著者

高橋 龍太郎 羽鳥 徳太郎

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.39, no.3, pp.561-577, 1961-12-15

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At 3 h 10m 59.1s (J.S.T.), Feb. 27, 1961, there occurred a remstrong earthquake off the south-east coast of Kyushu, Japan. According to the Japan Meteorological Agency (JMA), the magnitude of the earthquake was 7.2, depth 17km and the position of the epicenter 31°.7 N, 131°.7E. Accompanying this earthquake, a moderate tsunami was observed on the coasts of Kyushu and Shikoku.

著者

相田 勇 梶浦 欣二郎 羽鳥 徳太郎 桃井 高夫

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.42, no.4, pp.741-780, 1965-03-15

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A tsunami accompanying the Niigata Earthquake of June 16, 1964 is described on the basis of mareograms collected in the vicinity of the source area and a field survey, carriedout immediately after the earthquake by the members of the Earthquake Research Institute, along the coast of the Japan Sea from Akita to Naoetsu. The generating area of the tsunami, estimated by means of an inverse travel chart of the wave front based on the arrival time of the initial motion of the tsunami to the coastal station, is located in the sea on the continental shelf, extending about 90km in an elongated shape roughly parallel to the coast line from the northern part of Niigata Prefecture to Yamagata Prefecture.

著者

羽鳥 徳太郎 小山 盛雄

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.49, no.1/3, pp.127-142, 1971-09-30

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For the tsunamis which were generated off the Pacific coast of Japan during the last 76 years (1894-1969), the tsunami travel times observed at 12 tide stations are listed in Table 1. Features of the frequency distribution of travel time for NE Japan are different from those for SW Japan, because of the difference of the geographic characteristics of the tsunami source (Fig. 1). In the former region, a large frequency is found in the range of 30~40min, in contrast to 10~20m in the latter region. Starting from 19 tide stations indicated in Fig. 2, the inverse refraction diagrams of long waves are drawn on bathymetric charts (Figs. 3-12). Wave fronts are shown at 2min intervals. The uncertainty of the diagrams may be within ±2min for most of the regions considered.

著者

羽鳥 徳太郎

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.58, no.3, pp.723-734, 1984-01-14

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多数の検潮記録を用い,日本海中部地震による津波の波源域,規模などを調査した.波源域は水深2,000mの海域を中心に,津軽・男鹿沖間長さ140km,幅90kmと推定される.津波マグニチュードは,Δ-H曲線からm=2.5と格付けされる.日本海全域の津波伝播図を示し,伝播についての特徴を述べた.また,歴史津波を加え,日本海側でおきた津波の波源域分布を示し,波源域の配列・津波の空白域などを考察した.

著者

高橋 龍太郎 羽鳥 徳太郎

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.40, no.4, pp.873-883, 1963-03-10

