Fig. 1.

Variable slip model of the Tohoku-oki Earthquake (black contour) based on continuous Global Positioning System (GPS) observation (Ozawa, personal communication). The black and white stars indicate the epicenters of the mainshock (M 9.0), and large aftershocks (M ≥ 7.0) that occurred within 40 minutes. GPS observation data including this period was used to estimate coseismic displacement. The orange and yellow stars indicate the epicenters of the earthquake near the boundary between Nagano and Niigata prefectures of March 12 (M 6.7), and the Eastern Shizuoka earthquake of March 15 (M 6.4) from the JMA PDE catalog. The focal mechanisms are based on JMA. The green circles indicate the epicenters of earthquakes occurring within seven days after the mainshock (M ≥ 3.0, depth ≤ 100 km). The dashed-rectangle region is the target region where the ACFF values were calculated. The thin line indicates the boundary between prefectures.