著者

武村 雅之 浜田 信生

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.49, no.2, pp.141-168, 1996-08-23 (Released:2010-03-11)

参考文献数

35

被引用文献数

1

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96 photographs of seismograms from the 1923 Kanto earthquake (M=7.9) have been preserved at JMA (the Japan Meteorological Agency). These seismograms were obtained at meteorological observatories in and around Japan and Tohoku Imperial University in Sendai, whose epicentral distances are within about 2000km. P-wave forms of the main shock are recorded at 37 observation stations, though larger shaking parts of the ground motions are saturated on the records at almost all the stations. First, a type of seismograph and its instrumental characteristics are examined for each record from old materials and old records preserved at JMA. It is found that the seismograms at 29 stations were recorded by Portable Seismographs with natural period T of about 5sec and magnification V of 10 to 100, and most of the others by Omori's Seismographs with T of 10 to 30sec and V of 10 to 20 and by Wiechert Seismographs with T of about 5sec and V of about 100. Secondly, P-wave characteristics of each record are examined. We reexamined polarities of initial P-wave motions and reviewed focal mechanisms obtained for the Kanto earthquake. We also found that P-wave forms at many stations have some characteristics in common. The P-waves begin with small amplitude and the first remarkable phase with a large amplitude appears after the duration of the initial small phases. The second remarkable phase is also identified several seconds after the first remarkable phase, irrespective of the epicentral distances of the stations. The duration time τ01 of the initial small amplitudes correlates with the epicentral distance at each station. It can be explained by the difference of calculated arrival times between Pn and Pg phases or between Pn and P* phases in addition to a duration of the initial small rupture near the hypocenter. The duration of the initial small rupture is evaluated about 4.5sec from τ01's at observation stations within the epicentral distance of 170km. In the meantime, the difference τ12 of arrival times between the first and the second remarkable phases correlates with the azimuth angle of each station from the epicenter. Geometry and difference of occurrence times of big subevents are evaluated on the fault plane of the main shock from the data of τ12's, if we assume the two remarkable phases are due to two big subevents, respectively. The second subevent is located about 40km distant from the first subevent in the direction of about N 100°E, and the time interval of the occurrences of the two subevents is about 14sec.

著者

草野 富二雄 浜田 信生

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.44, no.4, pp.305-313, 1991-12-24 (Released:2010-03-11)

参考文献数

34

被引用文献数

2

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The focal process of the 1964 Niigata Earthquake was reinvestigated on the basis of hypocentral distribution of its aftershocks. This study indicates that the aftershocks are distributed on a fault plane dipping westward.Although it has been clear that the fault strike of the mainshock was in N20°E direction, the dip of the fault was not still clear due to a poor resolution of hypocenter of aftershocks. To resolve the difficulty, we reexamined seismological data obtained by the Japan Meteorological Agency (JMA).Reexamination of seismograms of nearby stations enabled us to supplement more than 1200 new P and S arrivals of aftershocks. We also dentified a number of P and S arrivals from the data which were previously reported as unidentified phases. The Joint Hypocenter Determination method was used to get a more reliable aftershocks distribution. The number of located aftershocks much increased, as about 380 aftershocks are well located by this study.Aftershocks on the vertical cross section which is normal to the fault strike shows that aftershocks are on a westward dipping plane. The dip of the plane is estimated as 50 degrees which is consistent with the focal mechanisms reported by several studies. Although the dip angle depends on the velocity model used in hypocenter location, westward dipping of aftershocks is valid, independent of several different velocity models. Therefore we estimate that the subduction of the Japan Sea under the north-east Honshu does not occur in the southern part of the eastern margin of the Japan Sea.The aftershock activity is found to be low around the hypocenter of mainshock which is located near the bottom of aftershock region, suggesting a large strain release around the nucleation point of mainshock. Relative position of forerunning seismic activity which preceded the mainshock by two years seems to be within the shallow part of the aftershock region east of Awashima-island which is located in the western middle of the focal region. The epicentral distribution of aftershocks indicates that aftershock occurrence is scarce around Awashima-island. A similar relation was reported in the case of the 1983 Nihonkai-chubu earthquake between its aftershocks and Kyurokujima-island, which is situated east of the middle of the aftershock region. Few aftershocks occurred in the area around Kyurokujima-island. In spite of the difference in relative location, that is, Awashima is situated west of the aftershock region while Kyurokujima is in the east, this suggests possibilities that crust around the islands cannot sustain enough strain to generate aftershocks or it behave as an earthquake barrier.

