Fig. 1

Tectonic setting of the Kinki Triangle, western Japan. (a) Distribution of active faults (red lines) and the Kinki Triangle (yellow) after National Institute of Advanced Industrial Science and Technology (2012). Shaded relief and bathymetry (10-m and 500-m horizontal grid-spacing, respectively) are based on digital elevation map by the Geospatial Information Authority of Japan. White triangles: Quaternary volcanoes (Committee for Catalog of Quaternary Volcanoes in Japan 1999). Box shows location of study area closed-up in Fig. 2a. Dotted line shows location of cross-section in Fig. 1c. (b) Interseismic secular velocity at onland GNSS and offshore GPS-A stations modified from Nishimura et al. (2018). Vectors are velocities relative to the stable Amurian plate with 95% confidence limit ellipsoids (Nishimura et al. 2018). The shaded yellow region and pink line are the Niigata–Kobe Tectonic Zone (Sagiya et al. 2000) and the Median Tectonic Line, respectively. Depth contour (km) of the upper boundary of the Philippine Sea and Pacific Plates are from Nakajima and Hasegawa (2007). (c) Schematic cartoon of the E–W cross-section and inferred geometry of faults at ~ 34°N based on previous studies modified after Sato et al. (1998, 2009). Shaded gray: sedimentary basin in this region. OsF: Osaka Bay Fault. KaF: Kariya Fault. NoF: Nojima Fault. UeF: Uemachi Fault. IkF: Ikoma Fault. NbF: Nara Basin East Edge Fault. TgF: Taguchi Fault. IsF: Isshi Fault. YiF: Yokkaichi Fault. The upper/lower crust boundary is inferred at the downdip limit of the seismogenic zone (cross-hatched area) (e.g., Tanaka 2004). A possible detachment is speculated. Box shows region of study area closed-up in Fig. 2a