著者

遠田 晋次 宮腰 勝義 井上 大栄 楠 建一郎 鈴木 浩一

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.48, no.1, pp.57-70, 1995-05-25 (Released:2010-03-11)

参考文献数

15

被引用文献数

1 2

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The Yamasaki fault system is located from the eastern Okayama to Hyogo Prefectures, southwest Japan, trending in NW-SE direction with a length of 87 kilometers. Earthquake risk evaluation of this fault system is not complete because the past seismic events have not been determined throughout the fault system. This paper reports a comprehensive survey of the Ohara fault, located at the northwestern end of the fault system. High resolution electrical exploration and five drillings at Ohara Town clearly identified the location of the fault underneath the sediment cover. Trench survey was then carried out to determine the past seismic events along the Ohara fault. The following conclusions were derived from these studies. (1) The Ohara fault shows up as a sharp resistivity contrast in the high resolution electrical exploration, reflecting mainly the difference in resistivity between acid tuff and black slate that constitute the northern and southern sides of the fault, respectively. (2) The trench observation in the log and radiocarbon dating of sediments revealed that the latest fault movement along the Ohara fault occurred between 150 and 1200 years B. P. The Harima Earthquake of 868 years AD is most likely to correspond to this fault movement. The timing of the event roughly coincides with the latest event of the Yasutomi fault (Okada et al., 1987) comprising the central part of the Yamasaki fault system. This strongly suggests that the Ohara and Yasutomi faults ruptured simultaneously or as a sequence of events during the Harima Earthquake. (3) The penultimate movement of the Ohara fault was estimated between 1500 and 3000 years B. P. If the latest event corresponds to the Harima Earthquake, then the interval between the last two events is estimated to be 400 to 1900 years. (4) The present trench survey revealed possibly four events along the Ohara fault during the Holocene. Thus the recurrence interval may be about 2500 years. Comparing this result with the interval between the last two events, movement of this fault system is likely to be aperiodic.

著者

三浦 大助 幡谷 竜太 宮腰 勝義 井上 大榮 小俣 雅志 佐々木 俊法 川崎 泰照 佐藤 賢 宮脇 明子 田中 竹延 宮脇 理一郎

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.110, no.5, pp.255-270, 2004 (Released:2005-01-07)

参考文献数

49

被引用文献数

3 2

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糸—静線活断層系南部の白州断層の活動履歴を再検討した. 白州断層南部には, 北西—南東方向に連続する2列の断層崖 (東・西断層崖) が分布し, 西側の断層上のトレンチ調査結果から2回の古地震イベントが明らかとなった. これらは1695~2720 cal y BPおよび7325~8360 cal y BPの間と考えられ, 後者は東側の断層上の最新地震イベント発生時期と近い. トレンチ調査による西側断層の活動間隔は約5000年, 鉛直の平均変位速度は0.4-0.6(-0.7) mm/yrである. 白州断層全体の鉛直の平均変位速度はイベント間で0.4-0.8 mm/yr, 周辺の変形を含めると1.0-1.8 mm/yrとなり, 少なくとも1.0 mm/yrのネットスリップ速度を持つ可能性が高い. トレンチの断層産状は横ずれ成分を含む斜めすべりを示すフラワー状構造であり, 従来の見解である西傾斜の衝上断層と区別できる.

著者

加藤 研一 宮腰 勝義 武村 雅之 井上 大榮 上田 圭一 壇 一男

出版者

JAPAN ASSOCIATION FOR EARTHQUAKE ENGINEERING

雑誌

日本地震工学会論文集 (ISSN:18846246)

巻号頁・発行日

vol.4, no.4, pp.46-86, 2004 (Released:2010-08-12)

参考文献数

125

被引用文献数

3 8

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内陸地殻内で発生する地震を対象として、既存の活断層図等の文献による調査、空中写真判読によるリニアメント調査、現地における地表踏査等の詳細な地質学的調査によっても、震源位置と地震規模を前もって特定できない地震を「震源を事前に特定できない地震」と定義し、その地震動レベルを震源近傍の硬質地盤上の強震記録を用いて設定した。検討対象は、日本およびカリフォルニアで発生した計41 の内陸地殻内地震である。地質学的調査による地震の分類を行い、9 地震12 地点の計15 記録 (30 水平成分) の強震記録を、震源を事前に特定できない地震の上限レベルの検討に用いた。Vs=700m/s 相当の岩盤上における水平方向の地震動の上限レベルとして、最大加速度値450 cm/s/s、加速度応答値1200cm/s/s、速度応答値100 cm/s が得られた。

