Result of S-wave perturbation. E-W vertical cross sections are shown. Location of each cross section (A-L) is shown in the insert map. Black and white circles are shallow earthquakes that occurred after and before the 2011 Tohoku-Oki earthquake, respectively. White star denotes the hypocenter of the 2008 Iwate-Miyagi Nairiku earthquake. Black and white crosses are the deep low-frequency earthquakes that occurred after and before the 2011 Tohoku-Oki earthquake, respectively. Red triangles are quaternary volcanoes. Red squares are the locations of the active faults. The dashed line near the bottom of the figure shows the depth of the Moho discontinuity (Zhao et al. 1990).