5:15 PM - 6:45 PM
[SSS11-P07] Geological structure around estimated fault scarp of Tatsutayama fault developed on the Kumamoto castle park, Kumamoto prefecture, southwest Japan.
Keywords:Tatsutayama fault, Pleistocene, Fault scarp, Drilling survey
The Tatsutayama fault is estimated to extend 14 km long from northeast to southwest, and subsiding northwest side of the fault. Geological and topographical characteristics of the fault were described by Watanabe (1984, 1987), and vertical displacement by the fault is reported by Kumamoto Prefecture (1996). However, geomorphological evidence of recent fault activity is limited to the area of western foot of Mt. Tatsutayama. Therefore, about 2.6 km reach of the Tatsutayama fault is mapped on the Active Fault Map of GSI (Kumahara et al., 2017). To evaluate and mitigate seismic hazards of the Tatsutayama fault, the extent of the fault should be properly examined based on geological evidence of past activity of the fault as well as geomorphologic evidence.
At the northern part of the Kumamoto castle park, north-facing linear scarp is developed on the plateau formed of Aso-4 pyroclastic deposit. This scarp is regarded as fault scarp by Watanabe (1984, 1987), but detailed geomorphologic features are lost because of the landform modification for castle constructions since 16th century. As a part of active fault survey, Kumamoto Prefecture (1996) conducted pair of drilling survey at this estimated fault scarp and found the elevation of Aso-4 basement at the north side of the scarp is 13.3 m lower than the south side. Kumamoto city have conducted drilling surveys for restoration of the Kumamoto castle after the 2016 Kumamoto earthquakes (Kumamoto Castle Research Center, 2019). The results of the drilling surveys suggest that the elevations of Aso-4 basement, Aso-3 basement and top of Togawa lava are cumulatively lowered at the north side of the scarp relative to the south side. The survey found lacustrine sediment of the late of middle Pleistocene which distribute below the Aso-3 deposits. If the scarp is formed by the Tatsutayama fault, the lacustrine sediment may be deformed by the past fault activity.
To elucidate the geological structure beneath the scarp of the Kumamoto castle park and determine whether the Tatsutayama fault extends to the location or not, we conducted active fault survey since 2022FY including newly drilling surveys (Ota et al.,2024a). We report a summary of the geological structure around the scarp based on our survey. The details of result of the newly obtained drilling cores are reported by another presentation (Ota et al., 2024b, this meeting).
References
Kumahara et al. (2017) 1:25,000 Active Fault Map “Kumamoto”.
Kumamoto Castle Research Center (2019) “Report of Geological survey for the Ninomaru and other areas of the Kumamoto castle.”
Kumamoto Prefecture (1996) “Report of Active fault survey of Futatagwa fault zone and Tatsutayama fault.”
Ota et al. (2024a) Annual Report on Active Fault and Paleoearthquake Researchs.
Ota et al. (2024b) JpGU2024.
Watanabe (1984) Journal of the Kumamoto Geoscience Association.
Watanabe (1987) Journal of the Kumamoto Geoscience Association.
At the northern part of the Kumamoto castle park, north-facing linear scarp is developed on the plateau formed of Aso-4 pyroclastic deposit. This scarp is regarded as fault scarp by Watanabe (1984, 1987), but detailed geomorphologic features are lost because of the landform modification for castle constructions since 16th century. As a part of active fault survey, Kumamoto Prefecture (1996) conducted pair of drilling survey at this estimated fault scarp and found the elevation of Aso-4 basement at the north side of the scarp is 13.3 m lower than the south side. Kumamoto city have conducted drilling surveys for restoration of the Kumamoto castle after the 2016 Kumamoto earthquakes (Kumamoto Castle Research Center, 2019). The results of the drilling surveys suggest that the elevations of Aso-4 basement, Aso-3 basement and top of Togawa lava are cumulatively lowered at the north side of the scarp relative to the south side. The survey found lacustrine sediment of the late of middle Pleistocene which distribute below the Aso-3 deposits. If the scarp is formed by the Tatsutayama fault, the lacustrine sediment may be deformed by the past fault activity.
To elucidate the geological structure beneath the scarp of the Kumamoto castle park and determine whether the Tatsutayama fault extends to the location or not, we conducted active fault survey since 2022FY including newly drilling surveys (Ota et al.,2024a). We report a summary of the geological structure around the scarp based on our survey. The details of result of the newly obtained drilling cores are reported by another presentation (Ota et al., 2024b, this meeting).
References
Kumahara et al. (2017) 1:25,000 Active Fault Map “Kumamoto”.
Kumamoto Castle Research Center (2019) “Report of Geological survey for the Ninomaru and other areas of the Kumamoto castle.”
Kumamoto Prefecture (1996) “Report of Active fault survey of Futatagwa fault zone and Tatsutayama fault.”
Ota et al. (2024a) Annual Report on Active Fault and Paleoearthquake Researchs.
Ota et al. (2024b) JpGU2024.
Watanabe (1984) Journal of the Kumamoto Geoscience Association.
Watanabe (1987) Journal of the Kumamoto Geoscience Association.