著者

上野 寛 森 博一 碓井 勇二 宮村 淳一 吉川 一光 浜田 信生

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.47, no.5, pp.689-694, 2002-11-29 (Released:2017-03-20)

参考文献数

14

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We studied high-frequency earthquake swarm associated with the eruption of the Usu volcano in 2000 using the data observed by a national seismic network in southern Hokkaido. To get a precise hypocenter location, we applied the double-difference method and station correction to hypocenter determination. Systematic shift of epicenters possibly caused by heterogeneous velocity structure of the upper crust is needed to be consistent with the initial motions of the seismograms at the nearest station. Concentration of hypocenters under the northern flank of the volcano in the initial stage suggests that the magma started its activity at about 5 km in depth at the region. Concentric expansion of swarm area occurred before the eruption and formed doughnut pattern of which center is located near the summit of the volcano. Doughnut pattern may represent relaxation of stress under the volcano which is caused by magma movement and pore pressure change under the volcano.

著者

浜田 信生

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.2, pp.132-144, 2001-04-25 (Released:2009-11-12)

参考文献数

20

被引用文献数

5 4

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Based on macro seismic and instrumental observation data covering a period of over hundred years, the characteristics of seismic activity around Miyakejima, Kozushima, and Niijima, the northern Izu islands, were investigated. Seismic activity is distributed along the Zenisu ridge and the Nishi-Shitito ridge to the west and along Niijima, Miyakejima, Mikurajima and Hachijojima islands to the east. Most of the seismic activity in the region is of the swarm type and is often induced by a large earthquake or magmatic activity at Miyakejima and other volcanoes. Comparison of macro-seismic data of large earthquakes in the late 1800s and the early 1900s with a seismic intensity map of recent earthquakes suggested that the maximum size of an earthquake in the region is around a magnitude of 6.5 on the JMA magnitude scale. Linear arrangements of seismicity in the NE-SW direction, which is parallel with the Zenisu ridge, and in the NW-SE direction, which is almost normal to the former and parallel to the direction of the plate motion of the Philippine Sea plate, are often recognized. While the strike slip-type earthquake with a NE-SW tension axis is predominant in the region along Niijima, Miyakejima, Mikurajima, and Hachijojima islands, a strike slip with E-W tension axis is predominant in the region along the Zenisu ridge and the Nishi-Shitito ridge. A complex tectonic setting of the region, back arc spreading, collision of the Philippine Sea plate to the Eurasian plate around the Izu peninsula, deformation of the plate due to the subduction of slab from the Suruga and the Sagami trough, must shape the characteristics of seismic activity in the region such as the upper limit of earthquake scale, swarm-type activity, close relation with volcanic activity, and regional stress pattern.

著者

浜田 信生

出版者

気象庁気象研究所

雑誌

Papers in Meteorology and Geophysics (ISSN:0031126X)

巻号頁・発行日

vol.38, no.2, pp.77-156, 1987 (Released:2007-03-09)

参考文献数

224

被引用文献数

12 8

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長い時間スケールを持つ地震活動に対し、古い地震資料の精度の再評価による解明を試みた。まず過去60年間の地震観測の歴史を概観し、観測体制、運用状況を考察することにより、観測の精度、地震検知能力がどのように変化したかを把握した。次に観測の時間精度と震源決定精度の関係を、各時代につき実際例から調べ、古い観測資料の精度が今までの研究では、過小評価されてきたことを明らかにした。二重深発地震面、大地震の余震域の形状と本震の震源過程などについて行われている最近の解析方法が、古い地震活動についても適用可能となったばかりでなく、新たにサイスミシティの経年変化などを追跡する道が開けた。以上の結果を踏まえて、1940年代から1960年代にかけて日本列島の内陸部で発生した、主な被害地震の本震余震分布の再調査を進めた。再調査の結果から、いわゆる直下型地震の震源過程、先行地震活動や前震活動、余震活動の減衰の仕方など、今日の地震学の一般的な問題について考察を加え、幾つかの結論を導いた。

著者

岩田 孝仁 浜田 信生

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.39, no.4, pp.621-634, 1986-12-25 (Released:2010-03-11)

