Fig. 1

The distribution of the Niigata–Kobe Tectonic Zone. a Major Quaternary faults and the NKTZ in Japan. The Japanese Islands are surrounded by the Japan Sea and the Pacific Ocean. The Japanese Islands lie on four plates: the Amurian plate (AP), the North American plate (NAP), the Philippine Sea plate (PSP), and the Pacific plate (PP) (e.g., Wakita 2013), with plate boundaries shown as thick black lines. Fine red lines indicate Quaternary faults as given by Research Group for Active Faults of Japan (1991). The blue region shows the distribution of the Niigata–Kobe Tectonic Zone (e.g., Sagiya et al. 2000). The small rectangle indicates the central NKTZ (b). b The Quaternary faults around the NKTZ. Solid red lines show the distribution of the major Quaternary faults (the Ushikubi Fault and the Atotsugawa Fault) in the central part of the NKTZ. Dashed red lines show the distribution of the Quaternary faults except the major Quaternary faults (the Ushikubi Fault and the Atotsugawa Fault) as given by Research Group for Active Faults of Japan (1991). Dashed blue box shows the distribution of the Takayama Fault Zone. Thick dashed black line shows the southern margin of the Takayama Fault Zone (we regarded it as the southern margin of the NKTZ). The black box is corresponding to the area of Fig. 2