Index map of the Tohoku-oki subduction zone, NE Japan. The black line shows the location of the MY102 seismic survey line (Ito et al.2005; Miura et al.2005). The red star shows the epicenter of the great 2011 Tohoku-oki earthquake (Mw9.0) on March 11, 2011, which was determined by JMA, and green area indicates the large coseismic slip areas of the 1978 (Mw7.4) and 2005 (Mw7.2) Miyagi-oki earthquakes (Yamanaka and Kikuchi2004; Okada et al.2005). The coseismic slip area of the 1981 (Mw7.0) earthquake (Yamanaka and Kikuchi2004) is outlined by a blue line. The low-V and low- VP/VS domains observed beneath the plate interface (Matsubara and Obara2011) are indicated by orange ellipses. Iwa, Iwate; Miy, Miyagi; Fuk, Fukushima; Iba, Ibaraki Prefecture.