A05_P04

Holocene activity of the Tanna faults revealed by sediment core analyses and ground penetrating radar profiling, the Izu Peninsula, Japan

Kimura H ¹,  Nakanishi T², Yukawa M¹, Hosoya T³, Sung K⁴, Hong W⁵

¹Central Research Institute of Electric Power Industry, Abiko, Japan, ²Museum of Natural and Environmental History, Shizuoka, Shizuoka, Japan, ³Chuo Kaihatsu Corporation, Kawaguchi, Japan, ⁴Carbon Analysis Lab. Co., Ltd., Gyeryong-si, Republic of Korea, ⁵Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea

The active left-lateral strike-slip Tanna fault is one of the major faults of the NS-trending Kita-Izu fault zone, which ruptured during the 1930 Kita-Izu earthquake (Mjma=7.3). The fault zone is located in the Izu Peninsula, northern tip of the Izu–Bonin–Mariana arc, at about 100 km southwest from Tokyo. In order to reveal the Holocene activity on the Tanna fault, we surveyed the near-surface structure of an offset valley across the fault by radiocarbon dating of sediments obtained from arrayed four drilling cores and ground penetrating radar (GPR) profiling. The drilling sites were located across the NS-trending secondary strand that runs parallel to the northern part of the main strand of the Tanna fault approximately 50 m to the west. The GPR surveys were conducted along the arrays of the drilling sites. We interpreted several dipping horizons showing sedimentary structure on the geological cross-sections. The horizons were dated by AMS radiocarbon ages of plant fragments and organic soil samples that were measured by Carbon Analysis Laboratory (CAL) and Korea Institute of Geoscience & Mineral Resources (KIGAM). The results explained the Holocene vertical offsets associated with the oblique slip of the Tanna fault. This work was started as a research project funded by the Izu Peninsula UNESCO Global Geopark, and supported by Grants-in-Aid for Scientific Research (KAKENHI) JP15K01255 and JP18K03768 from the Japan Society for the Promotion of Science (JSPS).