SEDIMENTARY THICKNESS IN THE EASTERN KANTO BASIN ESTIMATED BY ALL-PASS RECEIVER FUNCTION USING DENSE EARTHQUAKE OBSERVATIONS

摘要

The sedimentary thickness varied to several thousand meters played an important role for the long-period ground motions, which were observed in the Kanto (Tokyo) basin recently. However, exploration of sedimentary thickness is costly. Utilizing dense seismographic stations of K-NET, KiK-net and Sk-net, we studied the thickness variation by the All-pass receiver function (APRF) method. At each station, the travel-time differences between converted PS and P waves, Tps-p, were calculated from recordings with condition of clear initial P waves in a range about 100 km distance. The conversion of the Tps-p to the sedimentary thickness is a complex question since both P and S waves velocities related, as well as thickness. The conversion question was figured out by regression functions for the thickness factor H to the wave's travel-time differences between S and P waves, Ts-Tp, from deep-well VSP data. By combination of hundreds of the Tps-p results and the regression functions, we estimated the thickness of sedimentary basin beneath each station and obtained the thickness contours in the eastern Kanto basin. The results at several dozen locations were well confirmed by deep-hotspring wells and fault investigations.