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1. There are many theoretical studies on the generation of gravity waves due to an initial surface elevation or to a surface impulse. As to model experiments, however, very few studies have been made on this subject. Recent investigations of after-shocks and the propagation of tsunami waves have revealed that most of the generating area of a tsunami seems to be strongly elliptical in shape. The present experiment has been undertaken to clarify experimentally the characteristics of waves generated by a sudden dislocation of the bottom of elliptic shape. The experiment was carried out in a model basin (25m×40m×0.6m), in Chiba Prefecture, belonging to the Earthquake Research Institute. (Fig. 19). 2. The wave generator is an iron box, 94 cm × 56 cm × 4 cm in size, placed at the bottom level of the basin. It has an elliptic opening on the top covered with a rubber membrane, 2 mm thick, 90 cm × 30 cm (Fig. 20). This elliptic rubber membrane is made to swell out suddenly by compressed air as shown in Figs. 1 and 21. The wave-height gauge is of the parallel-wire type, consisting of 2 stainless steel triangular plates (Fig. 2). The sensitivity of the recorder is such that a deflection of 10mm on the record corresponds to 5.0mm in the water level change. No remarkable effect of capillarity exists in the records. The wave-heights were recorded by a 12-channel portable optical oscillograph. Eleven wave-height gauges were used, the remaining channel of the oscillograph being reserved for recording the motion of the center of the rubber membrane. The oscillograph chart was driven at a speed of either 10 or 30 mm/sec. 3. Records of waves due to the upheaval of the membrane were obtained at every foot from the center of the origin up to 4m and for a water depth of 5.0 cm and 17.3 cm. Details of experimental runs are shown in Table 1 and Fig. 5. A record in Fig. 6 shows the displacement of the center of the rubber membrane when the paper speed is 100 mm/sec. The time of the displacement was fixed at about 1/40 sec for all runs in the experiments. Figs. 7 and 8 show the final forms of the rubber membrane when expanded under certain pressures. Forms may be considered to be nearly a part of a paraboloid. 4. Figs. 22 and 23 are wave-height records for the water depths of 5.0 cm and 17.3 cm respectively. In these records, Nos. 1, 2 and 7 show wave-heights, respectively, just above the center of the origin and at the ends of the short and long axes of the elliptic rubber membrane. No. 12 is a record of the displacement of the centre of the origin. The front of a wave train is propagated roughly with the velocity √gh, except in the immediate neighbourhood of the origin, where a considerably larger velocity is observed. (Fig. 9) Wave trains have a dispersive character as shown in Fig. 11. 5. The initial surface elevation of water above the origin is about half of the displacement of the bottom itself. (Fig. 12). The ratio of the wave-heights at the ends of the long and short axes of the origin area is one-third, but for the positions distant from the origin, this ratio decreases. This result is interesting because the height ratio coincides with the length ratio of the elliptical axes (Fig. 13). The amplitude of an initial crest seems to decrease as r-0.5 and r-0.74 when the depths are 5.0cm and 17.3cm respectively (Fig. 14). Energy of the long-wave can be expressed as follows: E∝rη2L r: distance, η: wave-height, L: length of wave. Then we have EB/EA=(ηB/ηA)2 LB/LA EA, ηA and LA are energy, wave-height and wave length respectively along the long axis. EB, ηB and LB are corresponding quantities along the short axis. At the elliptic margin of the origin we have ηb/ηa = 3, Lb/La = 0.42, therefore Eb/Ea = 3.8, in the case of a water depth of 5 cm. For the distances 1m ≧ r ≧ 4m ηB/ηA = 1.8, LB/LA = 0.40, EB/EA = 1.3 Fig. 16 shows the azimuthal distribution of energy obtained by Run 8. The relation between the wave-length of the waves emitted into a certain direction and the radius of the ellipse in that direction seems to indicate that these two lengths are roughly proportional in the case of shallow water. (Fig. 17).

著者

村井 勇 金子 史朗

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.50, no.3, pp.p329-342,地図4枚, 1976-03

被引用文献数

1

著者

村井 勇 金子 史朗

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.50, no.3, pp.329-342, 1976-03-31

著者

武尾 実 三上 直也

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.65, no.3, pp.p541-569, 1990-12

