JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-SS Seismology

[S-SS15] [JJ] Strong Ground Motion and Earthquake Disaster

Wed. May 24, 2017 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL7)

[SSS15-P24] Density Structure Model Estimated from Gravity Survey around Mashiki damaged by 2016 Kumamoto Earthquake

Shun Araki2, Tatsuya Noguchi3, Masao Komazawa4, Shoya Arimura3, Mitsuhiro Tamura3, Kei Nakayama3, *Hitoshi Morikawa1, Takashi Miyamoto5, Kahori Iiyama1, Yoshiya Hata6, Masayuki Yoshimi7, Takao Kagawa3, Hiroyuki Goto8 (1.Department of Urban Design and Built Environemt, Tokyo Institute of Technology, 2.Department of Civil and Environmental Engineering, Tokyo Institute of Technology, 3.Department of Management Social Systems and Civil Engineering, Tottori University, 4.Oyo Corporation, 5.Department of Civil Engineering, Yamanashi Univsersity, 6.Division of Global Architecture, Osaka University, 7.Geological Survey of Japan, AIST, 8.Disaster Prevention Research Institute, Kyoto University)

Keywords:Gravity Survey, Mashiki, Kumamoto, Japan, Density Structure

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.