Fig. 7

Cumulative slip distribution during the period from 2018.5 to 2021.7 at 2 cm contour intervals. The green bold line indicates the outer edge of the subducted Kyushu-Palau Ridge (KPR) by Yamamoto et al. (2013). The gray area represents the area with an average resolution of 0.08 or less, as shown in Fig. 6. The gray lines represent isodepth contour lines of the upper surface of the PHS plate. The pink line represents the location of the mantle wedge corner (MWC), which coincides with the isodepth contour of 30 km. The yellow-green line represents the 350 °C isotherm of the upper surface of the subducted PHS plate by Ji et al. (2016). The solid blue area and the blue contour lines with 2 cm intervals represent the coseismic slip area and afterslip area of the October 19, 1996 Hyuga-nada earthquake, respectively (Yagi et al. 2001). The solid red and red contour lines with 2 cm intervals represent the coseismic slip area and afterslip area, respectively, of the December 3, 1996 Hyuga-nada earthquake (Yagi et al. 2001). The yellow‒green solid square indicates the epicenter of the Mw6.2 Hyuga-nada earthquake on May 10, 2019 together with its CMT solution. The small solid orange stars represent the epicenters of the shallow very long frequency earthquakes (VLFEs) reported by Asano et al. (2015) from January 1, 2010 to March 31, 2010. The small gray and red solid circles represent the epicenters of shallow tectonic tremors reported by Yamashita et al. (2015) from April 2013 to July 2013 and Yamashita et al. (2021) from March 2014 to February 2017, respectively