Seismic Expedition in the Hinagu Fault Area, Kyushu Island, Japan

The Hinagu fault system, Kyushu, Japan, is located in the westernmost part of the Beppu-Shimabara graben. This fault system is characterized by a quite high seismic activity and estimated to have a higher seismic risk among active faults in Kyushu Island. In 2003, we conducted an extensive seismic expedition in and around the Hinagu fault area. This expedition involves seismic refraction/wide-angle reflection experiment using dynamite shots and seismic array observation both for the active and passive seismic sources. For the refraction/wide-angle reflection study, two profile lines of 56.4 and 32.1km lengths were set in EW and NNE-SSW directions, respectively, on which 7 dynamite shots of 100－200kg charge and 359 recorders were deployed. The array observations, which were designed for high-resolution imaging of crustal scatterors and reflectors, were undertaken at 5 sites in the fault region. This paper presents the outline of this seismic expedition and fundamental data obtained