Fig. 1.

(a) Tectonic setting of Japanese island. Solid lines indicate plate boundaries. EU, PH, PA, and NA denote Eurasian, Philippine Sea, Pacific and North American plates, respectively. (b) Magnified map of the rectangular area in Fig. 1(a). The solid square denotes the borehole station of the Sacks-Evertson strainmeter. The solid star denotes the epicenter of the 1952 Tokachi-oki earthquake. Open big and small stars denote the epicenters of the 2003 Tokachi-oki earthquake and its largest aftershock, respectively. Color scale shows the cumulative afterslip for 5 hours following the main shock (Fukuda et al., 2009). Contours with a 1-m interval represent the coseismic slip distribution of the main shock estimated by Miyazaki and Larson (2008). The thick arrow shows the relative motion of the Pacific plate with respect to the North American plate computed based on the work of DeMets et al. (1994).