被引用文献数

4

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Detailed rupture processes of six intraplate earthquakes in Japan, the 1961 Kitamino earthquake, the 1969 GifuKen-Chubu earthquake, the 1974 Izu-Hanto-Oki earthquake, the 1975 OitaKen-Chubu earthquake, the 1980 Izu-Hanto-Toho-Oki earthquake, and the 1984 NaganoKen-Seibu earthquake, are compiled and compared to each other to make clear common features of an earthquake rupture process. The rupture processes are obtained by waveform inversion using strong motion seismograms in previous studies. Five of these rupture processes are also compared with distributions of precisely determined aftershocks. Earthquakes with relatively smooth rupture propagation, such as the 1974 Izu-Hanto-Oki earthquake and the 1961 Kitamino earthquake, represent smoother slip distribution than earthquakes with relatively irregular rupture propagation, such as the 1969 GifuKen-Chubu earthquake and the 1980 Izu-Hanto-Toho-Oki earthquake. It is also recognized that aftershocks of magnitude greater than 4 do not occur in the large slip area. Most large aftershocks take place near the edge of the large slip region and in the small slip region. Aftershocks also tend to cluster near the edge of the large slip region. These results are very consistent with numerical experiments of dynamic rupture, so it is suggested that the relation between aftershocks and coseismic slip pattern obtained in this paper hold generally for earthquake rupture processes. A clear delay of rupture propagation occurs in the large slip area during the 1969 GifuKen-Chubu earthquake: on the other hand, the small slip area in the 1980 Izu-Hanto-Toho-Oki earthquake is characterized by a deceleration of rupture propagation. The large slip area in the former case is interpreted as a barrier which resisted fracturing at first and was broken with a high stress drop. In the latter case, mechanical weakness due to volcanic structure located around the source region, seems to have affected the rupture process. A similar geological condition may have affected the rupture process of the 1978 Izu-Oshima-Kinkai earthquake which occurred about 10 km south of the 1980 Izu-Hanto-Toho-Oki earthquake.日本内陸で発生した6つの地震について,詳細な破壊過程を取りまとめ,それらの相互の特徴及び余震分布との対応等を調べた.取り上げた地震は1961年北美濃地震・1969年岐阜県中部地震・1974年伊豆半島沖地震・1975年大分県中部地震・1980年伊豆半島東方沖地震及び1984年長野県西部地震である.これらの地震については,震源近くで記録された強震計記録の波形インバージョンにより,詳細な破壊過程が解明されている.

著者

茂木 清夫

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.47, no.3, pp.419-427, 1969-06

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Monthly distributions of small and large earthquakes in the Japanese region are discussed based on recent seismic data. Smaller earthquakes do not show any systematic annual variations. But large earthquakes with magnitude 7.5 and over occurred concentratively in some limited seasons and the active season is different in the two adjacent active regions. This regularity of large earthquakes in the Japanese region is confirmed by historical earthquake data. Regarding all the large earthquakes in the Northern and the Southern Hemispheres, no systematic annual variations can be concluded. This is not inconsistent with the above-mentioned regional regularity.|地震の頻度が季節変化を示すということが大森やDavison,その他の多くの人によって報告されているが,近年この問題を論じたものはほとんどみられない.この問題を論ずるには,信頼すべき資料にもとづいて,適切な解析を行うことが重要であるので,最近の高精度の地震資料によって再検討を加えることは有意義である.今回の結果によると,大森やDavisonらの指摘した規則性は認められないが,日本付近の大地震について,極めて著しい季節的集中性があることが見出された.要約すると,1.日本各地の小さい地震については,一般に,有意な季節変化は認められない.2.1920年以降のM7.5以上の大きい地震は特定の季節にのみ集中して起こる傾向がみられる.この傾向は,1600から1919までの大地震(M7.9以上)についても認められ,その集中性は統計的に有意である.その活動の季節は場所によってちがい,大きい地震は,北海道・三陸の太平洋側沖合では2月から5月まで,とくに3月に集中し,宮城県沖から関東・東南海道にかけては9月から1月まで,とくに12月に集中して起こった.3.世界中の大きい地震については,南北両半球の大きい地震がとくに夏に多いという規則性(Davisonによる)は認められない.

著者

Uyeda Seiya Watanabe Teruhiko Ozasayama Yoji Ibaragi K.

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.55, no.1, pp.55-74, 1980-08-25

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Results of terrestrial heat flow measurements in Peru and Ecuador conducted in 1969, are reported. Eight different sites in Peru and one site in Ecuador were visited for underground temperature measurement. However, data from only five metal mines in Peru and the metal exploration site in Ecuador were usable. The geothermal gradient data on four oil fields in Peru and two in Ecuador were referenced. Although high heat flow has been indicated on the continent side of the Andes (the Gasapalca and the Guajone mines and the Ucayali oil field), low geothermal gradients were also found in mines in high Andes (the Raura and Cerro Verde mines). The latter are suspected to be the result of ground water circulation. The highly disturbed cases of the Morococha and San Vicente mines showed almost zero gradient. Much more work is needed to delineate the regional heat flow pattern of the area.

