[S-SS14] Active faults and paleoseismology

[SSS14-16] Evaluation of past multi-segment earthquakes on the Median Tectonic Line active fault zone – Vertical displacement history around the pull-apart basin –

*Hisao Kondo¹, Haruo Kimura², Hiroyuki Tsutsumi³, Hideki Kurosawa⁴ (1.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 2.CRIEPI, 3.Doshisha University, 4.Oyo Corporation)

Keywords:Active fault, Paleoseismology, MTL active fault zone, Historical earthquake

The Median Tectonic Line active fault zone (MTL) is the longest strike-slip fault system in Japan, extending from the west of Beppu Bay to the Kii Peninsula for a total length of ca. 444 km (e.g., Okada, 2020; Goto and Nakata, 1998; Earthquake Research Promotion Headquarters Earthquake Investigation Committee, 2017). We have conduct commissioned research projects on the MTL in FY2020-2022 and FY2023-2025 to improve the evaluation method of multi-segment earthquakes caused by long active fault zones. During the past project on the Itoigawa-Shizuoka Tectonic Line Zone, the frequency of past multi-segment earthquakes was estimated from the displacement history, such as past co-seismic displacement per event and precise timing of paleo-earthquakes, and a method was developed to evaluate the occurrence probability of multi-segment earthquakes based on the Poisson process (MEXT and AIST, 2020; Kondo, 2023). On the MTL, mainly on the Shikoku island active fault and paleoseismological surveys are ongoing with the aim of further improving the field survey methods for restoring the co-seismic displacement specific to strike-slip faults and the methods for identifying past multi-segment earthquakes. In this presentation, we will introduce the results of a survey conducted near the segment boundary between the Kawakami fault and the Okamura Fault, where a pull apart basin was formed due to right step of those right-lateral strike-slip faults.

Acknowledgement: This research was partly conducted under the research project "Research project on improving evaluation methods for multi-segment earthquakes produced by long active fault zones" by MEXT. We would like to express our gratitude to all involved.