著者

三浦 大助 幡谷 竜太 阿部 信太郎 宮腰 勝義 井上 大榮 二階堂 学 橘 徹 高瀬 信一

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.55, no.1, pp.33-45, 2002-07-25 (Released:2010-03-11)

参考文献数

26

被引用文献数

3

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Co-seismic faulting activity during the last three hundred thousands years of the Ichinose fault group, in the southern part of the 150km long Itoigawa-Shizuoka Tectonic Line active fault system, central Japan, was appraised. The Ichinose fault group consists of the mainly two distinct arcuate reverse fault traces bulged toward the east (frontal) and west (behind) directions. We conducted a trench excavation at the Nakano site across the behind fault, where the detailed geological and chronological information for the last ten thousands years was absent. The excavation resulted in evidences for the latest, at least two surface-rupturing events. The events were present sometimes between 665 and 1275 cal.y.B.P. and between 3355 and 4810 cal.y.B.P. The timing of the penultimate event is coincident with the previously estimated latest event on the frontal fault (3, 990-6, 270 cal.y.B.P.). The recurrence time and slip rate between these two events is approximately estimated as 3, 200 years and 0.9-1.8mm/yr in dip-slip, respectively. In comparison with a slip rate estimated from the geomorphological characteristics, the dip-slip rate from our excavation result is coincident well.A reappraisal of geomorphological reference deposits and a result of the seismic investigation study suggest that the total deformation rate of the Ichinose fault group is 3.5-3.7mm/yr (possibly up to 5.0mm/yr) and it becomes to increase in recent several ten thousands years. While the deformation rate suggests that the co-seismic faulting activity at the Ichinose fault group as a whole is ranked as the one of most active faults in Japan, however, it is smaller than that of 6.3-8.3mm/yr estimated previously from the gravimetric and numerical analyses.

著者

遠田 晋次 三浦 大助 宮腰 勝義 井上 大栄

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.52, no.4, pp.445-468, 2000-03-25 (Released:2010-03-11)

参考文献数

39

被引用文献数

1 3

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The Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan is a complex 150km-long fault system consisting of north-trending east-dipping reverse, northwest-trending left-lateral strike-slip, and north-trending west-dipping reverse faults. To help to resolve segmentation and to estimate the magnitude of future shocks on the ISTL, we conducted four trench excavations across the Hakushu fault, the Shimotsuburai fault, and the Ichinose fault group in the southern part of the ISTL, where no paleoseismological data for the surface faulting had been available. On the trench walls at the Hakushu fault, we found the evidence for the most recent surface-rupturing event occurring sometime between 6, 650 and 7, 000cal. y. B. P. (BC 4700-BC 5050) with approximately one meter of coseismic slip. On the Shimotsuburai fault, we exposed evidence for three events at two trench sites. The low-angle thrust faults and associated sediments record the most recent and the penultimate events occurring between 1, 370 and 2, 500cal. y. B. P. (AD 580-BC 550), and between 7, 940 and 8, 430cal. y. B. P. (BC 5990-BC 6480), respectively. Vertically offset terrace gravels indicate the dip-slip rate of the Shimotsuburai fault to be about 0.5mm/yr during the past 22, 000 years. We also found evidence for the most recent two surface-faulting events on the scarp of the frontal fault of the Ichinose fault group. The most recent event, which accompanied a coseismic slip of 1.8-2.2m, is inferred to have occurred sometime between 3, 990 and 6, 270cal. y. B. P. (BC 2040-BC 4320). The penultimate event, which appears to have a coseismic slip of 2.1-3.0m, is constrained to have occurred between 9, 520cal. y. B. P. (BC 7570) and 10, 930y. B. P. The recurrence time and slip rate are roughly estimated as 5, 000 years and 0.5mm/yr, respectively. Regarding the long elapsed time since the most recent events, the Hakushu fault and the Ichinose fault group have accumulated enough strain to produce surface-rupturing earthquakes today. Based on such long recurrence times and lower slip rates on the southern ISTL relative to the central ISTL, we suggest that multiple segment ruptures of the central and southern ISTL are unlikely to have occurred during the past 10, 000years. However, partial synchronization of rupture timings for the central and southern ISTL might have occurred around 7, 000y. B. P. though. To evaluate the fault activity in the southern ISTL more precisely and to consider fault interaction with central ISTL, we still need to investigate other fault strands of the southern ISTL, and to gather more paleoseismic evidence.