著者

松田 時彦 岡田 篤正

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.7, no.4, pp.188-199, 1968-12-20 (Released:2009-08-21)

参考文献数

79

被引用文献数

12 6 13

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The term “active fault (Katsu-danso)” appeared in the 1920's in papers of some geomorphologists in Japan. It has been used for faults active in Quaternary or late Quaternary, although the usage of the word “active” and its age-limit are different by authors. At any rate, the active fault is significant in geology in that the evidence of fault movements is recorded in the topography on the fault trace which enables detail analysis of the faulting, and in that the faulting might be detectable by means of geophysical methods, and it might be closely related to the occurrence of an earthquake. Recent studies in Japan showed that an active fault moves under a regionally-stressed condition of the crust, which has persisted during recent geologic time. If so, an “active fault” could be defined as a fault which is active under the present-day stress system. Then, the origin, orientation, and variation in time and space, of the “present” stress system are to be an important and fruitful research subject on the Tertiary to Quaternary tectonic history of the Japanese Islands. Some of the recent investigation on the active fault began to focus on this line.Studies of active faults in Japan have started from two points: the geological studies of the earthquake faults by geologists and the studies of the fault topography by geomorphologists.The geological studies of the earthquake fault was commenced by Koto, B. (1894) who had observed the surface break of the Mino-Owari earthquake of 1891 along the Neo Valley fault. Since then, geologists have investigated and described more than ten earthquake faults from Japan and Formosa. Particularly through the experiences of 1927- and 1930-earthquakes, it became clear that the mode of displacement along the earthquake fault during the earthquake is the same in the sense of displacement as the mode of the long-term displacement through the geologic periods. For example, Kuno, H. (1936) found that the Tanna fault which moved a few meters left-laterally during 1930 earthquake, has accumulated left-lateral displacement ca. 1000m since the middle Pleistocene.Almost independently of the geologists'works, geomorphologists had investigated the fault topography of Japan. By these studies, it had become clear before the War II that there are many fault scarps and fault valleys in this country, which have been produced probably by Quaternary faulting. Tsujimura, T. (1932) published a distribution map of topographically-recognized faults, in which 413 fault systems were registered.Recently, the geological and geomorphological studies have been jointly performed and the movement-history of some active faults in Quaternary time are clarified quantitatively (Table 1). It is also shown that many active faults hitherto considered to have only vertical displacement are strike-slip faults accompanied by lesser dip-slip components. The Atera fault (Sugimura & Matsuda, 1965), the Atotsugawa fault (Matsuda, 1966), and the Median Tectonic line (Kaneko, S., 1966; Okada, A., 1968), which was described recently, are examples.Some features of the active strike-slip faults described from Japan may be summerized as follows:A number of active faults or fault zones are present particularly in central Japan (the Chubu, Kinki, and Shikoku districts). They are, however, less than one hundred kilometers in length and a few kilometers in total displacement of the basement rocks, except for the Median Tectonic line (and probably the Itoigawa-Shizuoka Tectonic line).There is a marked regularity in the fault systems of the central Japan between the trend of faults and the sense of the displacement: the NW-trending faults are left-lateral, whereas the NE-trending faults are right-lateral. This implies that the earth's crust of the region is under the same stress system having the maximum (compressional) principal axis of approximate east-west.

著者

石村 大輔 加藤 茂弘 岡田 篤正 竹村 恵二

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.5, pp.775-793, 2010-10-25 (Released:2011-01-21)

