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

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

吉岡 敏和

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

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おおいた豊後大野ジオパークでは,2016年4月の熊本地震の後,2017年には豊後大野市朝地町綿田地区における地すべりや,9月の台風18号による水害など,多くの自然災害に見舞われた.本ジオパーク内のサイトについても,熊本地震に伴って轟橋基部の柱状節理が崩落したほか,台風18号の際に白山渓谷の轟木橋が損壊するなど,いくつかの直接的被害があった.このような自然災害は,サイトの保全という観点からは損害をもたらすものでしかない.しかしながら,そもそも自然災害は地質現象そのものであり,本ジオパークのメインテーマである阿蘇火砕流にしても,もしそこに人類が生活していれば,壊滅的な被害をもたらした巨大災害になっていたことは間違いない.また,火砕流堆積物を谷が浸食し,滝や断崖絶壁といった景勝地が形成されたのも,度重なる洪水や斜面崩落などの積み重ねでしかない.さらに,深い谷と激流を克服しようとして造られたアーチ式石橋や,断崖を利用して彫られた磨崖仏なども,このような地質学的,地形学的現象の産物と言うことができよう.これまでの防災教育は,どちらかと言えば危険の周知や避難・備蓄の推奨などが中心で,災害発生メカニズムやその背景となる地質・地形環境についての啓発活動は,十分になされてきたとは言い難い.そのような中で,ジオパーク活動を進めることによって,住民一人一人が自分達の住む地域がどのように形成されたかに関心を持ち,住民自らによる災害の予測や災害時の的確な行動につながることが期待できる.おおいた豊後大野ジオパークでは,今後もシンポジウムや講演会などを通じて,地域の地質・地形をより深く理解するための活動を推進していきたいと考えている.

著者

吉岡 敏和 水野 清秀 榊原 信夫

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.1997, no.16, pp.87-94, 1997-08-30 (Released:2012-11-13)

参考文献数

9

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The Senzan fault is an active reverse fault directing N-S to NNE-SSW in the central Awaji Island. During the 1995 Hyogoken-nanbu earthquake, a characteristic surface break appeared along the Nojima fault located at the western side of the Awaji Island, however, no surface break had occurred along the Senzan fault. We excavated an exploratory trench on the Senzan fault to detect the age of the faulting events, and we confirmed a reverse fault making a contact between slope deposits and a granitic rock. The youngest age of the hurried soil deformed by the fault is 1161±67 AD. This means that the last faulting event of the Senzan fault occurred after the 12th Century. This event may correspond to the historical Keicho Fushimi earthquake in 1596 AD.

著者

吉岡 敏和

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.26, no.2, pp.97-109, 1987-07-31 (Released:2009-08-21)

参考文献数

32

被引用文献数

3 1

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The Kyoto Basin, which is situated in the central part of the Kinki district, is delineated by several active faults along its eastern and western rims. This paper describes the faulted terrace surfaces and the distribution of the Quaternary deposits in order to estimate the activity of the faults and the tectonic development around the Kyoto Basin. The basin formation model that explains the topographic features around the basin is also discussed. The findings are summarized as follows.The active faults along the eastern rim of the Kyoto Basin are characterized by right lateral movements, and those along the western rim by left lateral movements. These faults show younger activity in the northern part of the basin, and older activity in the southern part.The Osaka Group, Pliocene to Pleistocene in age, is distributed in and around the Kyoto Basin. Its accumulating area migrated northward during the Pleistocene. This migration is considered to be the result of a northword shift of the fault activity.The mechanism of basin formation during the Quaternary is explained by a model in which the compression between the Shigaraki Plateau block, situated east of the Kyoto Basin, and the Hokusetsu Mountains block, situated west of the basin, caused northward movement of the Tamba Mountains block and subsidence of the Kyoto Basin.

著者

佃 栄吉 粟田 泰夫 吉岡 敏和 EMRE Omer DUMAN Tamer Yigit KUSCU Ismail

出版者

一般社団法人 日本地質学会

雑誌

地質學雜誌 (ISSN:00167630)

巻号頁・発行日

vol.105, no.11, pp.XXI-XXII, 1999-11-15

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1999年8月17日の未明に発生したマグニチュード 7.4(米国地質調査所による)のイズミット(Ismit)地震は, トルコ北西部一帯に大きな被害をもたらし, 死者は1万7千人以上(10月14日現在, トルコ危機管理センターによる)に達した. この地震は北アナトリア断層の活動により引き起こされたもので, 被害の分布もおおよそそれに沿って東西に広がっている. 筆者らは9月14日より現地に入り, 地震後のトルコ鉱物資源調査開発総局(MTA)の調査結果をもとに, 陸域に出現した地震断層(約100km)の約60地点で, 断層運動による変位量を正確に計測した. 調査にあたっては最新の2万5千分の1の地形図と地震後に撮影された約1万分の1の航空写真を使用した. その結果, 今回の地震では走向, 変位量分布, 長さがそれぞれ異なる大小7つの断層が活動したこと(Fig. 2), 右ずれ変位が卓越し, その最大変位量は4. 9mであることなどが明らかになった. イズミット湾やサパンジャ(Sapanca)湖域の地震断層については今のところ情報がないが, 今後の陸域の詳細調査と併せて水域の調査を実施し, 地震断層の全体像を明らかにしたいと考えている. 結果は大縮尺の地震断層図として公表することにしている. この地震断層の詳細な記録は断層のセグメント構造に関する研究においてきわめて重要な情報となる. また, トルコにおいては将来の土地利用計画のための基礎資料として利活用されるものと期待している. ここでは今回の緊急現地調査で観察した地表地震断層の一部について紹介する.