著者

大竹 政和

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.95, no.3, pp.167-185, 1986-06-25 (Released:2009-11-12)

参考文献数

55

被引用文献数

1

---

The essential role of interstitial fluid pressure (pore pressure) in earthquake occurrence is strongly suggested by the observational fact that seismic activity was induced by water injection into a deep well and water impounding of an artificial reservoir. Elaborate studies related to water injection revealed following important characteristics of the induced seismicity : (1) Earthquakes are triggered to occur when the interstitial fluid pressure of the basement rock exceeds some threshold level ; (2) Focal mechanisms of induced earthquakes are in good harmony with the regional stress field ; and (3) Seismic activity propagates as far as several kilometers from the injection well. Based on those observational facts, we conclude that the injected water raising the interstitial fluid pressure releases the tectonic stress naturally accumulated. The effect of pressure change on the fracture strength of rock S is formulated in terms of the effective stress hypothesis asS=τ0+ (σn-P0) tanφwhere σn and P0 are normal stress and interstitial fluid pressure, and τ0 and φ are the coefficient of cohesive strength and internal friction angle, respectively. This criterion of rock fracture may also be applied to account for the reservoir induced seismicity. For the case of reservoir induced seismicity, however, the loading effect of water mass should be taken into consideration since some of the artificial reservoirs exhibit induced aseismicity.The effect of interstitial fluid pressure seems to be essential even for occurrence of natural earthquakes. Detailed studies on the Matsushiro earthquake swarm revealed that the earthquake swarm was brought about by the “water eruption”; high pressure water supplied at the depth beneath Matsushiro erupted to the ground surface accompanying a large number of small earthquakes which were generated by the increase of interstitial fluid pressure. Remarkable upheaval of the focal area, gushing out of large amount of water, and other associated phenomena are consistently interpreted by the water eruption model. It will be of great value for deeply understanding the nature of swarm activity to investigate whether such a mechanism is common or not to other earthquake swarms.The dilatancy-diffusion model of earthquake occurrence is briefly discussed from the viewpoint of the effect of interstitial fluid pressure. The model is a fascinating product of the effective stress hypothesis and results of laboratory experiments of rock fracture. It, however, is still dubious if the results obtained in the laboratory can directly be applied to the earthquake phenomenon occurring in the natural environment. We, therefore, emphasize the especial importance of advanced studies on induced earthquakes which occur under the half-natural and half-controlled circumstances.

著者

鶴岡 弘 大竹 政和

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.111, no.2, pp.256-267, 2002-04-25 (Released:2009-11-12)

参考文献数

34

被引用文献数

2 6

---

We conducted a numerical simulation to clarify the effects of the earth tide on earthquake occurrence. In the simulation, fault planes, having different initial stresses, are loaded by constantly increasing tectonic stress and cyclic stress due to the earth tide. Earthquakes are assumed to occur when the shear stress reached a certain threshold level. The result of the simulation indicates that the tidal effect on earthquake occurrence is strongly controlled by the ratio of stress change rate between earth tide and tectonic stress accumulation; earthquakes concentrate near phase angle 0° (maximum tidal stress) when the ratio is large, and they are distributed with a peak around-90° (maximum acceleration of tidal stress) when the ratio is small. This phase selectivity is very similar to the observations of tidetriggered earthquakes reported so far, and rock failure experiments under cyclic loading, suggesting that our approach may provide an important clue for clarifying the physical mechanism of tidal triggerings of earthquakes. Schuster's test has been widely used for detecting tidal effect on earthquake occurrence. However, it is shown by the numerical simulation that the result of a test strongly depends on the size of a data set when earthquakes have phase selectivity by nature, and that Schuster's p-value is not appropriate to represent the strength of tidal effects. Alternatively, we propose to use α, which is the amplitude of a sine curve fitted to the frequency distribution of earthquakes against phase angle, to evaluate the strength of tidal effects. We also emphasize that the effect of ocean loading is an important component of the earth tide, and cannot be neglected in a study of tidal triggerings of earthquakes.

