Seismic Refraction Survey in the central part of Japan

A seismic refraction experiments was conducted on November 17 and 18, 1988, in order to reveal the detail crustal structure beneath the Kii Peninsula, southwestern Japan. Observations were made on a line running in the north-south direction from Kawachinagano, Osaka Prefecture to Kiwa, Mie Prefecture. The line crosses major geological zones which characterize the geological features of southwestern Japan. Six shots were fired and the generated seismic waves were recorded at 86 temporary observation sites. Very prominent later arrivals, probably reflected waves from the lower crust or the upper mantle, can be recognized on the record sections. Results of 2-D forward and inverse modeling for first arrival time data suggest rather gentle structure in the upper crust. Although the profile length is only 65 km, two velocity discontinuities are found in the deep part of crust from reflected waves.