参考文献数

18

被引用文献数

1 1

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In the present study, we have accumulated most complete seismological data and reinvestigated the seismicity associated with the 1944 Tonankai earthquake. Because of poor observation and social difficulty during the World War II, incompleteness and insufficiency in observational data resulted in rather obscure view about the actual process and mechanism of the earthquake. Number of aftershocks and their location accuracy reported by existing studies seem to be dissatisfactory for detailed discussion.We found some observational data that are still available but have not been used yet, then, we applied a modern hypocenter location method to the newly compiled data and succeeded in increasing the number of accurately located aftershocks more than twice. The followings are important findings of the study.The mainshock initiated from the bottom of the fault plane, in the south-west corner of the focal region. This feature is in accordance with the results of some previous studies. Most of aftershocks concentrated in the vicinity of the Shima spur, which extends south-east from the Shima peninsula to the Nankai trough. Temporal broadening of the aftershock region toward south-east along the spur is recognized and this trend seems to continue over 40 years until now. Distribution of aftershocks around Shionomisaki, the southern top of the Kii peninsula, may suggest some overlapping of the focal regions of the Tonankai and the 1946 Nankaido earthquake. Aftershock activity or induced seismicity is also recognized in the middle part of Shizuoka prefecture where some seismologists assume the focal region of a future interplate earthquake, so called Tokai earthquake. Seismicity around the southern Izu peninsula may represent an induced activity along one of the active faults which strikes southeast from the peninsula. Other induced seismic activity in inland area of central Honshu indicates a large extent of the effect of the interplate earthquake on the tectonic environment of the mentioned area. This study will contribute to gain better understanding of the process and mechanism of the Tonankai earthquake.

著者

田中 実 浜田 信生

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 1991.2 (ISSN:24335320)

巻号頁・発行日

pp.159, 1991-10-14 (Released:2017-02-10)

著者

浜田 信生

出版者

気象庁気象研究所

雑誌

気象研究所研究報告 (ISSN:0031126X)

巻号頁・発行日

vol.38, no.2, pp.77-156, 1987

被引用文献数

8

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長い時間スケールを持つ地震活動に対し、古い地震資料の精度の再評価による解明を試みた。まず過去60年間の地震観測の歴史を概観し、観測体制、運用状況を考察することにより、観測の精度、地震検知能力がどのように変化したかを把握した。次に観測の時間精度と震源決定精度の関係を、各時代につき実際例から調べ、古い観測資料の精度が今までの研究では、過小評価されてきたことを明らかにした。二重深発地震面、大地震の余震域の形状と本震の震源過程などについて行われている最近の解析方法が、古い地震活動についても適用可能となったばかりでなく、新たにサイスミシティの経年変化などを追跡する道が開けた。以上の結果を踏まえて、1940年代から1960年代にかけて日本列島の内陸部で発生した、主な被害地震の本震余震分布の再調査を進めた。再調査の結果から、いわゆる直下型地震の震源過程、先行地震活動や前震活動、余震活動の減衰の仕方など、今日の地震学の一般的な問題について考察を加え、幾つかの結論を導いた。

著者

浜田 信生 野坂 大輔 小林 正志 吉川 一光 石垣 祐三 田利 信二朗

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.64, no.4, pp.197-209, 2012-06-25 (Released:2012-08-08)

参考文献数

28

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Matsushiro earthquake swarm is a most well known and well studied earthquake swarm in the history of seismology. From viewpoints of geophysics, geology and geochemistry, various observations, field surveys and analyses had been made to reveal characteristics of the swarm. On the basis of these studies, several models had been proposed to explain why and how the swarm originated and developed. However, majority of studies had focused on the activity around the climatic stage of the swarm in 1966 and so far, studies on the initial stage of the swarm in mid 1965 had remained few due to lack of sufficient observation data. The exact area where the swarm was born had not been known and the swarm was vaguely believed to originate from the area around Mt. Minakami in former Matsushiro town (now belongs to Nagano city). Considering that the manner of initial development of swarm activity represents an important characteristic of the swarm earthquake, we tried to get more clear view about initial stage of the swarm activity in this study. We re-investigated seismograms obtained by routine observation and studied seismograms of temporal stations for the first time which had not been processed yet. By scanning analogue seismograms, we made a complete data set of S-P times with high precision for each station. Although the data set of S-P times from two stations are not sufficient for conventional hypocenter location, we were able to narrow down a possible source area of the swarm activity under the reasonable assumptions. By considering direction of initial motion of P waves and assuming local velocity model of the upper crust in the region and plausible focal depth of 4.5km of the swarm earthquake, we found that the area of swarm in the very beginning in August, 1965 is located about 4km north-east of the Matsushiro earthquake fault (MEF) in former Wakaho town near its border with former Matsushiro town. Size of the initial swarm area was 3-4km in diameter. While swarm activity in the initial region was gradually decaying in September new swarm activity appeared separately from the initial swarm area around southern and south-west part of the MEF. Activity in the new swarm area had been increasing and it was developed to more intense swarm after October, 1965 when establishment of temporal seismic station network of the Earthquake Research Institute, University of Tokyo enabled detailed hypocenter location. The new swarm area coincides with the area where large amount of ground water moved upward and was released on the ground surface in the climatic stage of the swarm. It was well known that source area of the swarm was split and expanded toward north-east and south-west after March, 1967 in its climatic stage. Present study on the initial development of swarm area suggested that characteristics of the Matsushiro earthquake swarm such as splitting and expansion of its source area toward northeast and southwest were inherent in their early stage of the activity in August and September, 1965.

