Location map of the Japan Trench and the index of 12 profiles from seismic surveys. Location map of the Japan Trench and the index of 12 profiles from seismic surveys across the trench axis before the 2011 Tohoku-Oki earthquake. The names of lines match the names of survey lines managed by JAMSTEC. The star represents the epicenter of the earthquake. The yellow ellipses represent the slip areas of past major earthquakes and the estimated ages are given (Tajima et al. ). A simple contour represents the slip area of the 2011 Tohoku-Oki earthquake (Chester et al. ).