著者

纐纈 一起 鷹野 澄 坪井 誠司 宮武 隆 阿部 勝征 萩原 幸男

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.64, no.4, pp.517-532, 1990-03-30

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地震予知計画の下で国立大学により運営されてきた地震予知観測情報ネットワークでは,各構成機関により維持・管理されている約160点の地震観測点の波形データが,全国7箇所の地域センター等に集められ,そこでそれぞれ独自に開発された自動処理システムにより,地震波到着時刻の読み取り・震源位置の決定などがリアルタイムで行なわれている.この処理結果はオンラインで地震研究所の地震予知観測情報センター(EPDCに転送され,リアルタイム地震データとしてデータベースに保存されている.EPDCではこのデータを統合し,TSSにより表示できるようにしたシステムを開発した.統合処理は2つのジョブが前処理と本処理を担当する.前処理ではデータを震源時順に並べ替えることと,震源時と震央座標が近い地震を同一地震と仮判定することが行なわれる.この結果がさらに本処理に送られ,親子法による同一地震の本判定と震源再決定が実行される.震源再決定で得られた統合処理結果は,ユーザのTSSごとに起動される検索プログラムで表示させることができる.1ヵ月間の処理結果を気象庁の震源速報と比較したところ,海の地震の深さが異なるのが目立つ程度で,マグニチュード3半ばより大きい地震はよく一致した.それより小さな地震では全般的に気象庁より検知能力が高いが,観測網が粗い中国・四国地方やまったく観測点がない九州地方は気象庁が優れている.本システムの今後の課題は,現在大きな地震のデータ統合を優先しているため,小さい地震の分離能力が弱い点を改善することである.また,現在情報不足で困難となっているマグニチュードの独自決定も課題であろう.

著者

大堀 道広 纐纈 一起 南 忠夫

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.65, no.2, pp.433-461, 1990-09-28

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本論文は,不整形地盤の3次元問題について,解析手法を提案し,さらにこれを用いて堆積盆地の地震動特性の検討を行ったものである.まず, 2次元問題において不整形地盤を解析するための有力な手法と評価されているAL法を, 3次元問題への拡張するための定式化を行った.従来AL法による3次元解析では特に工学的に重要な平面S波入射の垂直入射問題を取り扱うことが困難とされていた.この問題を,ベクトル・ポテンシャルによる変位の表現式を工夫することにより解決した.そして,提案した解析手法の妥当性と作成したプログラムの信頼性を確認するために,他の手法により示されている軸対称堆積盆地についての解析結果と比較したところ,良い一致を示した.続いて,これまで取り扱われることの少なかった3次元地下構造を有する堆積盆地の地震動特性を,軸対称問題ばかりでなく,非軸対称問題についてもAL法による3次元解析を行い,得られた周波数応答および時刻歴応答を1次元解析および2次元解析による応答と比較検討した.その結果, 1次元解析よりも2次元解析, 2次元解析よりも3次元解析というように,解析する次元が高くなるにつれて,堆積盆地の地表動には,より短周期の波動が励起され,振幅もより大きくなり,継続時間もより長くなるという傾向が見られた.これは, 3次元的な地下構造が地震動に与える影響が非常に大きいことを示唆している.

著者

Takeo Minoru Mikami Naoya

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.65, no.3, pp.541-569, 1990-12-25

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Detailed rupture processes of six intraplate earthquakes in Japan, the 1961 Kitamino earthquake, the 1969 GifuKen-Chubu earthquake, the 1974 Izu-Hanto-Oki earthquake, the 1975 OitaKen-Chubu earthquake, the 1980 Izu-Hanto-Toho-Oki earthquake, and the 1984 NaganoKen-Seibu earthquake, are compiled and compared to each other to make clear common features of an earthquake rupture process. The rupture processes are obtained by waveform inversion using strong motion seismograms in previous studies. Five of these rupture processes are also compared with distributions of precisely determined aftershocks. Earthquakes with relatively smooth rupture propagation, such as the 1974 Izu-Hanto-Oki earthquake and the 1961 Kitamino earthquake, represent smoother slip distribution than earthquakes with relatively irregular rupture propagation, such as the 1969 GifuKen-Chubu earthquake and the 1980 Izu-Hanto-Toho-Oki earthquake. It is also recognized that aftershocks of magnitude greater than 4 do not occur in the large slip area. Most large aftershocks take place near the edge of the large slip region and in the small slip region. Aftershocks also tend to cluster near the edge of the large slip region. These results are very consistent with numerical experiments of dynamic rupture, so it is suggested that the relation between aftershocks and coseismic slip pattern obtained in this paper hold generally for earthquake rupture processes. A clear delay of rupture propagation occurs in the large slip area during the 1969 GifuKen-Chubu earthquake: on the other hand, the small slip area in the 1980 Izu-Hanto-Toho-Oki earthquake is characterized by a deceleration of rupture propagation. The large slip area in the former case is interpreted as a barrier which resisted fracturing at first and was broken with a high stress drop. In the latter case, mechanical weakness due to volcanic structure located around the source region, seems to have affected the rupture process. A similar geological condition may have affected the rupture process of the 1978 Izu-Oshima-Kinkai earthquake which occurred about 10 km south of the 1980 Izu-Hanto-Toho-Oki earthquake.

