抄録
Lateral distribution of P-wave velocity in Kirishima volcanic region, South Kyushu, is studied assuming a model consisting of a uniform half space and a superficial layer, which is vertically uniform, but horizontally heterogeneous.
The reciprocal of velocity in the layer is expressed by a double Fourier series, and the coefficients are determined using the arrival time data observed at the stations belonging to Kirishima Volcano Observatory. Using the coefficients thus obtained P-wave velocity is synthesized, and the result is summarized as follows:
1) The velocity of the area lying NNW of Kirishima volcanic zone is low compared with the volcanic area itself.
2) Kakuto Basin, situated about 10km NNW of the volcanic area, shows specially low velocity.
3) Except in Kakuto Basin the velocity distribution seems not to be related to any of the Bouguer anomaly, surface geology, or topography.
4) Equal velocity contours run in NW-SE and NNE-SSW directions, which harmonize with the trends of fault series.
The above feature of distribution seems to reflect the inner structure successfully, and also the validity of the method of a double Fourier series for determining the velocity distribution of body waves in the layer.