参考文献数

46

被引用文献数

3 4

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Episodic subsidence events at the east coast of Lake Mikata, Fukui Prefecture, suggesting fault activity in the Mikata fault zone, are recognized from two drilling cores, MK09 core (60-m long) and NEXCO core (100-m long). Detailed lithology including widespread tephra horizons is described for the MK09 core, with 18 AMS-14C dates. The radiocarbon ages and tephrochronology of the core sediments indicate the continuous sedimentary history of Lake Mikata back to about 130 ka. We recognize eight depositional units ranging in thickness from 5 to 10 m in the MK09 core, each of which shows a clear coarsening-upward sequence from clay to gravel beds. These units are also recognized in the NEXCO core drilled 50 m from the MK09 core site by the correlation of tephras and lithofacies. Analysis of sedimentary features suggests that each unit and its boundary reflect a rapid rise of lake level and subsequent progradation of alluvial fans. The mean sedimentary interval of individual units is equivalent to about 10.6 kyr, which is meaningfully shorter than astronomical cycles of climate change (∼20, 41 and ∼100 kyrs). Thus, we interpret these cyclic units to be the results of recurrent co-seismic subsidence due to Mikata fault zone activity. According to this interpretation, we could identify at least seven subsidence events besides the 1662 Kanbun Earthquake. The mean recurrence interval of these events is estimated to be about 7.7 kyr.

著者

岡田 篤正 植村 善博 東郷 正美 竹村 恵二 吉岡 敏和 堤 浩之 梅田 康弘 尾池 和夫 松井 和夫 杉森 辰次 杉山 直紀 園田 玉紀 梅田 孝行 松村 法行 山田 浩二 古澤 明

出版者

一般社団法人 日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2005, no.25, pp.93-108, 2005-06-30 (Released:2012-11-13)

参考文献数

36

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The Kameoka basin is located to the west of the Kyoto basin. On the northeast side of the basin, two faults trending the northwest to southeast direction exist along the foot and the former edge of a mountain, respectively. They compose of the Kameoka fault zone with the length of about 13km (Okada&Togo ed.,2000).To elucidate such characteristics as distribution, subsurface structure and activity of those faults, we have carried out seismic reflections (P-waves) and deep drilling surveys across the faults. Volcanic ash and pollen analysis were also performed using core samples obtained by drillings. In this paper, we report the results of these surveys, especially about the characteristics of the concealed faults related to basin formation.By these surveys, three faults were detected along the three sections by the seismic reflection crossing the eastern half of the Kameoka basin, named as Fl, F2 and F3 faults from west to east. All faults incline to the northeast to form the reverse fault type uplifting to the northeast side.The Fl fault is concealed under the alluvial plain of the Katsura River and is an active fault having remarkable displacement of vertical direction to a few hundreds of meters. An accumulation of the displacement in the vertical direction is plainly recognized on the topographical and geological sections.The F2 fault appears in the wide deformation zone on the hanging. wall of Fl fault and is thought to be a subordinate fault of the F1 fault. From the distribution, the F2 fault is corresponded to be an active fault described by Okada&Togo ed. (2000) and identified at former edge of a mountain in the Kameoka basin. In this paper, we will call the Fl fault and the F2 fault as“ the Kameoka fault within the basin”. It is surely distributed about 4.6 km from the Umaji to the Hozu settlements in the southeast direction.Of the Kawarabayashi reflection profile, one reflection layer C has vertical displacement of 65m resulted from the activity of“ the Kameoka fault within the basin”. A pure seam from core samples of the layer is confirmed as so-called Oda Volcanic ash at 420-450ka. Therefore, the average slip rate of the vertical displacement is estimated at 0.15m per thousand of years or less, during the last about 430,000 years.We also found a fault scarplet (relative height 1.5-2.5m) on a low terrace. It seems to be formed by the F2 faulting since about 20,000 years ago. Hence the faulting of“ the Kameoka fault within the basin” since the late Pleistocene is certain, and also there is a possibility of the activity in the Holocene from the existence of the reverse-inclined terrace II at Umaji.Judged from distribution, the F3 fault is corresponding to "the Kameoka fault in the foot of a mountain" described by Okada&Togo ed. (2000). There is no evidence of the F3 faulting during the late Quaternary.