著者

宇佐美 龍夫 浅野 潤三

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.47, no.2, pp.271-394, 1969-07-31

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A bibliography of field studies on major earthquakes in Japan was prepared. This includes papers concerning the field inspection, seismometrical study, study of related phenomena and investigation on damages which were published before the end of 1965. The list consists of the following items: (1)reference number (2)author's name (3)title of the paper (4)name, volume, year and page of Bulletin in which the paper is published or name of publishers (5)name and year of earthquake studied (6)main subject Date, name, latitude, longitude, focal depth, magnitude and reference number of earthquakes are arranged in another table. Papers are classified by the year of earthquake and main subject and arranged in a form of table.

著者

Fukao Yoshio Kono Masaru Yamamoto Akihiko Saito Matsuhiko Nawa Kazunari Giesecke Alberto Perales Crisolfo

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.74, no.2, pp.161-266, 2000-03-21

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We collected all the data of gravity measurements carried out over the last 40 years by Institute Geofisico del Peru (IGP). Because of the long time since data collection, some of the information needed for data reduction were lost over the years. This loss made it difficult for us to determine all of the gravity values unambiguously and consistently from the presently available IGP data alone. Accordingly, there was a need for independently determined gravity stations to which the measurements done by IGP may be compared. In order to provide reference gravity values, we utilized Japanese survey data collected between 1980 and 1984, and conducted more surveys in various parts of Peru in the period between 1995 and 1998. These gravity stations number more than 800, and provide three or more reference points for each of the IGP survey routes. Using these references, the gravity values were calculated for the IGP dataset and Bouguer corrections were applied. Finally, a Bouguer anomaly map of Peru was produced based on these data. This paper reports all the procedures involved in the data reduction, discusses the reliability of the reduced data, and points out the main features of the Bouguer anomaly map.

著者

溝上 恵

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.55, no.2, pp.483-504, 1980-11-15

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It has been pointed out from geological and geomorphological evidences that the time rate of undulatory crustal movement shows a remarkable dependence on its wavelength. Specific studies on the problem were made by MATSUDA (1960, 1961, 1964), KAIZUKA (1967, 1968) and OTA (1968, 1969). KAIZUKA compared the rate of folding in the Quaternary with the mode of undulatory crustal movements in the present. He indicated such regularities of folding as the smaller the wavelength, the greater the rate of folding and the rate of present folding is in the same order with that of the Quaternary folding.

著者

飯高 隆 中村 功 溝上 恵

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.64, no.1, pp.37-50, 1989-06-30

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関東地方においては,これまでに地震波速度構造の不均質性について様々な研究がなされてきた.これらの研究の結果,太平洋プレート,フィリピン海プレートの沈み込みが示された.このように複雑な構造をした地域において,沈み込むプレートの形状を求めることは,大変重要なことである.東京大学地震研究所の日立(HIT)の観測点の地震波記録で,P波とS波の間に立ち上がりのはっきりした後続波が見られた.この研究では,この後続波が,沈み込む太平洋プレート上面でPS変換された波であることを明らかにし,この変換波を用いて沈み込む太平洋プレート上面の深さを求めた.このように変換波を用いる方法は,プレート上面の深さを求めるのに有効であることが知られている.この研究において,関東地方下で求められた太平洋プレート上面は,日立の観測点下で約60kmの深さに求まり,その面は2重深発面の上面にほぼ一致した.また,この深さはS波の反射から求められた結果(小原,1987)と矛盾しない.

