CRUSTAL STRUCTURE IN THE SOUTHERN KANTO-TOKAI REGION DERIVED FROM TOMOGRAPHIC METHOD FOR SEISMIC EXPLOSION SURVEY

The detailed P-wave velocity structure of the crust in the southern Ka nto-Tokai region was analyzed using the tomographic method for seismic refraction survey in this paper. A total of 332 P-wave arrival times received from 13 seismic explosion surveys were used in the analysis. The results indicate that analyses of travel-time curves are probably useful for the evaluation of inverted structures. The lateral heteroge neity of the velocity structure is obviously related to tectonics. The crust in the eastern region is thinner than that in the western regio n. The Conrad discontinuity obviously fluctuates. The granitic layer i s thinner beneath the oceanic region to the east of Oshima. The layer becomes about 16 km thick beneath Suruga Bay. The Conrad discontinuity drops nearly 17 km in depth beneath Suruga Bay, and velocity is relat ively low there. The Conrad discontinuity rises 6 km beneath MTL and i ts vicinity. The Moho discontinuity is located at a depth of around 34 km beneath the region to the west of TSTL and roughly coincides with the upper boundary of the seismic zone due to subduction of the Philip pine Sea Plate under the Eurasian Plate. It becomes shallow across the Suruga trough toward the eastern region. The discontinuity is located about 27 km in depth beneath the oceanic region east of Oshima.