著者

岡田 篤正 松田 時彦

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.101, no.1, pp.19-37, 1992-02-25 (Released:2010-10-13)

参考文献数

42

被引用文献数

11 7

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The Neodani fault to the north of Nagoya, central Japan, is a principal strand of the Nobi fault system. The fault moved primarily in a left-lateral sense during the great Nobi earthquake of 1891 (Magnitude 8.0). The maximum vertical and horizontal offsets are 6 m at Midori and 7-8 m at Naka, respectively. After reviewing previous works, we discuss new geomorphological and geological data bearing on the 1891 and earlier paleoearthquakes in the latest Quaternary: specifically we find that1) The 1891 vertical offset was about 5 m at the western slope of Terayama which is located on the northwestern extension of the well-known Midori fault scarp.2) The subsurface data show that the vertical offset of the base of the alluvial deposits beneath the Midori scarp is about same as that of the ground surface at the scarp, implying that the 1891 event was the first faulting event since the beginning of the deposition of the allu-vium. The radiocarbon date suggests that the alluvium is not older than 1, 000 years in age.3) The lower river terrace, ca. 14, 000 years old, is displaced as 14 m vertically at Terayama in Midori where about 5 m vertical displacement occurred in 1891, and a stream incising the lower terrace on the fault line at Naka offsets ca. 28 m laterally where 7-8 m lateral displacement occurred in 1891. If the fault is characterized by the repeated occurrence of earthquakes of the same size, both the 14 m vertical offset at Terayama and 28 m lateral offset at Naka may be interpreted to be the result of 3 to 4 events occurring at average intervals of about 3, 000-4, 000 years since the formation of the lower terrace. The observation also indicates that the Neodani fault, at least in the central segment including Midori and Naka, has averaged 2m per one thousand years in the left-lateral slip rate in that period.

著者

岡田 篤正

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.51, no.3, pp.131-150, 2012-06-01 (Released:2013-06-12)

参考文献数

83

被引用文献数

1 6

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中央構造線(活)断層帯の右横ずれ断層運動,変位地形,変位速度など,1970年代の調査成果について,まず紹介した.トレンチ掘削調査による活動履歴や断層構造の解明が1980年頃からはじまり,やがて1回の変位量や最新活動時期などの究明が1990年代後半頃に行われた.こうした調査で得られた成果やその手法改善について述べた.1990年代に行われた詳細活断層図,地方自治体による活断層の総合的調査,さらに反射法地震探査について概略を紹介した.各種の調査から判明してきた断層運動の性質と履歴,四国域での最新活動時期(16世紀)と関連した歴史地震,これらに関与したと思われる活断層群(六甲・淡路島断層帯や有馬-高槻断層帯)の連動的な活動を指摘した.こうした経過で得られてきた諸成果をまとめた地震調査研究推進本部地震調査委員会(2003, 2011)による大地震の長期評価も紹介し,残された課題や展望について述べた.

著者

岡田 篤正

出版者

一般社団法人 日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2011, no.35, pp.1-13, 2011-09-30 (Released:2015-12-09)

参考文献数

73

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The 1586 Tensho earthquake occurred around the western part of central Japan. The magnitude is estimated to be around 8, as large as the 1891 Nohbi earthquake, mainly based on the intensity distribution map. However, historical documents concerning the precise damage and detailed crustal deformation etc. for this event are fairly limited as the occurrence time was during the Warring State Period.The Shokawa fault zone, Atera fault zone and Yoro-Kuwana-Yokkaichi fault zone, typical leading active faults having high activity and fresh topographical expression in central Japan, have been considered to be major candidates for the active faults which produced this great earthquake. The mysterious Tensho earthquake was selected as the main theme of a symposium held in Japanese Society for Active Fault Studies 2010 Fall Meeting, and was discussed in the oral session, based on the recent various data obtained by the investigations for these fault zones after the 1995 Hyogo-ken Nanbu (Kobe) earthquake (M7.3).

