Fig. 4

Distribution of centroid–moment tensors (CMTs) with M > 3.5 from June 1, 2003 to September 30, 2011 (Hasegawa et al. 2012). CMTs in a and b represent interplate events, those in c and d represent upper plate events, and those in e and f represent lower plate events. The upper and lower panels in each pair show the CMTs before and after the 2011 Tohoku-Oki earthquake, respectively. Blue, green, red, and black beach balls denote normal, strike-slip, thrust, and other types of focal mechanisms, respectively. The contours in b show the mainshock slip distribution (Lay et al. 2011). The yellow dashed line shows the down-dip limit of the Philippine Sea Plate (Uchida et al. 2009). The thick red line shows the trench axis