Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Oral

S (Solid Earth Sciences) » S-SS Seismology

[S-SS08] Active faults and paleoseismology

Tue. May 22, 2018 10:45 AM - 12:15 PM A07 (Tokyo Bay Makuhari Hall)

convener:Mamoru Koarai(Earth Science course, College of Science, Ibaraki University), Hisao Kondo(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Ryosuke Doke(神奈川県温泉地学研究所, 共同), Nobuhisa Matsuta(Okayama University Graduate School of Education), Chairperson:Doke Ryosuke(Hot Springs Research Institute of Kanagawa Prefecture), Azuma Takashi

11:30 AM - 11:45 AM

[SSS08-15] Generation mechanisms of large-scale fissures in Asodani area accompanied by 2016 Kumato earthquake through drilling investigation and sample analysis

*Issei Doi1, Toshitaka Kamai1, Tsuyoshi Haraguchi2, Kazuyoshi Yamada3, Naoto Ishikawa4, Takahiro Ohkura5, Hidehiko Murao6, Kenji Mima7, Mutsuki Kawashima8 (1.Disaster Prevention Research Institute, Kyoto Univ., 2.Geosciences, Osaka City University, 3.Museum of Natural and Environmental History, Shizuoka, 4.Graduate School of Human and Environmental Studies, Kyoto Univ., 5.Graduate School of Science, Kyoto Univ., 6.Murao Chiken, 7.Ohta Geo Research Co.,Ltd., 8.Japan Conservation Engineers & CO.,LTD.)

Large-scale fissures emerged in Aso-dani area accompanied with the 2016 Kumamoto earthquake. Satellite data found the regions with northern displacement on the northern side of fissures. Recent studies suggested that this was due to horizontal movement of the sediment with the thickness over 50 m but it is not sure how pore pressure supported such thick sediments.

In order to elucidate the generation mechanism of the fissures, we conducted a drilling survey in the center of one of the horizontal movement zone. As a result, the regions with northern displacement corresponded to those with thick soft sediments, and the thickness greatly changed beneath the regions with northern displacement.

X-ray photos of the cores were taken to investigate the internal structure of the sediments. They can clearly image the thin layers of sands or volcanic ash in slit-rich layers. One of the interesting features for the X-ray photos was that the dips of the thin layers changed greatly at depths of 43.5-44.5 m and 55-56 m. This suggests that the sediments deformed at these depths. We will investigate the mechanisms and ages of this deformation in the future.

Acknowledgements: Discussion with Dr. Satoshi Goto in Yamanashi University is useful. We are financially supported by collaborative research program of DPRI, Kyoto Univ. (28-U06, 29-A04).