Paleoseismological study of the Tomogashima-suido fault, Median Tectonic Line active fault system, during the Holocene, at the eastern side of the Kitan Straits, central Japan

Authors: Futoshi Nanayama, Eikichi Tsukuda, Kiyohide Mizuno, Hisao Ishii (Osaka museum of natural history), Naoko Kitada (Geo-Research Institute) and Keiji Takemura (Kyoto Univ.)

Abstract: The Tomogashima-suido fault, a segment of the Median Tectonic Line active fault system crossing the Kitan Straits west of the Wakayama Plain, cuts the Late Pleistocene alluvial sediments and the Holocene marine sediments. We have carried out high-resolution single-channel seismic profiling and drilling to date recent faulting events.
The main results of acoustic exploration and high-resolution core analysis are as follows. (1) Several faults clearly cutting the Holocene deposits show a right-step echelon pattern. (2) Two faulting events accompanied by a layer of debris flow deposits probably triggerd by an earthquake are recognized in the Holocene deposits. (3) The last event is dated to be
around 3 ka, and penultimate event is about 8.5-9 ka. (4) Vertical displacement per event is 2 to 5.5 m. (5) Recurrence interval is 5,500 to 6,000 years, and average vertical slip rate is 0.8 to 1.0 m/ky.

Map showing submarine active faults F1 and F2, and acoustic survey lines (C1-C16) and coring sites (Site1 and Site2).

Acoustic profile of the C5 line in comparison with sedimentary columns of the Tomogashima-suido cores.

Index map