastern Japan, where the Pacific plate is subducting at a rate of about 70∼85 mm/year beneath the overriding continental plate (Altamimi et al, 2007). We consider the problem as to whether the remaining asperities of the 1978 Miyagi-oki earthquake ruptured with the 2011 off the Pacific coast of Tohoku Earthquake, or not, based on land GPS observation data. We use GPS data to estimate coseismic slip distributions on the plate boundary by means of a geodetic inversion method.

Results

Conclusion