[S-SS28] Active faults and paleoseismology

[SSS28-P23] Borehole drillings and reanalysis of the S-wave reflection data across the Kamatoge segment of the Nishiyama fault

Masashi MUKAI¹, *Kazunori MURATA¹, Shigeo HORIKAWA¹, Hiroyuki TSUTSUMI², Toshikazu YOSHIOKA³ (1.Suncoh consultants co.,Ltd., 2.Kyoto Univ., 3.AIST)

Keywords:Nishiyama fault, borehole drillings, S-wave seismic reflection

The Nishiyama fault, northern Kyushu, run along the sea of Genkai to Toho village and Asakura city. This fault is divided to three segments, such as Oshima segment, Nishiyama sement and Kamatoge segment. In the Kamatoge segment, there are two faults: the Kamatoge-Koishihara fault, trending NW-SE and the Haki fault, trending NE-SE. The former fault is a sinistral strike-slip fault and the later fault is dextral strike-slip fault. To clarify the subsurface geometry, geological structure and the fault activity, we carried out borehole drillings and reanalysis of the high resolution S-wave seismic reflection data based on the borehole data across the Haki fault in a Haki area.
According to the stratigraphic correlation, two beds of Quaternary strata, consisted of eight beds, are existed only lowland area. We estimated that the Haki fault is run near the low cliff.
In the result of the reanalysis seismic reflection data, the geological structure around the middle of the seismic line is characterized by north-dip (to lowland area) reflection layer in more than 10m depth.