Abstract
Six explosions ranging from 300kg to 600kg and a quarry blast of 7.5 tons in and around the Shizuoka district were observed within distances less than 150km from the shot points for refraction surveys of the crust in this province. As the geological structures in the Shizuoka district are highly complex, the shooting and the recording had to be made in various geological formations, which gave rise to difficult conditions that all seismic rays consisted of complicated paths. Accordingly, some of the results obtained by the experiments so far made near this region were also incorporated into this study. Combination of our experiments and those made by other researchers, in spite of short distances of observation lines, enables us to propose a four layered crustal model on the uppermost mantle.
The main features of the model obtained here are as follows: (1) The east side of the Median Tectonic Line is depressed by about 5.7km and covered with thick surface layers. (2) The upper boundary of the granitic layer is expected to be upward convex beneath the western Izu Peninsula at a depth of about 2km. (3) The basaltic layer has a thickness of about 15 km. (4) The Moho is estimated as 33km deep beneath Suruga Bay.
