Fig. 1

Tectonic setting of the study area and locations of seismic stations. a Blue and brown contours show the depths of upper boundaries of the PHS (Uchida et al. 2010) and the PAC (Nakajima et al. 2009), respectively. The black dashed line denotes the northeastern limit of the PHS (Uchida et al. 2009). Source areas of the 1703 Genroku Kanto and 1923 Kanto earthquakes are indicated by gray and green lines, respectively (Matsu’ura et al. 2007; Sato et al. 2016). The area of slow slip events is shown in yellow (Hirose et al. 2014). Black lines with triangles represent trench axes. Black arrows indicate the motion of PAC and PHS with respect to the NA (DeMets et al. 2010). b Locations of seismic stations. White and gray triangles indicate OBSs of JAMSTEC and ERI, respectively, while gray squares indicate stations operated by NIED. Small gray dots are earthquake epicenters determined by JMA between October 2011 and March 2013. Earthquake selection areas are delineated by black lines while black dots are epicenters determined by JMA and analyzed in this study