Paper No. 59-6
OKUNO, Mitsuru, Department of Earth System Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku,, Fukuoka, 814-0180, Japan, TORII, Masayuki, Implementation Research and Education System Center for Reducing Disaster Risk, Kumamoto University, 2-39-1 Kurokami, Chuo-ku,, Kumamoto, 860-8555, Japan, NISHIYAMA, Ken-ichi, Graduate School of Science & Technology, Tokushima University, 2-24, Shinkura-cho,, Tokushima, 770-8501, Japan, NAKANISHI, Toshimichi, AIG Collaborative Research Institute for International Study on Eruptive History and Informatics, Fukuoka University, 8-18-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan, YOKOTA, Shuichiro, Interdisciplinary Faculty of Science and Engineering, Shimane University, 1060 Nishikawatsu-cho, Matsue, 690-8504, Japan and YAMAMOTO, Shigeo, Slope Disaster Working Group, JSEG Kyushu Branch, C/O 6-3-27 Torigai, Jonan-ku, Chuo Kaihatsu Co., Fukuoka, 814-0103, Japan, okuno@fukuoka-u.ac.jp
The 2016 Kumamoto earthquake is a series of earthquakes that includes a Mw 7.0 main shock that struck at 01:25 JST on April 16, 2016 beneath Kumamoto City in Kyushu Island, SW Japan, at a depth of about 10 km. One of the foreshock earthquakes had a Mw 6.2 at 21:26 JST on April 14, 2016 and occurred at a depth of about 11 km. The two earthquakes killed at least 49 people and injured about 3000 others in total.
The main shock triggered more than 100 collapses of loam deposits that cover the post-caldera volcanoes of Aso caldera. The loam deposits contain soil, weathered ash and noticeable tephra layers such as the Aso-Kusasenrigahama pumice (30 cal kBP) and the Aira Tn ash (29 cal kBP). This is the first report of the occurrence and distribution of earthflow deposits. A geomorphological map of the Takanohane volcano area shows that earthflow deposits can be categorized into a few units, we infer these units represent sector collapses that occurred multiple times during the shaking.
Nearby, related earthflow deposits flowed relatively long distances down and along the San’oudanigawa River. At Ko-eboshi volcano, slope collapse occurred over a wide area. A large number of loam blocks from slope rushed down valley to the volcano’s foot and were able to travel long distances without water saturation. These traveling and depositional modes are similar to the effects of a debris avalanche.
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