Portal de Periódicos da CAPES

Seismic Reflection Survey in Kushibiki Area, Saitama Prefecture, Central Japan

1996; Seismological Society of Japan; Volume: 49; Issue: 3 Linguagem: Inglês

10.4294/zisin1948.49.3_327

2186-599X

Kazuo Yamaguchi, Naomi Kano, Toshiyuki Yokota, Takanobu Yokokura, Tsutomu Kiguchi,

Geology and Paleoclimatology Research

Seismic reflection survey was conducted in Kushibiki area, Saitama Prefecture, in the northwest part of the Kanto Plain, central Japan. The 12-kilometers long seismic line spans the northeast edge of the Kanto mountains, a major part of the Kushibiki terrace and a part of the Tone river lowland. It crosses the Hirai fault and two active faults, the Kushibiki fault and the Fukaya falut. Almost all reflectors dip homoclinically to northeast between the two active faults. The angle of dip is between 20° and 30°. The dipping reflectors are traceable from the near surface down to 1.5s in two-way time or 2km in depth, but the bottom of them is unclear. Some of them are very continuous. The dipping reflectors correspond to homoclinic sedimentary rocks of Neogene age and continuous ones probably to acidic tuff layers. All reflectors change dips at the Fukaya fault and the reflectors are almost horizontal on the northeast of the Fukaya fault. Few events are seen on the southwest of the Kushibiki fault. The survey reveals that the deep structure changes obviously both at the Fukaya fault and at the Kushibiki fault, although fault planes or large gaps of reflectors are not recognized at these faults. The survey area can be divided into several blocks bounded by these faults. The boundaries of these blocks are characterized by the change of seismic velocities at the Hirai fault, by the disappearance of reflectors at the Kushibiki fault and by the change of reflectors' dip at the Fukaya fault, respectively.