Fig. 8

Relationship between shallow slow earthquakes and subsurface seismic structures. a S-wave velocity perturbations 5–10 km below sea level beneath the DONET stations (Tonegawa et al. 2017). b Cross-section of reflection profile (Tsuji et al. 2014) and high-resolution receiver function image southeast off the Kii Peninsula (Akuhara et al. 2020). c Schematic figure from the interpretation of Akuhara et al. (2020). We modified Fig. 3 of Tonegawa et al. (2017) and Fig. 4 of Akuhara et al. (2020). Colored dots and stars in a and c are hypocenters of shallow VLFEs (Sugioka et al. 2012; Nakano et al. 2018a). Light blue, yellow, pink, orange, red, and light green layers in b represent seabed sediment, accreted sediment, upper underthrust sediment, lower underthrust sediment, incoming sediment, and oceanic crust, which are interpretations of velocity structures from receiver function images. Locations of KMC09 and KMD13 are shown in a