著者

大竹 政和

出版者

独立行政法人防災科学技術研究所

雑誌

防災科学技術 (ISSN:04541871)

巻号頁・発行日

vol.41, pp.1-7, 1980-11-25

被引用文献数

1

---

関東・東海地域はアジア・太平洋・フィリピン海の各プレートが会合する場所に当たり,3つのプレートの入り組んだ相互作用によって,そのテクトニクスはきわめて複雑な状況を呈している.そのために,地震の発生メカニズムについても不明の点があまりにも多い.しかし,わが国の心臓部を擁しかつ常に大地震の危険にさらされている地域であるだけに,この複雑な場の基本的な構造を解明することば,地震予知研究の立場から見ても第一級の研究課題と言わねばならない.幸い,深層地殻活動観測施設をはじめとする地震観測網の整備が進むに従って,この地域の震源決定精度が格段に向上し,小さな地震の発震機構も精度よく決めることができるようになってきた.こうした良質の地震データを基礎こ,関東・東海地域のテクトニクスを統一的に説明するモデルが生み出された.この統一モデルの概要を紹介し,あわせて,モデルから予測される関東直下の地震の発生メカニズムについて論ずることにしたい.

著者

岡村 行信 倉本 真一 大竹 政和 平 朝彦 太田 陽子 石川 有三 鷺谷 威 加藤 幸弘 下川 浩一 粟田 泰夫

出版者

一般社団法人 日本地質学会

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

vol.1999, 1999

著者

寺島 敦 大竹 政和 小沢 邦雄

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.28, no.3, pp.239-267, 1975-10-10 (Released:2010-03-11)

参考文献数

10

---

Recently, it is suggested that underground water plays an important part in generating the earthquakes. Studies are made in the present paper on changes in flow rate, temperature and heat capacity of hot springs distributed in southern Izu peninsula. These changes are considered to be related closely with the change of underground water caused by the Izu-Hanto-Oki (off the Izu peninsula, Japan) Earthquake (138°48′E, 34°34′N, h: 10km, M=6.9, May 9, 1974).Both of the flow rate and temperature of these hot springs were found to be increased just after the earthquake.Increases of flow rate and heat capacity discharged in the Shimogamo spa contiguous to the epicentral area began about 5.7 years before the earthquake. This abnormality reverted just before the earthquake. This period of about 5.7 years fit the period of precursory phenomena prior to the occurrence of the earthquake M=6.9 expected by “Dilatancy Model”. Moreover, the behavior of the variation bears a close resemblance to what is expected for the behavior of underground water as precursory phenomena prior to earthquakes by “Dilatancy Model”.

著者

大竹 政和

出版者

統計数理研究所

雑誌

統計数理 (ISSN:09126112)

巻号頁・発行日

vol.45, no.1, pp.125-130, 1997

著者

大竹 政和

出版者

独立行政法人防災科学技術研究所

雑誌

防災科学技術 (ISSN:04541871)

巻号頁・発行日

vol.35, pp.10-14, 1979-09-25

---

「大規模地震対策特別措置法」の適用第1号として,静岡県を中心とする6県の合計170市町村が「地震防災対策強化地域」に指定された.中央防災会議,各県,各市町村,.国鉄・NHKなどの指定公共機関,石油化学コンビナートなどの民間の重要施設では,それぞれのレベルで地震防災計画を策定して,大地震の来襲に備えることになる.大地震がいよいよ発生すると判断された場合には,「警戒宣言」が発せられ,それぞれの計画に従って地震防災応急対策が実行に移される.警戒宣言は,気象庁長官から報告される専門的な地震予知情報にもとづいて,総理大臣の判断と責任において発せられることになっている.予知を前提とする地震対策という,世界にも前例を見ない野心的な試みがその第一歩をふみ出したわけである.今回の地域指定の標的は,言うまでもなく駿河湾から御前崎沖を震源地とする「東海大地震」である.それでは,予測される東海大地震とはどのような地震なのだろうか,これを予知するためにどのような努力が行なわれているのだろうか.本稿では,東海大地震の予知に関する現状を概観してみる.

