Fig. 7

A belt of upper-plane seismicity in the slab crust. a Hypocenter distribution of earthquakes in the crust of the Pacific Plate subducting under eastern Japan. Events 0–10 km below the upper plate surface are shown by red dots. Bold arrows denote estimated locations of the upper-plane seismic belt. The contact zone between the Philippine Sea and Pacific Plate beneath Kanto and that between the subducted crust and the Pacific Plate beneath western Hokkaido are indicated by blue thick broken curves. Solid curves, red triangles, and gray stars denote iso-depth contours of the upper plate surface, active volcanoes, and small repeating earthquakes, respectively. b–l Frequency distributions of upper-plane events along the lines b through l in Fig. 7a plotted against depth. Frequency is plotted for intervals of 10 km. The black arrows show the peak that corresponds to the upper-plane seismic belt. (After Kita et al. 2010)