Abstract
Explosion seismic data in South Kyushu are reexamined and a model of the upper crustal structure is presented. A layer of P-wave velocity VP= 4.9km/sec is widely distributed over the profile. Below the layer, lateral variations in P-wave velocity are observed: VP=6.1km/sec in the western part of the profile, VP=5.9km/sec in the eastern part and VP=5.7km/sec in the central part. A depression of this layer is confirmed in the central part, or in the low velocity region. The depth of this layer increases abruptly by 1-2km at the west boundary of the region and decreases gradually toward the east. This layer subsides again by about 2km to the west of Miyakonojo City in the Osumi Peninsula. This is suggested by geological evidence as well. These variations in the depth of the layer can be interpreted well using gravity data.
Decreases in wave velocity are ascertainable in the region under the Sakurajima Volcano and the Aira Caldera where seismic waves are highly attenuated.
