Rose diagrams showing the distribution of shear-wave-splitting fast directions determined using the cross-correlation method. Earthquakes before and after the 2011 Tohoku earthquake are shown in (a) and (b), respectively. Red circles represent epicenters of earthquakes that occurred after the 2011 Tohoku earthquake (shown in Fig. 1(b)), indicating the extent of the area of increased seismicity. Red dotted lines indicate the maximum stress-axis direction (Kaneshima, 1990) and the thick black dashed line is the Tanakura Tectonic line.