Abstract
In the Toyama explosion in 1965, which was made in order to continue the investigation of crustal structure in Kinki and Shikoku crossing the Median Tectonic Line, three kinds of refracted waves from the granitic and basaltic layers and from the upper mantle were detected. The seismograms obtained in the Miboro explosions, which formed reverse shots to the Toyama explosion, were, therefore, reexamined to detect waves from the basaltic layer, since they had not been reported up to the present time. An affirmative result was obtained although these waves were considerably masked by intense waves from the granitic layer.
Because of small number of data, only a rough picture on the crustal structure was discussed in this paper. The superficial layer with a velocity of 5.5km/sec varies from 0 to 2km in thickness and tends to thin out towards southwest in Shikoku. The first layer with a velocity of 6.0km/sec has an average thickness of about 20km and is underlain by the basaltic layer with a velocity of 6.6km/sec. The thickness of the layer may be about 10km at the center of the profile. The upper mantle is deep to the NE direction. The derived structure is concordant not only with gravity data along the profile but also with the crustal structure of the western part of Japan derived from the Kurayoshi and the Hanabusa explosions.
