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| | 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. In resource exploration, the monitoring further provides crucial information for effective and safe reservoir managements. We report here on spatial and temporal variations of seismic velocity of the whole Japanese Islands based on ambient seismic noise recorded by Hi-net seismic stations. Especially we focus on the spatio-temporal variation of seismic velocity during the 2016 Kumamoto earthquake. Seismic velocity near the Futagawa-Hinagu faults and Aso volcano clearly decreased during the earthquake. The velocity reduction near the faults may have been due to a change in stress state including pore pressure or to damaged zones around the faults. The largest seismic velocity reduction, observed at Aso volcano, 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. The velocity reduction was observed at other volcanoes and fluidized reservoirs. Therefore, the velocity changes identified through our monitoring could be used in the estimation of activities of volcanoes and faults. |
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