Fig. 1

Tectonic setting of the Kyushu island, Japan. The light blue and yellow stars and focal spheres denote the hypocenters and focal mechanisms of the mainshock and largest foreshock of the 2016 Kumamoto earthquake. The red triangles denote active volcanoes. The black lines denote the iso-depth contours of the upper surface of the Philippine Sea plate (Hashimoto et al. 2004). The brown lines indicate active faults. The red letters in the inset indicate names of volcanoes: A, Aso; K, Kuju; T, Tsurumi; U, Unzen; Y, Yufu. The blue letters indicate the names of prefectures: FU, Fukuoka; KA, Kagoshima; KU, Kumamoto; MI, Miyazaki; NA, Nagasaki; OI, Oita; SA, Saga