[J05-P] Poster

[J05-P-03] Spatiotemporal distribution of locking and aseismic slips prior to the 2011 Tohoku-oki earthquake

^○Momo Tanaka¹, Shoichi Yoshioka², Yukiko Nishino³ (1.Graduate School of Science, Kobe University, Kobe, Japan, 2.Research Center for Urban Safety and Security Kobe University, Kobe, Japan, 3.Panasonic Corporation, Kyushu Branch, Fukuoka, Japan)

We obtained the horizontal and vertical tectonic crustal deformation in the Tohoku district. We investigated GNSS data for seven years just prior to the 2011 Tohoku-oki earthquake (M9.0). We set the average displacement rate of three GNSS stations in Niigata prefecture as a reference. Chebyshev polynomials enabled high-precision estimation of the tectonic crustal deformation. We determined an optimal order of the polynomials, by minimizing AIC. After correcting offsets caused by coseismic crustal deformation and antenna exchange in the time series, we fitted logarithmic curve to horizontal data to eliminate the effects of postseismic crustal deformations of the following three large earthquakes: the 2003 Tokachi-Oki (M8.0), the 2005 Miyagi-Oki (M7.2), and the 2008 Iwate-Miyagi nairiku earthquakes. Then, we obtained the tectonic crustal deformation, by subtracting common-mode errors and the annual and semi-annual periodic signals from the time series. Then, we performed the inversion analyses for the tectonic crustal deformation with a time interval of one year, and estimated spatiotemporal interplate locking and aseismic slip distributions. We used the geometry model of the Pacific plate by Nakajima and Hasegawa (2006). We employed an inversion analysis which includes the following three prior constraints: the spatial slip distribution is smooth to some extent, slip directions are mostly oriented in the direction of plate convergence, and the temporal change in locking and slip distributions was smooth to some extent (Yoshioka et al., 2015). The results of our inversion analyses revealed locking of approximately 9 cm/year at the offshore of Miyagi prefecture during the period from 2004 to 2010, indicating strong interplate coupling. We also found that locking was 2 cm/year at the middle of offshore Sanriku in 2004, and it became gradually smaller and almost disappeared in 2010.