著者

尾池 和夫 JO 華龍 金 性均 慶 在福 全 明純 大倉 敬宏 久家 慶子 中西 一郎 入月 俊明 秋元 和実 山路 敦 鈴木 康弘 渡辺 満久 岡田 篤正 KIM Sung-kyun JUN Myang-soon JO Wha-ryong KYUNG Jai-bok

出版者

京都大学

雑誌

国際学術研究

巻号頁・発行日

1994

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韓国南東部の梁山断層は,ほぼ北北東-南南西方向に約200kmにわたって走り,顕著な破砕帯を伴っている.この断層系において活断層変位地形を野外調査し,その主断層についてトレンチ掘削を実施した.この断層は河成段丘面群とその構成層を変位させ,東側の相対的隆起を伴う右横ずれの活断層であることを確認した(岡田ほか,1994).蔚山郡彦陽南方では,大規模な宅地開発が進められているので,その用地を利用して,主断層に伴われる地殻運動やそれ並行すると推定した副断層について多くのトレンチ調査を行った。こうした調査から,次のような事柄が判明した.彦陽南方の台地(高位面)は北東流していたかつての酌川川が形成した扇状地であり,初生的には北東へ傾いていたはずであるが,トレンチ地点付近では西方へ逆傾斜している.掘削調査の結果,高位面を構成する礫層が撓曲変形を受けていることが判明した.この高位面の撓曲による上下変位量は約5mである.いくつかの断層は認められたが,地表面まで切断するものは見当たらなかった.梁山断層の平均変位速度や高位段丘の形成時期を解明する必要があるので,梁山断層が通過する彦陽地域から太和江沿いに河成段丘面を追跡し,海成段丘面との関係を調べ,段丘面編年に関する資料を得るように努めた.それらの結果は,次のように要約される.河成段丘面はfH面群(fH1面・fH2面)・fH面群(fH1面・fM2面)・fL面群(fL1面〜fL3面)に,海成段丘面はm1面〜m3面に区分できる.海成段丘の旧汀線高度は,それぞれ53.3m・18.7m・3.4mである.fH面群やfM面群には赤色風化殻が形成されており,とくにfH面群で顕著である.fL面群の構成層は新鮮でほとんど風化していない.各河成段丘面は滑らかに蔚山湾周辺まで連続する.蔚山湾周辺では,fH2面は+10mの位置へ,fH1面は数mの位置へと連続してゆく.fL1面は下流部で沖積面下に埋没し,蔚山湾周辺での推定高度は-10mである.こうした資料からみて,fM1面が最終間氷期直前の氷期に,m2面が最終間氷期に形成された可能性が高い.fH面群はそれ以前の海面低下期に,m1面は最終間氷期以前の高海面期に形成されたと推定できる.南北〜北北西-南南東走向の蔚山断層系(延長約40km)は慶州市付近で梁山断層系に会合するが,この中央部に沿っても活断層変位地形の存在と,段丘堆積物を変位させる断層露頭が確認された.この特徴や関連現象について調べ,次のような事柄が判明した.蔚山断層系の断層線は著しく弯曲している.断層露頭表現や地形面の変形状態とから考えると,この断層の活動様式は典型的な逆断層である.第四紀後期に形成された地形面や堆積物が明瞭に変位を受けているので,蔚山断層は明らかに活断層である.この断層は高位段丘面を15m,中位段丘面を5m,上下方向へ変位させており,累積的な変位が認められる.断層崖や段丘面の変位方向からみて,東側の山地域が少なくとも第四紀の中ごろから継続的に隆起している.蔚山断層に沿って,明瞭な断層露頭が2ヶ所で観察された.末方里集落東方にある寺谷池北岸では,破砕した花崗岩が地形面を構成する礫層に,走向:ほぼ南北で,傾斜:25-30°Eの衝上面をもって接している.露頭上部では,上盤の花崗岩を被覆する礫層と砂礫層・腐植質層が急斜・逆転している.数本の断層が伴われ,幅数10cmの断層帯となっている.開谷里集落北東方の淵安川河床でも,やや風化した礫層の上に花崗岩が衝上している.末方里集落東方では,中位面を構成するシルト質層が液状化作用を受けて変形し,堆積直後の大地震発生を示唆する.その再来時間については,堆積物や地形面の年代解明を現在行っており,それらの結果を待って評価したい.こうした南北方向の逆断層性活断層の存在は,当域もほぼ東西方向の広域応力場に置かれていることを示唆する.これは北北東-南南西方向の梁山断層系が右ずれを示すこととも符号し,同じ応力場にあることを意味する.また,浦項市付近には,海成中新統が分布していることから,中新世以降の梁山断層の運動像を解明するために,地質調査を実施した.

