SEGJ Technical Conference

Mapping temporal change in seismic velocity caused by the 2016 Kumamoto earthquake using cross-correlations of ambient seismic noise

Abstract Monitoring of earthquake faults and volcanoes contributes to our understanding of their dynamic mechanisms and to our ability to predict future earthquakes and volcanic activity. We report here on spatial and temporal variations of seismic velocity around the seismogenic fault of the 2016 Kumamoto earthquake (Mw7.0) based on ambient seismic noise recorded by Hi-net seismic stations. Seismic velocity near the Futagawa-Hinagu faults and Aso volcano clearly decreased during the earthquake. The velocity reduction near the faults (~0.4%) may have been due to a change in stress state or to damaged zones around the faults. Further, we mapped the post-earthquake fault-healing process. The largest seismic velocity reduction, observed at Aso volcano (~0.8%), might have been caused by pressurized volcanic fluids, but the seismic velocity at the volcano's magma body greatly increased ~3 months after the earthquake, perhaps owing to de-pressurization caused by an eruption.