Estimation of S-wave velocity structures using seismic interferometry from long time series of microtremors in Suruga bay area, Japan

Nankai-Suruga Trough in Suruga bay is a plate boundary between the Eurasian plate and the Philippine Sea plate, and the occurrence of huge earthquake is expected. The S-wave velocity structure of sedimentary layers is important to the evaluation of the earthquake. Recently, seismic interferometry is used to estimate the S-wave velocity structures in the bay areas by using long time series of microtremors obtained at the peripherally deployed stations around the bay area. We here, apply the seismic interferometry in the Suruga bay area by temporally deploying the seismometers and observing continuous microtremors. The cross-correlation functions from continuous microtremors were calculated to reconstruct the Green’s functions between the stations. The dispersion measurements using the Time-frequency analysis were made to measure the dispersion of Rayleigh-wave group velocity from the cross-correlation functions of the vertical component. The group velocity of Rayleigh-wave showed geographical variation in the area. The dispersion curves were inverted to obtain the S-wave velocity profiles down to the seismic bedrock with an S-wave velocity of 2.7 km/s in the Suruga bay area by using genetic algorism. The result showed that the depth to the seismic bedrock in Suruga bay is deep more than 3 km and it is shallow less than 1km in Izu peninsula.