Distribution of earthquakes used in this study. (a) Vertical E-W cross section. (b) Map view. Gray and blue dots are shallow (depth < 40 km) and deep (depth > 40 km) earthquakes, respectively. Red triangles are quaternary volcanoes. The rectangular box in the overview map shows the approximate spatial extent of the focal area of the 2008 Iwate-Miyagi Nairiku earthquake. E-W lines are the locations of the E-W cross sections in Figures 3,4,5 and6.