[S-SS15] [JJ] 強震動・地震災害

[SSS15-P24] 2016年熊本地震による被災地における重力探査にもとづく基盤構造の推定

荒木 俊²、野口 竜也³、駒澤 正夫⁴、有村 翔也³、田村 充宏³、中山 圭³、*盛川 仁¹、宮本 崇⁵、飯山 かほり¹、秦 吉弥⁶、吉見 雅行⁷、香川 敬生³、後藤 浩之⁸ (1.東京工業大学　環境・社会理工学院　土木・環境工学系、2.東京工業大学 工学部 土木・環境工学科、3.鳥取大学大学院 工学研究科 社会基盤専攻、4.応用地質株式会社、5.山梨大学 工学部 土木環境工学科、6.大阪大学大学院 工学研究科 地球総合工学専攻、7.産業技術総合研究所、8.京都大学 防災研究所)

キーワード：重力探査、熊本県益城町、密度構造

Gravity survey has been carried out around downtown of Mashiki, Kumamoto, Japan, where is severely damaged by 2016 Kumamoto earthquake, from November 28 to December 2, 2016. We applied three LaCoste gravimeters and one Schintrex CG-3M. Closed observations were carried out at more than 300 sites around the central part of Mashiki with about 50-meter intervals. And, more than 150 sites surround the central part with 250- to 500-meter intervals. The observation sites satisfy enough density to discuss density structure shallower than 500-meter depth around central part of Mashiki. After applying some corrections to the observed data, the Bouguer anomaly is calculated under the assumed density of 2.4 g/cm³. Furthermore, gravity basement is estimated under an assumption of two layered medium with density difference of 0.5 g/cm³. As a result, a graben runs parallel to the Akitsu river and some isolated small basins are found inside of the graben. The central part of Mashiki is located immediately above of the one of such the small basins. This may suggest that the focusing phenomena of seismic rays.