Temporal Changes in Seismic Velocity Detected by Ambient Noise Records Observed by Seafloor Seismic Network in the Nankai Trough, Japan

We used ambient noise records observed by DONET seafloor seismometer to detect temporal change of seismic velocity structure along the Nankai Trough subduction zone. Seismic interferometry, which can produce zero offset pseudo shot records by calculating auto-correlation function from ambient noise records, was used. In April 1
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2016, M6.0 Mie-oki earthquake occurred along the Nankai Trough subduction zone. We applied the seismic interferometry method to the ambient noise records observed before and after the earthquake. We also applied stretch interpolate technique to detect temporal change of seismic velocity during the significant events. Results suggest that more than 4.0% velocity changes occurred in DONET KME18 site, which is located in the vicinity of the hypocenter of the earthquake and imply a possibility for this technique to be used as seismic structure monitoring tool without any artificial seismic sources.