Fig. 1

Index maps of studied area. Red star and black solid lines are the epicenter of the earthquake of April 16, 2016 determined by the Japan Meteorological Agency (JMA) (2016) and surface trace of active faults by AIST (2005), respectively. a Index map of the Japanese Archipelagos and Kyushu. Black rectangle indicates the area of (b). b Footprint of ALOS-2/PALSAR2-2 images used in this study superimposed on horizontal displacements of GEONET stations (orange vectors) relative to 960700 (white diamond), and epicenters determined by JMA (circles) during the period of April 10 18, 2016–April 10, 2018. Color of circles of epicenter changes according to the depth, the scale of which is shown in scale below the map. White, blue, purple and red rectangles are footprints of images of P130-F650, P131-F640, P23-F2950 and P23-F2960, respectively. Red triangles are Quaternary volcanoes, Aso, Kuju and Unzen volcanoes. White squares are the center of large cities; Ku: Kumamoto City, Oz: Ohzu Town, Y: Yatsushiro, S: Saga, O: Oita