Coseismic and postseismic crustal deformation after the Mw 8 Tokachi-oki earthquake in Japan

The permanent Global Positioning System (GPS) array in Japan detected coseismic and postseimic deformation of the 2003 Tokachi-oki earthquake (Mw 8). We estimate the time evolution of its postseismic slip, together with its coseismic slip distribution. The result shows that the postseismic slip has been occurring mainly in an area adjacent to the coseismic slips, propagating to the northeast and southwest. This suggests that, as of March 6, 2004, the postseismic slip of the strongly coupled area neighboring the coseismic rupture partly released seismic moment, equivalent to an earthquake of Mw 7.8.