Crustal deformation model of the Beppu‑Shimabara graben area, central Kyushu, Japan, based on inversion of three-component GNSS data in 2000–2010

The 2016 Kumamoto earthquakes, including an Mw-7 right-lateral earthquake on April 15 (UTC), occurred along faults within the Beppu‑Shimabara graben in central Kyushu, Japan. Previous studies showed that the graben area was under heterogeneous stress conditions with north–south T-axes and spreading in a north–south direction. Here, we construct a detailed crustal deformation model using three-component Global Navigation Satellite System data in 2000–2010 and considering the distribution of geological fault traces in this area. Our inversion analysis suggests that the strain accumulation rate for the right-lateral seismic slip segment (corresponding to the Futagawa fault), where the largest of the 2016 Kumamoto earthquakes ruptured, was several times smaller than the other segments in the Beppu‑Shimabara graben. Furthermore, we observe distinct subsidence along the Beppu‑Shimabara graben. Our base model attributes the subsidence to deflation of magma reservoirs beneath volcanoes, but the observed vertical velocities are poorly fit. In order to improve the fitting results for the vertical deformation, we need more sophisticated volcano-deformation model (such as a sill-like deformation source for Mt. Aso) or graben model. Graphical Abstract. .