著者

岡田 篤正

出版者

公益社団法人地盤工学会

雑誌

土と基礎 (ISSN:00413798)

巻号頁・発行日

vol.41, no.3, pp.7-12, 1993-03-01

被引用文献数

1

著者

岡田 篤正 渡辺 満久 佐藤 比呂志 全 明純 曹 華龍 金 性均 田 正秀 池 憲哲 尾池 和夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.2, pp.111-126, 1994-04-25 (Released:2010-10-13)

参考文献数

51

被引用文献数

12 39

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Many distinct lineaments have been recognized by Landsat images in Korean Peninsula. The Yangsan fault system situated in the southeastern part of Korea is especially linear, continuously traceable for a long distance (about 200km), and particularly remarkable among these lineaments. The topographic expression of the Yangsan fault system is derived from the straightly stretching fault valley with wide shattered zones in the direction of NNE-SSW. This fault system extends for about 200km from the mouth of the Nagdong River west of Busan in the south to Yeondong in the north, and geologically separates Korean Peninsula from the Japan Sea. The amount of horizontal displacement may reach 30km. It is recognized as one of the most important faults in Korean Peninsula.From the interpretations of aerial photographs, and field surveys along the central part of the Yangsan fault system, the main results are summarized as follows:1. The Yangsan fault system has repeatedly moved in the late Quaternary. The lower to higher river terrace surfaces on this system show cumulative vertical offsets.2. The vertical component is upthrown on the east side from considering the terrace offset and the distribution of the mountainous lands. This vertical movement is reverse to the topographical situation on the meso-scale.3. The fault trace is extremely straight. The fault plane is almost vertical. The shatteredzone exceeds tens of meters in width with a remarkable fault gouge.4. The longer axis of flat clasts within the gravel observed in excavated the exploratory trench showed the re-arrangement along the fault. The predominantly right-lateral movements were recognized as the elongation of clayey parts and breccias in the fault gouge.5. From these characteristics, the Yangsan fault was clarified to be active with predominantly right-lateral movement. Estimated ages of terraces and its deposits give average rates of vertical and right slip on the Yangsan fault system at about 0.02-0.03mm/y, and at least 0.05-0.1mm/y, respectively.6. The fault topography is not found on the lower and lowest terraces. As the surface of the terrace has widely been cultivated as paddy fields for long historical time, lower fault scarplets less than a few meters high might have been modified or destroyed by the human actions. Therefore, we cannot mention the existence of the younger movement on the lower and lowest terraces.

