著者

廣野 哲朗 小村 健太朗 藤本 光一郎 伊藤 久男 ジェームズ モリ ジロウ 佐藤 比呂志

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.122, no.2, pp.323-342, 2013-04-25 (Released:2013-05-31)

参考文献数

111

被引用文献数

2 2

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Several fault-drilling projects have been conducted with the common aim of seeking direct access to zones of active faulting and understanding the fundamental processes governing earthquakes and fault behavior, as well as the factors that control their natural variability. Here, we review recent scientific drilling projects related to the Nojima Fault which slipped during the 1995 Hyogo-ken Nanbu Earthquake, the Chelungpu Fault which slipped during the 1999 Taiwan Chi-Chi earthquake, the San Andreas Fault Observatory at Depth, and the Nankai Trough Seismogenic Zone Experiment. We also briefly introduce the ongoing drilling research by the Geophysical Observatory at the North Anatolian Fault Zone, the Deep Fault Drilling Project at the Alpine Fault, and the Japan Trench Fast Drilling Project. One of the main findings of fault-drilling research is a better understanding of the physico-chemical processes of the primary slip zone during an earthquake, which is closely related to the mechanism of dynamic fault weakening. In the case of the Chelungpu fault, integrated research with borehole experiments, core sample analyses, and numerical simulations were performed, and the results indicate that thermal pressurization occurred during the 1999 earthquake, explaining the peculiar seismic behavior during the earthquake. These fault-drilling projects related to active faults certainly improve our knowledge and understanding of earthquakes. In addition, we discuss new technical problems related to handling core samples, identifying the latest slip zone, and overprinting by ancient earthquake events.

著者

末岡 茂 田上 高広 堤 浩之 長谷部 徳子 田村 明弘 荒井 章司 山田 隆二 松田 達生 小村 健太朗

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.1, pp.84-101, 2010-02-15 (Released:2010-05-21)

参考文献数

62

被引用文献数

9 8

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Quantitatively estimating denudation is generally difficult because it essentially involves the removal and loss of materials in situ. The denudation rate of mountainous areas in Japan has commonly been studied from the volume of sediment in a basin or catchment. Nonetheless, the availability of these methods is constrained spatially by upstream area and temporally by depositional age. In the last few decades, thermochronometric methods that evaluate thermal history using radiometric-dating methods have been used to evaluate the denudation and tectonic history of orogenic belts around the world. The advantages of thermochronometric methods are that we can calculate the denudation rate at each sampling point and that combining multiple methods and/or target minerals enables us to calculate denudation rates in multiple periods. However, thermochronometric methods have been applied to areas with extraordinarily high denudation rates in island arc areas such as Japan. Thus, the effectiveness of thermochronometric methods for estimating denudation rates in island arc areas has not been demonstrated. We applied apatite and zircon fission-track thermochronometry to granitic rock samples collected from outcrops and a borehole to estimate the tectonic history of the Rokko area, southwest Japan. Previous studies suggested that the Rokko Mountains have been uplifted by active faulting along their northern and southern margins during the Rokko movements, a Quaternary tectonic movement in the Kinki district. However, the tectonic history of the Rokko area prior to 1 Ma has not been revealed due to a lack of prevalent geologic markers. We estimated average denudation rates in various periods based on apatite and zircon FT ages and previously reported radiometric ages. We obtained denudation rates at about 0.04-0.10 mm/yr after about 30 Ma, 0.05-0.7 mm/yr during 50-30 Ma, 0.7-4.0 mm/yr during 70-50 Ma. The denudation rate after the deposition of the Kobe Group (36.9-30.4 Ma) is estimated to be in the 0.01-0.1 mm/yr order, while bedrock uplift rate after about 1 Ma is estimated to be about 0.5 mm/yr. Thus, the tectonic activity of the Rokko Mountains area prior to 1 Ma has been relatively low.

著者

小村 健太朗 池田 隆司 松田 達生

出版者

海洋出版

雑誌

号外地球 (ISSN:09169733)

巻号頁・発行日

no.46, pp.127-134, 2004

著者

山田 国見 安江 健一 岩野 英樹 山田 隆二 梅田 浩司 小村 健太朗

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.118, no.7, pp.437-448, 2012-07-15 (Released:2012-12-04)

参考文献数

46

被引用文献数

4 4

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垂直変位を伴うA級の左横ずれ活断層である阿寺断層の周辺から採取された地表・ボーリングコア試料に対してフィッション・トラック法による解析を行い,垂直変位量と活動開始時期を推定した.その結果,熱年代学に基づく約70 Ma以降の阿寺断層の垂直変位量は約1 kmであり,断層を挟んだ基盤岩や地形の高度差に基づいて推定された阿寺断層の垂直変位量と変わらないこと,また現在の破砕帯内で現在の断層に沿って20 Ma頃ないしそれ以降でおそらく第四紀以前に広い範囲で加熱があったことが明らかになった.前者は阿寺断層の約70 Ma以降の総垂直変位量が現在の活動様式による垂直変位量で説明できることを意味し,現在の変位様式の活動が第四紀初頭以降に開始したという従来の見解と整合的である.後者はこの時期には既に破砕帯が存在し,おそらく断層運動が始まっていたことを示す.したがって阿寺断層の現在の活動は,かつて存在した古阿寺断層の再活動に当たると考えられる.