The 2016 Kumamoto-Oita earthquake sequence: aftershock seismicity gap and dynamic triggering in volcanic areas.

The 2016 Kumamoto-Oita earthquake sequence involving three large events ( M ≥ 6) in the central Kyushu Island, southwest Japan, activated seismicities in two volcanic areas with unusual and puzzling spatial gaps after the largest earthquake ( M 7.0) of April 16, 2016. We attempt to reveal the seismic process during the sequence by following seismological data analyses. Our hypocenter relocation result implies that the large events ruptured different faults of a complex fault system. A slip inversion analysis of the largest event indicates a large slip in the seismicity gap (Aso gap) in the caldera of Mt. Aso, which probably released accumulated stress and resulted in little aftershock production. We identified that the largest event dynamically triggered a mid-M6 event at Yufuin (80 km northeast of the epicenter), which is consistent with existence of the 20-km long zone where seismicity was activated and surface offset was observed. These findings will help us study the contribution of the identified complexity in fault geometries and the geotherm in the volcanic areas to the revealed seismic process and consequently improve our understanding of the seismo-volcano tectonics. [ABSTRACT FROM AUTHOR]