霧島火山群構造探査データの反射法処理

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An intensive refraction seismic survey was conducted in November through December 1994 around Kirishima volcanic region by a group of volcanologists from universities in Japan. About two hundred 2-Hz seismometers were deployed in the area to detect seismic signals generated by dynamites at six sites. The purpose of the experiment was to reveal velocity structure of the area through the refraction analyses. Since clear reflection phases were observed in recorded seismic signals, seismic reflection analyses were applied in this paper. However, no CDP's could be tied to the survey line due to a small number of shot and receiver locations so a simple pre-stack migration scheme was employed to locate buried reflectors in the subsurface. Although the application of conventional seismic reflection surveys were said difficult in volcanological structural surveys, our results demonstrated that clear reflection events were identified. Beneath the second shot point, which is located in the NW end of Kirishima Volcanic Chain, deep reflectors were found at about 4 km and 10 km in depth. These depths showed the coincidence with those reported by Utada et al. (1994) from VLF-MT surveys as low resistivity layers. The results of the present analysis indicated the necessity of shorter geophone spacing and the utilization of geophone arrays in the future. Moreover, the utilization of low frequency seismic waves and appropreate Jacobian in the stage of seismic migration were proposed from the comparison of the point diffractor model (Trorey, 1970; Deregowski and Brown, 1983) with a point scatterer model (Mikada, 1995).
1996-11-15

霧島火山群構造探査データの反射法処理

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