Fig. 1From: Isolated intermediate-depth seismicity north of the Izu peninsula, Japan: implications for subduction of the Philippine Sea PlateTectonic setting of central Japan with seafloor topography. Pink and blue lines denote iso-depth contours of the PHS Plate (Hirose et al. 2008; Nakajima et al. 2009) and Pacific Plate (Nakajima et al. 2009), respectively. Green shading represents an area where the bottom of the PHS Plate is in contact with the upper surface of the Pacific Plate (Nakajima et al. 2009; Uchida et al. 2009). Black triangles denote active volcanoes. Red squares represent the epicenters of thrust earthquakes that occurred along the upper surface of the PHS Plate. The red star denotes the epicenter of the M3.1 earthquake analyzed in this study. The focal mechanism of the M3.1 earthquake, as determined by the Japan Meteorological Agency (JMA), is shown in an equal-area lower-hemisphere projection. Gray arrow shows the relative plate motion of the PHS Plate with respect to the continental plate. The rectangle shows the area highlighted in Fig. 2aBack to article page