HR: 1340h
AN: V33D-1493    [Abstracts]
TI: Underground structure around Unzen volcano, Shimabara Peninsula, Kyushu, Japan, inferred from gravity analysis
AU: * Inoue, N
EM: naoto@aso.vgs.kyoto-u.ac.jp
AF: Aso Volcanological Laboratory, Institution Geothermal Sciences, Graduate School of Science, Kyoto University, Choyo, Aso, Kumamoto, 869-1404 Japan
AU: Takemura, K
EM: takemura@bep.vgs.kyoto-u.ac.jp
AF: nstitution for Geothermal Sciences, Graduate School of Science, Kyoto University, Noguchibaru, Beppu, Oita, 874-0903 Japan
AB: The Unzen volcanic scientific Drilling Project (USDP) has been performed flank- and conduit drillings around the Unzen volcano in the Shimabara Peninsula, Kyushu, Japan. The results of the flank-drillings revealed the subsurface structure, geological history and physical property around the Unzen volcano in the eastern part of the Shimabara Peninsula. On the contrary, the New Energy Development Organization (NEDO) has conducted various surveys on the geothermal field research project in the western part of the Shimabara Peninsula. Based on the previous study and flank-drillings, the stratigraphy of the Unzen volcano is described as follows: Quaternary Unzen volcanic products, Quaternary-Neogene rocks and Paleogene rocks (in descending order). The density of the Quaternary-Neogene units varies with the facies. The density of the volcanic rocks is higher than that of the pyroclastic or sedimentary rocks. It is difficult to estimate the basement of the Unzen volcanic products from the gravity analysis. The distribution of the basement configure of the Unzen volcanic products is obtained by compiling the borehole data in the Shimabara Peninsula. We attempted to estimate the surface of the Paleogene rocks on the basis of the gravity analysis. The gravity data around Unzen volcano were adopted from the gravity CD-ROM published by the Geological Survey of Japan. We constructed the density model which consisted of the basement (the Paleogene rocks), overlaying layer (the Unzen volcano products and the Neogene - Quaternary deposits) and the high density volcanic rocks revealed by previous geological and geophysical works. The underground structure model of the surface of the Paleogene rocks and the base of the Unzen volcano products was compiled. In the poster, we will present the tectonics around in the Shimabara Peninsula based on constructed underground model and compare the underground structure with the subsurface fault activity estimated by geomorphological analysis.
DE: 1219 Local gravity anomalies and crustal structure
DE: 0920 Gravity methods
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting