Persistent inelastic deformation in central Japan revealed by GPS observation before and after the Tohoku-oki earthquake

We analyze strain rate distribution in central-northeastern Japan based on continuous GPS data before and after the occurrence of the Great Tohoku earthquake (Mw9.0) on March 11th, 2011, focusing on the far-field response in the Niigata Kobe Tectonic Zone (NKTZ), an E-W contraction region along the Japan seacoast of central Japan. Wavelength decomposition of the strain rate on the E-W direction, calculated from GPS data, indicates that the long-wavelength pattern changed from preseismic E-W contraction to postseismic E-W extension, representing elastic response to plate interaction at the Japan Trench. However, the short wavelength patterns reveal a persistent localized contraction zone around northern NKTZ before and after the Tohoku-oki earthquake. The persistent localized deformation pattern can be reproduced by an aseismic slip on a fault cutting the lower crust and a part of the upper crust. These results demonstrate that an inelastic process plays an essential role in the deformation of the Japan island arc.