著者

岡田 篤正 安藤 雅孝 佃 為成

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.96, no.2, pp.81-97, 1987-04-25 (Released:2010-02-25)

参考文献数

35

被引用文献数

6 2

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Four trenches (Trenches A-D) were explored across the Yasutomi fault (a strand of the Yamasaki fault system) to date recent past faultings. Trench A was 3 m deep and 28 m long across the fault (Upper in Fig. 3 and Fig. 4), and the additional excavation was made down to 5 m deep (Fig. 5) from the western wall of trench A. The sizes of other tenches are similar to that of trench A. Since this site was being developed after this trenching for the building lot of a factory, many pieces of important geological evidence were gradually exposed with progress of the construction. This enabled us to make a further detailed geological and geomorphological study of the Yasutomi fault. The results are summarized as follows : 1) Yasutomi fault, which has been considered to be predominantly left-slip active one estimated from tectonic morphologies, was geologically confirmed that this had dislocated with predominantly lateral-slip component at least since a few tens of thousand years.2) Widely sheared zones appeared along the north side of the active trace do not accompany any tectonic features. Therefore, this straightly trending depressional zone is to be recognized as a fault-line valley. A new fault was originated along the southern rim of pre-existed weak zone probably since the late Quaternary.3) The valley-filling deposits are disturbed at the lower part of the trench but not at the upper part this suggests that the fault has not moved since the deposition of the upper horizon although small earthquakes have been reported to occur frequently around the fault. Sense and amount of vertical offset, drugged structure and other fault features vary laterally along this, as common in high angle strike-slip fault.4) The latest displacement occurred between late 7 th and 12 th Centuries, probably associated with the 868 Harima Earthquake (M=7.1). Two more faultings were also inferred from C-14 dates of disturbed and undisturbed strata within a deformed zone of the fault, although they are less reliable. The recurrence interval of earthquakes as large as the 868 event is estimated to be at least 1000 or possibly a few thousand years along this strand of the Yamasaki fault system.

著者

岡田 篤正 堤 浩之

出版者

一般社団法人 日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.1990, no.8, pp.31-47, 1990-09-25 (Released:2012-11-13)

参考文献数

12

著者

岡田 篤正

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.18, pp.79-108, 1980-03-30

被引用文献数

11

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中央構造線はとくに紀伊中央部以西において各種の断層地形を伴い,右ずれ変位成分が卓越した主要活断層系を形成している。この活断層運動は二重弧の形成と関連して鮮新世最末期以来始まり,更新世中期以後激化するようになった。第四紀後期の断層運動は,場所による相違はあるものの,ほぼ累進的ないし徐々に加速するような変位速度で繰返し行われてきた。第四紀後期の右ずれ平均速度は四国中部から四国東部で1,000年につき5-10m,紀伊西部および四国西部で同じく数m,他地域ではより小さい値である。垂直変位は四国中央部の石鎚断層崖で最大1,500mに達し,1,000年につき0.8mに及ぶ平均速度で同様に累進的ないし加速的に行われてきた。水平変位に隋伴したいくつかのオーダーの波曲状変形が中央構造線活断層系の両側に認められるので,垂直変位の向きと量は各地形区で大いに異なる。中央構造線活断層系に沿う,このような様式の断層運動は第四紀を通して,西北西-東南東方向の広域水平圧縮のもとで形成されてきた。

著者

岡田 篤正

出版者

Japanese Society for Active Fault Studies

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.1987, no.4, pp.71-90, 1987

著者

吉岡 敏和 苅谷 愛彦 七山 太 岡田 篤正 竹村 恵二

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.51, no.1, pp.83-97, 1998-07-03 (Released:2010-03-11)

