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.46, no.1, pp.53-74, 1968-03

被引用文献数

2

---

Local migration of the seismic activity before and after the great Sanriku earthquake of March 3, 1933 in northern Japan is described. This remarkable migration pattern in the most active seismic zone in the world is compared with that of the Anatolia earthquakes accompanied by successive development of a great faulting system. The global migration of the epicentral regions of the greatest earthquakes during the last 30 years is summarized. The two northward migration branches in the western part of the circum-Pacific belt and in the Sumatra-Burma-Kansu-Baikal seismic zone and the one southward branch in the south-eastern part of the circum-Pacific belt, which are confirmed by certain evidence, suggest a clockwise rotational migration pattern in the circum-Pacific belt and the surrounding area or a worldwide migration pattern from the equatorial region to the pole regions. These migration patterns may provide an important suggestion on the mechaism of earthquake generation.|地震の震源域が時間と共に系統的に移動する場合があるかどうかという問題は,地震の発生を予測する問題にも関連して,古くから多くの人によって論じられてきた.余震域の拡大の様な,比較的短期間の局地的な移動については,2,3のかなり明瞭な移動の例が報告されているが,最も興味ある所の大きい地震の大規模な移動に関しては,これまでいくつかの報告例があるにも拘らず,その資料は,移動を結論するには不十分な場合が多く,移動が確実に結論され得る例は非常に少ない.従って,この問題については,確実に震源域の移動を結論出来る例を出来るだけ多く見出して,その移動特性を明らかにすることが重要である.本論文では,次に述べる,1933年3月3日の三陸沖大地震前後約6年間の移動及び過去30年間の巨大地震の震源域の世界的規模における移動について論ずる.

著者

Hamada Kazuo Hagiwara Takahiro

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.44, no.3, pp.1239-1268, 1967-01-30

---

The first high sensitivity tripatite observation was made at Hoshina, Nagano Prefecture in the period from October 31 to December 18, 1965 and the observational result has been reported as the first report. This paper is the report of the result of the second observation by the same method in the same region, observation starting again on February 20, 1966 after an interruption of sixty days and continuing through the end of June, 1966. This paper is confined to the result obtained in the period from February 20 to June 20, 1966. In the first observation, we have found that the locations of the seismic foci determined by our tripartite method were perceptibly accurate. Therefore, in the second observation, the sensitivity of the instruments was raised higher than the first observation and we registered a large number of ultra-micro earthquakes. The recorded earthquakes were analyzed and the locations of the seismic foci were determined immediately after the observation. Thus, the second observation by our tripartite method was used as a lookout in the area of Matsushiro Earthquakes. For that reason the work of analysis of the earthquakes including the calculation by an electronic computer was consolidated thus raising the efficiency of the work. As regards the methods of observation and determination of the seismic foci, we used the same methods as described in the first report, so we omit description of the methods in this paper reporting only the results of the observation.第1回の高感度3点方式による松代地震の観測は, 1965年10月31日から12月18日にかけて行われ,その結果を第1報として報告した.この報告は同じ地域で同じ方法による地震観測の第2報である.第2回の観測は第1回観測から60日の間を置いて1966年2月20日から再開され6月末現在なお継続中である.この報告は1966年2月20日から6月20日までの観測結果についてのものである.第1回観測結果から,われわれの3点方式によって定めた震源の位置が比較的良く定まっていることがわかった.そこで今回はもう少し感度を上げ,短時間に多くの極微小地震を観測し,直ちに解析を行ない,主に震源の位置を調べて松代地震地域における1つの監視として役立てることにした.そのために又電子計算機を中心とする解析作業を整備し,能率化して対処した.

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.56, no.4, pp.629-640, 1982-03-31

---

Two small tsunamis generated far off Iwate on Feb. 20,1979 and off Miyagi on Jan. 19, 1981 are investigated, by using the tide-gauge records. From the amplitude-distance diagram, the magnitude (Imamura-Iida scale: m) of the 1979 and 1981 tsunamis are determined to be m = -0.5 and 0, respectively. The source area of the 1979 Iwateoki tsunami was located near the Japan Trench and the length was 50 km. The source area of the 1981 tsunami lay on the east side of the 1978 Miyagi-oki tsunami (m=0.5) and the length was 60 km in an east-west direction. These source dimensions are nearly standard for earthquakes of magnitude (M 6.5-7.0). In the space distribution of tsunami sources during the past 85 years (1897-1981), a remarkable seismic gap can be seen in a segment of 150-200 km along the trench far off Miyagi. In the southern Sanriku region, no event has occurred for at least 85 years since the earthquake of Aug. 5,1897 (M=7.7). This 1897 tsunami (m=2) caused much damage to houses with waves 2-3 meters high. A segment of 200 km far off Miyagi should be considered as an area of relatively high tsunami risk.1978年宮城県沖地震後,この3年間に岩手と宮城県沖に2個の小津波が発生し,本所の江ノ島津波観測所をはじめ沿岸各地の検潮所で観測された.津波の概況は次の通りである.1)1979年2月20日の岩手沖津波岩手県はるか沖合の海溝付近の地震(M=6.5)に伴った津波である.岩手・宮城沿岸で全振幅10~20cm,周期5~8分の波が記録された.筆者の方法によれば,津波の規模(今村・飯田スケール,m)はm=-0.5と判定される.津波の逆伝播図から,推定波源域の長さは50km,面積1.6×103km2であった.2)1981年1月19日の宮城沖津波1978年宮城県沖地震より沖合におきた地震(M=7.0)によるもので,宮城・岩手沿岸で津波の全振幅20~30cm,周期は10分前後であった.津波の規模はm=Oと格付けされ,1978年津波(m=0.5)のエネルギーの約1/2である.推定波源域は東西方向に伸び,長さ60km,面積にして1.9×103km2である.両波源域ともほぼ余震域と合致しており,津波初動がいずれもみな押し波で記録され,その振幅の大きさから,波源域の海底が10数cm隆起したことを考えさせる.また,地震規模に比べ,1979年津波の規模はやや大きく,1981年津波は標準的であったといえる.これらの津波データを加え,最近85年間における三陸沖の波源域分布をみると,宮城県はるか沖合の海溝ぞい150kmの区間が地震の空白域として,目立ってきた.この海域は1897年8月に,中規模の津波(m=2)がおきたところである.この津波は,宮城県桃生・牡鹿郡の沿岸に2~3mの波高を記録し,200戸ほどに浸水被害を与えた.それからすでに85年が経過し,1897年津波の発生域が,その周辺の津波活動からみて,再発の可能性の高い海域と考えられる.