著者

雑賀 敦 平松 良浩 大井田 徹 山岡 耕春

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.76, no.1, pp.75-86, 2001-07-25

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Spatial and temporal variations in seismic anisotropy in the crust are investigated using earthquakes in the crust and at the upper boundary of the subducting Philippine Sea plate in the Tokai region, central Japan. We use waveform data from December 1986 to August 1999 recorded by the micro-earthquake observation network of the Research Center for Seismology and Volcanology, Nagoya University. The method of Silver and Chan (1991) is applied to evaluate splitting parameters, a leading shear-wave polarized direction and a delay between two polarized waves. A total of 362 high-quality waveform data within the incident angle of 35° are analyzed in this study. The leading shear-wave polarized directions are approximately E-W, in spite of differences of focal depths. This direction is consistent with the direction of regional horizontal maximum compressive stress in the Tokai region reported before. The time delay increases in proportion to the focal depth. These results indicate that the regional compressive stress controls anisotropy not only in the upper crust but also in the lower crust. Assuming the uniform distribution of anisotropy, the degree of anisotropy is estimated to be 0.5% in the lower crust. An increase in time delays between two-polarized waves is found before and after the Aichi-ken Tobu earthquake (M = 5.7) in 1997 at the station STN. This variation is statistically significant with the confidence level of 99.999% and is not an apparent change due to a variation in hypocenter distribution. No temporal variation of splitting parameters is found at the station INU. These results can be explained by a change of the volumetric and areal strain in the most-upper part of the crust due to the postseismic slip of the Aichi-ken Tobu earthquake.

著者

Hatori Tokutaro

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.47, no.6, pp.1063-1072, 1969-12-20

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The wave source of the tsunami generated off West Hokkaido (Shakotan Peninsula), in the Japan Sea, on Aug. 2, 1940 is estimated by means of an inverse refraction diagram, making use of a new bathymetric chart. The source area extends 170km in the NNW-SSE direction, which is smaller than that obtained by Miyabe (1941). However, the dimension estimated by the present analysis is still large for the earthquake magnitude of M=7.0. From a comparison of the geographic distribution of the earthquake intensity with those of the other tsunamigenic earthquakes that occurred in the Japan Sea, the magnitude of this earthquake is investigated. Effective tsunami height observed on the surrounding coasts of the Japan Sea can be explained by the direction of the present source. Magnitude of the tsunami of 1940 seems to be equal to that of the Niigata tsunami of 1964 and is represented as m=2. Besides, the wave source of the tsunami generated off Rumoi, West Hokkaido, on Nov. 4, 1947 is discussed, taking the aftershock area into consideration.|1940年8月2日,北海道積丹沖に起きた津波は日本海全域に伝播し,北海道西岸をはじめソ連の沿海州と北朝詳,隠岐にも家屋,船舶などに被害を与えた,地震の規模Mは,気象庁の地震カタログ(1958)によるとM=7.0, USCGSによるとMG=7.7と示されており,両者の決定値には著しい違いがある.一方,余震は札幌において多数観測され,P-S頻度分布は10 secから33 secの範囲にあつて,余震域の長さは約190kmと推定されている(宇津,1961)

著者

半田 駿

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.73, no.3/4, pp.345-359, 1999-03-29

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The MT survey was conducted to clarify the lower crustal resistivity structure beneath the volcanoes of Tsurumi- and Yufu-Dake in central Kyushu, SW Japan. The 2-D resistivity model obtained reveals that the highly resistive lower crust lies under highly conductive layers with a thickness of about 3 km at a shallow part of the crust. Since the resistive lower crust is also found in the Aso Volcano area, the present result implies that the lower crust is commonly resistive beneath volcanoes of the volcanic front in central Kyushu, while conductive layers are found at the middle and lower crust beneath the volcanic zone in many subduction zones, as seen in NE Japan.