参考文献数

19

被引用文献数

1 1

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The Hanaore fault is a right-lateral strike-slip active fault about 48km long in central Japan. We carried out comprehensive surveys including trench excavations on the Hanaore fault to evaluate the seismic risk of the highly populated area, such as Kyoto City, along this fault. Three trenches were excavated on the fault. On the exposure of the northernmost Tochudani trench, a fault cutting fluvial sediments and humic soil beds appeared. The youngest age of displaced sediments is 460±60 14C yBP, and the sediments covering the fault is 360±60 14C yBP. This faulting event may be correlated to the historical 1662 Kambun earthquake. The southernmost Imadegawa trench was excavated on the road in the urban area of Kyoto City. A thrust fault cutting humic soil with pottery fragments of the Late Jomon period (about 3, 500 years ago) was observed on the trench walls. It was difficult to detect the age of the last faulting event due to lack of younger sediments and artificial modifications of the surficial materials. However, the southern part of the fault might not move during the 1662 earthquake because the damage in this area was much less than in along the northern and middle part of the fault. The historical documents recorded that the land along the Mikata fault which is located at the north of the Hanaore fault was uplifted, and the land along the western shoreline of Lake Biwa where is the east of the Hanaore fault was subsided during the 1662 earthquake. This means that the 1662 earthquake might be a multi-segment event caused by these three faults, the Mikata fault, the northern part of the Hanaore fault, and the faults along the western shoreline of Lake Biwa.

著者

岡田 篤正

出版者

日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.1987, no.4, pp.71-90, 1987-08-20 (Released:2012-11-13)

参考文献数

84

著者

鈴木 康弘 岡田 篤正 竹村 恵二 慶 在福 金 幸隆 廣内 大助 伊藤 愛 大石 超 中村 洋介 成瀬 敏郎 北川 浩之 渡辺 満久

出版者

日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2005, no.25, pp.147-152, 2005

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The Ulsan fault extends for 50 km along the NNW-SSE direction in the southeastern part of the Korean Peninsula; this is one of the most important active faults in Korea. Its paleoseismicity has recently attracted considerable attention. With the support of KOSEF (Korean Science and Engineering Foundation), excavation studies of this fault were conducted in 1999 as a part of the Korea-Japan cooperative research at Kalgok-ri in Kyongju city. The results obtained are summarized as follows. (1) The Ulsan fault plane has an eastward dip of approximately 30 degrees and exhibits typical reverse faulting. (2) It was reactivated three times in the past 30,000 years, in particular, twice after the age of AT tephra (approximately 25,000 years BP). (3) A vertical displacement of approximately 0.8 m occurred during the fault event, and the amount of net slip along the fault plane is calculated to be 1.6 m.

著者

岡田 篤正

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.40, pp.15-30, 1992-12-15

被引用文献数

20

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右横ずれが卓越した中央構造線活断層系は全体として直線状に延び, 地形的に明瞭に連続するが, 所々には間隙, ステップ, 屈曲部, 分岐部などの不連続部がある。この分岐のうち, とくに明瞭な横「し」の字状をなす構造については重視し, 上述の特徴に加えて, 地区毎の走向・変位速度・最新活動時期・活動間隔・地震との関係 などのMTL活断層系の諸性質を再検討して, 8セグメントと1つの不活動区域に分けた。活動的なセグメントはさらに2・3に細分される部分もあるが, こうした結果を第1図と第1表に示した。徳島県でのトレンチ調査によれば, MTL活断層系の最新活動は16世紀以降の歴史時代である。それは1596(慶長1)年大地震である可能性が大きく, 少なくともVaの部分が震源断層であったらしいが, その活動範囲はまだ詳しく判明していない。他のセグメントでも, 歴史時代の別の地震を起こした可能性が大きい。

著者

山崎 晴雄 佃 栄吉 奥村 晃史 衣笠 善博 岡田 篤正 中田 高 堤 浩之 長谷川 修一

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.40, pp.129-142, 1992-12-15

被引用文献数

6

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中央構造線(MTL)は西南口本を南北に二分する主要な地質構造線である。この断層は第四紀における日本で最大級の右横ずれ活断層でもある。その活発な活動度にも拘らず, MTLに沿っては歴史地震の発生は知られていない。長期的な地震予知や災害アセスメントに有効な最近の地質時代における断層の運動史を知るため, 1988年の夏中央構造線活断層系の一部である西条市近傍の岡村断層でトレンチ発掘調査を行なった。5つの小トレンチとそれらを繋ぐ細長い溝で構成される調査トレンチでは, 更新世末から歴史時代までの5つの地層ユニットと, それらの顕著な断層変位が認められた。各ユニットの堆積時期は地層中に含まれる有機物試料の^<14>C年代と土器片の考古学的編年によって決定された。断層は2000年前〜4世紀に堆積したIIIb層を切り, 7世紀以降に堆積したIIIc層に覆われるので最終活動時期は4〜7世紀と推定された。この値は1984年に行なわれた同じ断層の発掘調査結果と一致する。また, これ以外の断層活動時期も地層の不整合や変形構造に基づいて識別された。

