3D Geometry and Slips of Offshore Active Fault based on Seismic Trenching — A Case Study on the Hinagu-Fault-Zone, Kyushu, Japan
Abstract
For comprehensive evaluation of active faults, information of both vertical and horizontal slips is necessary. However, as is often the case with offshore or blind active faults, horizontal slips tend to be difficult to identify and evaluate. As a case study to do with the difficulty, we challenged 3D-seismic trenching to reveal 3D geometry and slips on the offshore part of the Hinagu-Fault-Zone, Kyushu, Japan. The Hinagu-Fault-Zone includes sources of the 2016 Kumamoto Earthquakes (Mw 6.2 and Mw 7.0) and mainly consists of dextral faults with vertical movement. As a part of MEXT's urgent research project related to the 2016 Kumamoto Earthquakes, we conducted 3D-seismic trenching, which comprises ultra-high-resolution 3D seismic survey and offshore drilling surveys, on the offshore part of the fault zone. We obtained a seismic cube on rectangle area of 2.0 km by 1.0 km with bin size of 2.5 m by 5.0 m. The target area is 25-40 m below-sea-level, and covered by the latest Pleistocene to Holocene secession of 10-15 m thickness. We also obtained two offshore sedimentary core samples and determined depositional ages based on radiocarbon datings. Based on vertical slices of the seismic cube, we recognized that major normal fault intersects horizontal strata composed of Holocene shallow marine sediments. We interpreted the major fault have experienced at least 4 times of dip-faulting during Holocene. We revealed plan view of the faults based on time slices of the cube. The major fault steps to the right, and depression associated with minor normal faults was recognized. These observations strongly suggest that extensional duplex was formed at right-stepover section along dextral strike-slip fault. Further analysis concerned with the slip-rates are in progress and will be discussed on the presentation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP54A..06O
- Keywords:
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- 1105 Quaternary geochronology;
- GEOCHRONOLOGYDE: 1130 Geomorphological geochronology;
- GEOCHRONOLOGYDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS