Epicenter of the 2011 Tohoku Earthquake (red star), W-phase MT solution by USGS, and stations that recorded the tsunami. Triangles, diamonds and squares indicate the locations of coastal (tide or wave) gauges, offshore GPS wave gauges and ocean-bottom tsunami sensors or DART (Deep-ocean Assessment and Reporting of Tsunamis) systems, respectively. Colors indicate operating agencies (yellow: Japan Meteorological Agency (JMA), blue: Japan Coast Guard (JCG), green: Japan Agency for Marine-Earth Science and Technology (JAMSTEC), orange: National Oceanic & Atmospheric Administration (NOAA), light blue: Japan’s Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS), and purple: University of Tokyo). The thin rectangle indicates the region shown in Fig. 3.