著者

岡田 真介 坂下 晋 今泉 俊文 岡田 篤正 中村 教博 福地 龍郎 松多 信尚 楮原 京子 戸田 茂 山口 覚 松原 由和 山本 正人 外處 仁 今井 幹浩 城森 明

出版者

社団法人 物理探査学会

雑誌

物理探査 (ISSN:09127984)

巻号頁・発行日

vol.71, pp.103-125, 2018 (Released:2018-12-28)

参考文献数

43

被引用文献数

2

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活断層の評価を行うにあたっては,断層の地下形状も重要な情報の1つである。地下数十m以深の情報は,主に物理探査の結果から得ることができる。これまでには,物理探査は横ずれ活断層にはそれほど多く適用されてこなかったが,本研究では各種の物理探査を行い,横ずれ活断層に対する物理探査の適用性について検討した。対象地域は,近畿地方北西部の花崗岩地域に分布する郷村断層帯および山田断層帯として,4つの測線において,多項目の物理探査(反射法地震探査・屈折法地震探査・CSAMT探査・重力探査)を実施した。その結果,反射法地震探査は,地表下200〜300 m程度までの地下構造を,反射面群の不連続としてよく捉えていた。しかし,活断層の変位のセンスと一致しない構造も見られ,他の物理探査の結果と比較する必要があることがわかった。屈折法地震探査は,原理的に断層の角度を限定することは難しいが,横ずれ活断層の運動による破砕の影響と考えられる低速度領域をよく捉えることができた。CSAMT探査では,深部まで連続する低比抵抗帯が認められ,地下の活断層の位置および角度をよく捉えていたが,活断層以外に起因する比抵抗構造変化も捉えていることから,他の探査との併用によって,その要因を分離することが必要である。重力探査は,反射法地震探査と同様に上下変位量の小さい横ずれ活断層に対しては適さないと考えられてきたが,測定の精度と測定点密度を高くすることにより活断層に伴う重力変化を捉えることができた。

著者

金田 平太郎 岡田 篤正

出版者

日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2002, no.21, pp.73-91, 2002-06-30 (Released:2012-11-13)

参考文献数

35

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Surface rupture with maximum right-lateral displacement of 150cm and length of about 1 lkm was observed during the 1943 Tottori earthquake of Mw: 7.0, which struck the eastern Tottori prefecture, southwest Japan. We compiled all the previous reports and papers regarding the surface rupture associated with the earthquake as precise location maps (Appendix 1) and a data table (Appendix 2). We also showed the slip distribution along the surface rupture (Fig.3).The trace of the 1943 surface rupture exhibited the large step and quite sinuous geometry compared with other strike-slip surface breaks. This observation probably means that the causative fault for Tottori earthquake is at the infant stage on its way of evolution based on the Wesnousky's fault evolution model (Wesnousky,1988). Most of the surface rupture during the earthquake occurred along the geomorphologically detectable active fault (Shikano-Yoshioka active fault system). Thus, we can recognize the possible surface faulting event around the epicentral area based on recent understanding of tectonic geomorpholgy. However, the length of the subsurface seismogenic fault is underestimated by the presently proposed method (Odagiri and Shimazaki,2000) and this sh ould lead to crucial underestimation of the seismic moment and also strong ground motions. The method to estimate the lengt h Df the seismogenic fault must be reestablished.