Fig. 2

Coseismic slips of historical earthquakes, slip-deficit rates, and gravity anomalies in the Nankai Trough region. a Areas of > 1 m inferred coseismic slip during the 1944 Tonankai (red) and 1946 Nankai (green) earthquakes (Baba and Cummins 2005), > 3 m slip during the 1946 Nankai earthquake (purple) (Murotani et al. 2015), and > 0.6 m slip during the 1968 Hyuganada earthquake (blue) (Yagi et al. 1998); colored stars indicate their epicenters. b Source segments of the 1854 Ansei Tokai (purple) and Nankai (brown) earthquakes whose amounts of average slips on segments are 4 m, 4 m, 4.6 m, and 6.3 m from the east (Aida 1981a, b). Blue outlines represent LSSE areas: (right to left) the 20-cm slip contour during 2001–2007 (Ozawa et al. 2016), the 4-cm slip contour during 2014–2017 (Kobayashi 2017), the ~ 6-cm contour of average sip during 2004–2005 (Takagi et al. 2016), and the 20-cm slip contour in 2003 (Geospatial Information Authority of Japan 2015). c Source of the 1707 Hoei earthquake whose amounts of average slips on segments are 5.6 m, 7.0 m, 5.6 m, 9.2 m, and 9.2 m from the east (Furumura et al. 2011); the easternmost area is doubtful (Matsu’ura 2012; Kobayashi et al. 2018). Broken gray lines are depth contours (10 km intervals) of the top of the subducting Philippine Sea plate (Hirose et al. 2008). d Slip-deficit rates (color) and direction of Philippine Sea plate motion (arrows) relative to the continental plate (Nishimura et al. 2018). The blue rectangle indicates the 2017–2018 LSSE (Yokota and Ishikawa 2020). Green dots indicate shallow VLFEs (Takemura et al. 2019). Purple outlines, from right to left, enclose source regions of Tokai earthquakes (Central Disaster Management Council 2001) and Tonankai and Nankai earthquakes (Earthquake Research Committee 2001). e Free-air gravity anomalies. Thick black lines indicate a subducted seamount and ridges (Deep-Paleo: Kodaira et al. 2004; Paleo-Zenisu: Kodaira et al. 2004, Park et al. 2003; Tosabae: Kodaira et al. 2000; Kyushu-Palau: Yamamoto et al. 2013). Open arrows indicate ridges not yet subducted. f Regional tectonic map showing locations of the study area (red box) and the top panel of Fig. 1 (blue box)