Drilling survey across the Sekidosan fault at Hakui City, Ishikawa Prefecture, central Japan

概要

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The Ouchigata Plain in western Hokuriku area is interpreted as a tectonic depression bounded on the north and south by northeast-trending reverse faults. The Sekidosan fault on the south displaces geomorphic surfaces of late Pleistocene to Holocene age along its entire length. However, the slip rate and history of Holocene faulting on the fault was not well constrained by previous studies. We have obtained subsurface geologic information by geoslicer and a core sampler across monoclinal scarps 4.6 m high on a Holocene alluvial surface in Hakui City, Ishikawa Prefecture. The samples obtained at 6 sites are 3.5 to 5.3 m long. Correlation of strata and radiocarbon dating show that a peat layer dated at about 6000 years BP is warped into a monocline. The vertical displacement of the top of the peat layer is estimated at 5.2 - 6.1 m, which gives a vertical slip rate of 0.8 - 1.0 mm/yr for the Sekidosan fault. This rate is more than twice greater than previous estimates, which requires a reevaluation of seismic hazards from this fault.
Japanese Society for Active Fault Studiesの論文