Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS15] Active faults and paleoseismology

Wed. May 29, 2019 9:00 AM - 10:30 AM A02 (TOKYO BAY MAKUHARI HALL)

convener:Mamoru Koarai(Earth Science course, College of Science, Ibaraki University), Takashi OGAMI(National Institute of Advanced Industrial Science and Technology), Ryosuke Doke(Hot Springs Research Institute of Kanagawa Prefecture), Hisao Kondo(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Chairperson:Takashi Azuma(AIST), Mamoru KOARAI(Ibaraki University)

9:15 AM - 9:30 AM

[SSS15-05] Paleoseismological survey on the Shibetsu fault zone in the eastern part of Hokkaido, Japan

*Takashi Azuma1, Daisuke Hirouchi2, Koji Okumura3, Kaoru Taniguchi4, Masashi Omata4, Yorihide Kohriya4 (1.National Institute of Advanced Industrial Science and Technology, 2.Shinshu University, 3.Hiroshima University, 4.Pasco CORPORATION)

Keywords:active fault, paleoseismology, trenching survey, tephrochronology, the Shibetsu fault zone, Hokkaido

We conducted a paleoseimological survey on the Shibetsu fault zone in the eastern part of Hokkaido in 2018.
This fault zone has a length more than 52 km but no data was obtained about slip-rate and history of fault activeity in previous study (Hokkaido, 2004 and 2005). On a detailed topographic map with an air-borne LiDAR data, we found a new fault scarp with height of 2-5 m on fan produced the lastglacial age at Kotanuka site, and excurvated a trench (25 m in length, 8 m in width, 4 m in depth) and 4 drilling surveys (5 m in depth). We observed a high-angle fault cutting a tephra layer (Ma-l: ca.12,000 yrBP) and black soil with 40 cm on the trench wall. Based on drilling survey, the fan gravel layers, which covered with sandy sediment containing humic silt with 14C ages of 22,140-21,690 cal.BC and 20,587-20,343 cal.BC, is offset ca.3 m in vertical. We discuss the fault event and slip-rate of this fault with careful, because there are deformation of strata not only faulting but also periglacial process in the trench walls.