Seismic Studies on the Crustal Structure in Wakayama District

Abstract

The crustal structure in Wakayama District was derived from close observations of local and near earthquakes at network stations spread over the area. Laboratory experiment on bed rocks was also made to get reference data on seismic velocities.
The propagation velocities of the P- and S-waves and the layer thickness obtained, are: V_p=4.3km/sec, V_s=2.4km/sec, h₁=4km for the sedimentary layer, V_p=5.5km/sec, V_s=3.2km/sec, h₂=7km for the granitic layer, V_p=6.1km/sec, V_s=3.5km/sec, h₃=15km for the basaltic layer, and V_p=8.0km/sec, V_s=4.5km/sec for the mantle surface, respectively. The crustal depth to the Mohorovicic discontinuity in this region is estimated to be about 26km.
The spatial distribution of foci of micro-earthquakes in the northern part of the district, is confined above the granitic layer.