Fig. 1

Tectonic setting of central Japan. The Niigata–Kobe Tectonic Zone (NKTZ) (Sagiya et al. 2000) is denoted by purple shading. Black triangles represent active volcanoes, and orange stars denote epicenters of earthquakes (M ≥ 6.5) that occurred at depths of ≤20 km during 1923–2015. Gray lines denote active faults. The Itoigawa–Shizuoka Tectonic Line (ISTL) is shown by green curve. Names of regions discussed in the text are labeled