抄録
The uppermost-mantle structure in the Kinki district has been investigated using apparent velocities of subcrustal earthquakes in the Kii peninsula observed at the Tottori and Hokuriku Microearthquake Observatories. Apparent velocities determined by the least-squares method increase with depths from 7.55km/sec at 25km to 8.2km/sec at 65km in the Hokuriku network for the epicentral distances of 160-260km. They concentrate on two values, or about 7.8 and 8.0km/sec, in a depth range of 45-60km. Since no reverse profile exists, the uppermost-mantle structure has been constructed assuming a horizontally layered model. Three layers, of which velocities are about 7.6, 7.8, and 8.0km/sec, exist below the Moho. Top depths of them are 40, 50, and 60km, respectively. On the other hand, we have applied the same method to the data in the Tottori network for the epicentral distances of 130-200km. The Pn velocity has been determined as 7.6km/sec when the Moho is 32km in depth, and an about 8.0km/sec layer lies at a depth of about 60km. Therefore, the layer of about 8.0km/sec exists generally at a depth of about 60km in the Kinki district. We cannot tell, however, whether this layer is an aseismic continuation of the Philippine Sea plate or not.