著者

山田 功夫 深尾 良夫 深尾 良夫 浜田 信生 鷹野 澄 笠原 順三 須田 直樹 WALKER D.A. 浜田 信夫 山田 功夫

出版者

名古屋大学

雑誌

国際学術研究

巻号頁・発行日

1992

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我々はPATS(ポンペイ農業商業学校)や現地邦人の方々の協力を得て,平成5年3月ミクロネシア連邦ポンペイに地震観測点を開設することができた.平成4年9月の現地調査以後,手紙とファクスのみでのやりとりのため,現地での準備の進行に不安があったが,現地邦人の方々のご協力もあって,我々は計画を予定どうり進めることができた.その後,地震観測の開設は順調に進んだが,我々の最初の計画とは異なり,電話が使えない(最初の現地調査の際,電話の会社を訪ね相談したとき,「現在ポンペイ全体の電話線の敷設計画が進んでおり,間もなくPATSにもとどく.平成5年3月であれば間違いなくPATSで電話を使うことができる」とのことであったが,工事が伸びた).このため最初に予定した,電話回線を使った,観測システムの管理やデータ収集はできなくなった.近い内に電話回線を利用することもできるようになるであろうことから,観測システムの予定した機能はそのままにし,現地集録の機能をつけ加えた.そして,システム管理については,我々が予定より回数を多く現地を訪問することでカバーすることにして観測はスターとした.実際に観測初期には色々な問題が生じることは予想されるので,その方が効率的でもあった.現地での記録は130MバイトのMOディスクに集録することにした.MOディスクの交換は非常に簡単なので,2週間に1度交換し,郵送してもらうことにした.この記録の交換はPATSの先生にお願いすることができた.実際に電話回線がこの学校まで伸び,利用できるようになったのは平成6年1月のことであった.よって,これ以後は最初の予定通り,国際電話を使った地震観測システムが稼働した.観測を進める中で,いくつかの問題が生じた.(1)この国ではまだ停電が多いので無停電装置(通電時にバッテリ-に充電しておき,短い時間であればこれでバックアップする)を準備したが,バックアップ時ははもちろん,充電時にもノイズが出ているようで,我々のシステムを設置した付近のラジオにノイズが入るので止めざるを得なかった.(2)地震観測では精度の良い時刻を必要とする.我々はOMEGA航法システムの電波を使った時計を用意したが,観測システム内のコンピューター等のノイズで受信状態が悪く,時々十分な精度を保つことができなかった.結局,GPS衛星航法システムを使った時計を開発し,これを使った.このような改良を加えることによって,PATSでは良好な観測ができるようになった.この観測点は大変興味深い場所にある.北側のマリアナ諸島に起こる地震は,地球上で最古のプレート(太平洋プレートの西の端で1億6千万年前)だけを伝播してきて観測される.一方,ソロモン諸島など南から来る地震波はオントンジャワ海台と言われる,海底の溶岩台地からなる厚い地殻地帯を通ってくる.両方とも地震波はほとんどその地域だけを通ってくるので,地殻構造を求めるにも,複雑な手続きはいらない.これまでにも,これらの地域での地殻構造に関する研究は断片的にはあるが,上部マントルに至るまでの総合的な研究はまだ無い.マリアナ地域で起こった地震で,PATSで観測された地震の長周期表面波(レーリー波)の群速度を求めると,非常に速く,Michell and Yu(1980)が求めた1億年以上のプレートでの表面波の速度よりさらに速い.このレーリー波の群速度の分散曲線から地下構造を求めてみると,ここには100kmを越える厚さのプレートが存在することが分かった.一方,オントンジャワ海台を通るレーリー波の群速度は,異常に遅く,特に短周期側で顕著である.この分散曲線から地下構造を求めると,海洋にも関わらず30kmもの厚い地殻が存在することになる.これは,前に述べたように,広大な海底の溶岩台地の広がりを示唆する.同様のことは地震のP波初動の到着時間の標準走時からの差にも現れている.すなわち,マリアナ海盆を伝播したP波初動は標準走時より3〜4秒速く,オントンジャワ海台をとおる波は2〜3秒遅い.この観測では沢山の地震が記録されており,解析はまだ十分に進んでいない.ここに示した結果は,ごく一部の解析結果であり,さらに詳しい解析を進める予定である.

著者

浜田 信生

出版者

一般社団法人電子情報通信学会

雑誌

電子情報通信学会ソサイエティ大会講演論文集

巻号頁・発行日

vol.2005, no.1, pp."SS-10"-"SS-11", 2005-09-07