3:00 PM - 4:00 PM
[J08-P-12] 3D seismic velocity structure beneath Kii Peninsula, southwestern Japan derived from receiver function analysis and seismic tomography
In order to investigate behavior of slab-derived fluids discharged from the Philippine Sea plate subducting beneath Kii Peninsula, southwestern Japan, we carried out seismic observations, receiver function analysis and seismic tomography. We estimated the geometry of the slab and the seismic velocity structure beneath the Kii Peninsula, and discussed the behavior of the fluids with the distribution of low velocity anomalies.
2. Receiver function (RF) analysis
We carried out linear array seismic observations in the Kii Peninsula from 2004 to 2013. We deployed seismometers along six profile lines with an average spacing of about 5 km. We applied RF analysis and obtained images of S wave velocity discontinuities. We estimated 3D configurations of the continental Moho, the slab top and the oceanic Moho from RF images for the six profile lines.
The continental Moho, the slab top and the oceanic Moho are clearly found in the RF images. A new knowledge obtained by the analysis is that the continental Moho dips upward in the southeast direction above the Philippine Sea slab.
3. Seismic tomography
We carried out the tomography with FMTOMO (Rawlinson et al., 2006). We used a velocity model with the 3D geometries of the three discontinuities derived from the RF analysis. We used 231,650 P travel times and 210,142 S travel times observed at the temporary stations in addition to permanent stations.
Results of the tomography show that low velocity anomalies (＆#62; 5 % in both P and S wave velocities and high Vp/Vs ratio ＆#62; 1.8) are located in deep low frequency events areas at 30 – 40 km depths on the Philippine Sea slab and that another strong low velocity anomaly (＆#62; 10 % in P wave velocity and low Vp/Vs ratio ＆#60; 1.6) is widely distributed in the lower crust beneath the northern Wakayama Prefecture where small to micro earthquake activity is very high in the upper crust.
We used waveform data from stations of NIED; JMA; ERI, Univ of Tokyo; Nagoya Univ and DPRI, Kyoto Univ.