The Mitoke active fault system (MAFS) is about 50 km long with a NW-WNW strike in the western margin of the Tamba Mountains, and is generally characterized by an uplifting of the northeast side accompanied by a left-lateral slip. The MAFS is composed of many active faults and is one of the largest active fault system in the northern Kinki district. The Tonoda fault is situated in the central part of the MAFS and is about 15 km long. Based on a study of the fault topography, the Tonoda fault acted with an uplifting northeastern side and a left-lateral slip during the late Quaternary period. A paleoseismological study was requested due to the lack of evidence on which to base on evaluation of earthquake risk.
To clarify the age of the latest event and intervals of events of the Tonoda fault during the late Quaternary, trenches were excavated across the fault scarplet at Sekibayashi where this fault cut river terraces with a NW trend.
The results of this study can be summarized as follows:
This fault is a reverse fault with northeastern side up-thrown and fault planes dips about 80° to the north. Based on differences of geologic section and fault striation, this is accompanied by a left lateral slip.
1) The vertical displacements of depositional surfaces of Li and L2 terraces are 5 to 9m and 1.9-3m respectively, based on drilling and trenching data. This fault is characterized by a average vertical slip rate of 0.1-0.3m/1, 000 years during the late Quaternary period.
2) At trench B, three faulting events were identified since 11 ka. The latest event was dated to be 1, 950-2, 310y. B. P.(A. D. 100-B.C. 395), that is from the Middle Yayoi to Latest Jomon period. The second and third latest events were dated to be 5, 500-7, 500y. B. P, and 8, 500-10, 710y. B. P. The average reccurence interval of faulting is estimated to be about 3, 740 years. A much older faulting event from 17, 000-22, 000y. B. P. was only identified at trench A because of the poor resolution for a paleoseismicity analysis.

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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 sedimen t s 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 4000years B. P.

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中央構造線活断層系三野断層は, 徳島県三野町上野において中位段丘面上に逆向き低断層崖を伴って溝状凹地を形成しており(岡田, 1970;中田ほか, 1999), 凹地南縁の低断層崖基部でトレンチ調査を行った. トレンチ壁面の地層は上部層と下部層に区分される. 上部層は扇状地性の礫層と耕作土(1～6層)である, 最上位の1層は現在の耕作土で, 2～3層は旧耕作土(190±40 ¹⁴CyBP)であり, 4～6層が扇状地性堆積物である. 東側壁面の4層は10～13世紀, 西側壁面の4～6層は11～14世紀末に相当する¹⁴C年代を示す. また, 西側壁面の6層とこれを直接覆う4層の境から14～15世紀以降と推定される羽釜の遺物が産出している. 下部層は溝状凹地に堆積した池の堆積物であり, F4断層(東側壁面ではF1断層に切られる)を境として南北で構造が異なる. 北側の下部層(1～VII層)は北側に急傾斜しているのに対して南側の下部層(A～H層)はほぼ水平な構造を示す. 1層は鬼界アカホヤ火山灰(約BC5,200年)であり, V層はBC7,300～7,000年の¹⁴C年代を示す. 南側の下部の¹⁴CC年代である. トレンチにはF1～F5断層が分布しており, 水平成分ではこれらはいずれも右横ずれ断層である. 上下成分ではF1断層は南側隆起の逆断層であり, 　F2断層は南側隆起の正断層である. これに対して, F3, F4断層は北側隆起の逆断層であり, F5断層は傾斜がほぼ鉛直で北側隆起の断層である. F1断層は急傾斜した下部層を切断し, さらに上部層の4層を切り, 3層に覆われる. F2断層は上部層の4～6層を切るが, 上部が人工改変により削られており, 3層との関係は明らかでない. F1断層の活動時期は4層堆積以降, 3層堆積前であり, 三野断層の最新活動時期は14～15世紀以降で190±40¹⁴CyBP以前と推定される.

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