北上低地西縁断層帯の完新世後期の活動と内陸活断層の相互作用

Timing and displacement of the most recent faulting on the active reverse fault zone along the western margin of the Kitakami Lowland

後藤 秀昭

渡辺 満久

活断層研究

The Kitakami Lowland, running parallel to the volcanic front of Northeast Japan, is typical tectonic depression delineated by active faults. It has been difficult to evaluate the long-term seismic risk on this fault zone, because timing and displacement of the most recent faulting has been poorly constrained. The active faults are located east of and parallel to the eastward thrusting of the Neogene system onto Quaternary sedimentary fill. The most east flexure scarps(FAF3)on alluvial fan are 1-2m high, based on the topographic profiles across scarps. In order to obtain data on paleoseismic activity of this fault zone, we have carried out Geoslicer survey and dug pits on the faulting alluvial fan along topographic profiles. The strata exposed on the Geoslicer sample and pit wall are alluvial fan deposits contained within some lenses of humus. Successive humus named Hu1 dated at about 6000 years BP is parallel to the warping ground surface. The age from the most upper humus is about 2600 year BP. This age constrains the timing of most recent faulting event after 2600 year BP with 1-2m vertical displacement. It also suggests that no events occurred between 6000 and 2600 year BP along the FAF3.

変位地形

ジオスライサー調査

ピット調査

北上低地西縁断層

横手盆地東縁断層

fault geomorphology

geoslicer

pit survey

Kitakami Lowland west fault zone

Yokote basin east fault zone

地理・地誌・紀行 [ 290 ]

日本語

活断層研究会

[ISSN] 0918-1024

[NCID] AN10157356

[URI] http://topo.earth.chiba-u.jp/afr/index.htm