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ID 25453
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title alternative
Late Holocene faulting along the Kawakami fault, an active segment of the Median Tectonic Line, southwest Japan
creator
Tsutsumi, Hiroyuki
Okada, Atsumasa
Matsugi, Hiroaki
subject
中央構造線
川上断層
トレンチ調査
最新活動時期
Median Tectonic Line
Kawakami fault
paleoseismic trenching
timing of the most recent faulting
NDC
General geography. Description and travel
abstract
The Median Tectonic Line active fault zone (MTL), with slip rates as high as 5-10 mm/yr, is one of the most active inland faults in Japan. However, the seismic hazard evaluation on the MTL is hampered by insufficient paleoseismological data, mainly due to sparse distribution of trenching sites along the fault zone. We have conducted a first major paleoseismological study of the Kawakami fault, a segment of the MTL in northwestern Shikoku. The study includes aerial photograph interpretation and paleoseismic trenching. Two trenches were excavated across the Kawakami fault northeast of downtown Komatsu, Ehime Prefecture in 1997. The sediments exposed on the walls in the eastern trench are middle to late Holocene fluvial deposits ranging in texture from silt to gravel. These sediments are offset along an almost vertical, 3-m-wide fault zone. The sense of apparent displacement across the fault zone is down to the north, consistent with Holocene scarps around the trench site.

The sediments in the trench contain evidence for three episodes of surface-rupturing earthquake in the past 4000 years B.P. The most recent surface-rupturing earthquake, event A, on the Kawakami fault occurred sometime during the 7th and 19th century AD. Historical documents report extensive damage around the trench site during an earthquake in 1596, and this earthquake may be correlated to the latest faulting on the Kawakami fault. The penultimate event, event B, occurred sometime during the 1st and 10th century AD. Another earthquake, event C, occurred after the deposition of layer Ⅶ, which was radiometrically dated at about 4000 years B.P.
journal title
活断層研究
issue
Issue 19
start page
77
end page
86
date of issued
2000-03
publisher
活断層研究会
issn
0918-1024
ncid
language
jpn
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
publisher
relation url
department
Graduate School of Letters