Abstract
The crustal structure in the Kinki district of Japan has been investigated by means of Phinney's spectral-ratio method and the travel-time analysis of microearthquakes. The crustal thicknesses at KYOTO and HIKONE, which are situated on the west and east sides of Lake Biwa, respectively, are determined as about 32km and 38km, espectively, by means of the spectral-ratio method. The value of 32km at KYOTO agrees well with the crustal thickness determined by travel times of the Kurayosi explosions, so that the crust is almost horizontally layered in the northwestern Kinki district, and the Pn velocity is 7.6km/sec. The value of 7.6km/sec is similar to that derived in the inland area of northeastern Japan, and a few percent lower than those at the coastal regions of the Pacific side of southwestern Japan. On the other hand, the crustal thickness in the northeastern Kinki district is determined as 40km by analysing microearthquakes near the Moho discontinuity beneath Lake Biwa. Therefore, the Moho-offset amounting to about 8km seems to exist at the western coastal region of Lake Biwa. This structure can explain the pattern of Bouguer anomalies in the northern part of the Kinki district very well.
