Fig. 3

Reflection strengths along NS vertical planes [X = − 23.25 (a), −12.75 (b), −3.75 (c), 5.25 (d), and 15.75 (e)]. The color scale is shown in the upper right side. Locations of the planes are shown in the map on the upper left side. In the map, contours show the number of data at depth of 26 km assigned to each block. Thick blue lines show contours for 50,000, and thin blue lines are for contour intervals of 2000. When we draw contours, we interpolate the number of data. Black dots, green stars and red lines indicate hypocenters of ordinary earthquakes and low-frequency earthquakes (LFEs), and active faults, respectively. In the vertical planes, hypocenters occurring within 5 km of each plane are plotted, and blue lines indicate the contours of 10,000 for the number of data