著者

大竹政和 平朝彦 太田陽子編

出版者

東京大学出版会

巻号頁・発行日

2002

著者

鶴岡 弘 大竹 政和

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.111, no.2, pp.256-267, 2002

参考文献数

34

被引用文献数

1 6

---

We conducted a numerical simulation to clarify the effects of the earth tide on earthquake occurrence. In the simulation, fault planes, having different initial stresses, are loaded by constantly increasing tectonic stress and cyclic stress due to the earth tide. Earthquakes are assumed to occur when the shear stress reached a certain threshold level. The result of the simulation indicates that the tidal effect on earthquake occurrence is strongly controlled by the ratio of stress change rate between earth tide and tectonic stress accumulation; earthquakes concentrate near phase angle 0&deg; (maximum tidal stress) when the ratio is large, and they are distributed with a peak around-90&deg; (maximum acceleration of tidal stress) when the ratio is small. This phase selectivity is very similar to the observations of tidetriggered earthquakes reported so far, and rock failure experiments under cyclic loading, suggesting that our approach may provide an important clue for clarifying the physical mechanism of tidal triggerings of earthquakes. Schuster's test has been widely used for detecting tidal effect on earthquake occurrence. However, it is shown by the numerical simulation that the result of a test strongly depends on the size of a data set when earthquakes have phase selectivity by nature, and that Schuster's <I>p</I>-value is not appropriate to represent the strength of tidal effects. Alternatively, we propose to use &alpha;, which is the amplitude of a sine curve fitted to the frequency distribution of earthquakes against phase angle, to evaluate the strength of tidal effects. We also emphasize that the effect of ocean loading is an important component of the earth tide, and cannot be neglected in a study of tidal triggerings of earthquakes.

著者

大竹 政和

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.50, no.appendix, pp.83-99, 1998-03-31 (Released:2010-11-17)

参考文献数

77

---

This article reviews observational and theoretical studies on seismic gap and seismic quiescence from the view-point of earthquake forecast. “Seismic gap of the third kind” by Y. Ishikawa is also briefly discussed. Seismic gap, which is recognized as an unruptured segment of plate boundary and large-scale geological structure in the present seismic cycle, is a strong tool for identifying the zone of high seismic potential in the near future. However, the concept of characteristic earthquake is not always valid. We need reliable information on the duration of seismic cycle, slip distribution of past earthquakes, and seismic coupling for effectively applying the seismic gap hypothesis to earthquake forecast. Seismic quiescence has been reported prior to major seismic events of a wide magnitude range, from great earthquakes to rock fractures in the laboratory, but the physical mechanism is not yet established, Among the several hypotheses so far proposed, the stress relaxation model based on the laboratory-driven friction law is of particular interest since it theoretically predicts the formation of seismic quiescence as a natural consequence of the physical process of earthquake preparation. For checking the validity of the model, we need detailed studies on the time-space development of quiescence, and focal mechanism change in the surrounding area. In spite of some limitations described above, past studies demonstrate that a combined use of the seismic gap and seismic quiescence is expected to provide a most useful tool to forecast the occurrence of a large earthquake for the time range of a year to several decades.

著者

浜田 和郎 大竹 政和 岡田 義光 石田 瑞穂 松村 正三 山水 史生 佐藤 春夫 笠原 敬司 井元 政二郎 野口 伸一 山本 英二 鵜川 元雄 島田 誠一 堀 貞喜 関口 渉次 大久保 正 小原 一成 福山 英一 石橋 克彦 鈴木 将之

出版者

独立行政法人防災科学技術研究所

雑誌

国立防災科学技術センター年報

巻号頁・発行日

vol.62, pp.11-12, 1989-03-30

著者

浜田 和郎 大竹 政和 岡田 義光 佐藤 春夫 山水 史生 井元 政二郎 笠原 敬司 石田 瑞穂 山本 英二 野口 伸一 松村 正三 大久保 正 立川 真理子 鵜川 元雄 島田 誠一 堀 貞喜 小原 一成

出版者

独立行政法人防災科学技術研究所

雑誌

国立防災科学技術センター年報

巻号頁・発行日

vol.60, pp.10-11, 1987-11-30

著者

浜田 和郎 大竹 政和 岡田 義光 石田 瑞穂 松村 正三 山水 史生 佐藤 春夫 笠原 敬司 井元 政二郎 野口 伸一 山本 英二 鵜川 元雄 島田 誠一 堀 貞喜 立川 真理子 大久保 正 小原 一成 浜野 一彦 鈴木 将之 石橋 克彦

出版者

独立行政法人防災科学技術研究所

雑誌

国立防災科学技術センター年報

巻号頁・発行日

vol.61, pp.10-11, 1988-03-30