著者

阿部 勝征 高橋 正義

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.62, no.2, pp.p149-162, 1987-10

---

1986年11月21日に伊豆大島のカルデラ床で発生した割れ目噴火について,外輪山北東端と元町郊外で撮影したスチール・フィルムなどをもとに外形上の発達の推移を調べた.三原山の山頂火口から北へ約1km離れたカルデラ床でF1が16時15分に開口し,白煙に続いて灰色の噴煙と赤熱物が噴出した.追いかけるようにF1の南東側にF2が開口した.続いて,16時27分にF3がF2の南東側に,16時40分にF4がF3の南東側にそれぞれ開口した.全体としてみれば,噴火割れ目は北西から南東に,低地から高地に向けて次々に開口した.各割れ目は開口直後に約25m/minの速さで両方向にそれぞれ拡大した.噴火割れ目からの赤熱噴出物は火のカーテンの観を呈した.F1とF2は一列の噴火割れ目になり,それとF3はミ型に雁行した.噴火の勢いは16時50分頃から著しく増大した.火柱の高さはそれまで平均15m/minで増していたが,16時50分過ぎから100m/minの速さに変わった.火柱の高さは17時10分頃に最高の1.6kmに達し,その後しだいに低くなった.火口列の全長はちょうど1.0kmに達した.On the evening of November 21, 1986, new fissure eruptions occurred on the caldera floor of Izu-Oshima Volcano, Japan. The sequence of their formation is studied on the basis of time-printed photographs which were taken in succession by the authors at close range during the eruption. Shortly after 2 p.m., earthquakes began to increase in number. At 4 : 15 p. m. (7 : 15 a. m. in UT), the first eruption began with the opening of a small fissure from which gas started to rise into the air and then red-hot material spurted up. This outburst was about 1 km north of the summit pit of Mt. Miharayama. At about the same time the second outburst broke out 150 m to the southeast. At 4: 27 p.m., en echelon fissure started to open 110 m farther southeast. During the early stage of eruptions, individual fissures extended, with an average speed of 25 m/ min, both to the northwest and to the southeast across the caldera floor. Red-hot scorias with enormous clouds squirted from many points along fissures in the form of a nearly continuous line of eruptive fountains, producing a curtain of fire. The fountains gradually grew in height with an average speed of 15m/min. By 4: 40 p.m., the curtain of fire reached a height of 440 m and a length of 870 m. During the eruption, deep rumblings emanating from fountains were heard, and numerous earthquakes were felt. At 4: 40 p.m., a new eruption occurred 70 m farther southeast at the flank of Mt. Mihara-yama. On the assumption that the eruptive activity migrated to the southeast due to a rise of local dyke, an average rate of the rise is estimated to be about 3 m/ min. Shortly after 4: 50 p.m., the eruptive phase markedly increased in violence and changed form from fire fountains to some red-hot pillars. The pillars grew rapidly higher with an average velocity of 100 m/min. They reached maximum heights of 1.6 km at 5: 10 p.m. By that time, the fissure zone extended as much as 10 km long and consisted of four individual fissures 140-440 m in length. Lava from fissures spread out to form fan-shaped flows to the north-northwest and to the northeast of the caldera floor. The activity started to decline around 6 p.m. and ceased at about 11p.m., having lasted 7 hours. Although no lives were lost, a series of violent eruptions on November 21 forced all 10,000 islanders to evacuate Izu-Oshima island temporarily.

著者

松原 誠 小原 一成

出版者

東京大学地震研究所

雑誌

地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.84, no.4, pp.331-344, 2009

---

Many researchers have studied the three-dimensinal seismic velocity structure beneath the Kanto region, central Japan using seismic tomography, because the structure is very complicated due to subducting of the Pacific and the Philippine Sea plates beneath the Eurasian plate. The Tokyo metropolitan area is located in the Kanto region. Initially, the subducting Pacific and Philippine Sea plates are imaged with high-velocity zones. With many data, the oceanic crust at the uppermost part of the subducting Philippine Sea plate was imaged clearly. After construction of the NIED Hi-net, the oceanic ocrust of the Pacific plate subducting to depths over 100km was also imaged. A large low-velocity region at depths of 30-50km beneath the central Kanto region in the east-west direction was found by many researchers. The reason for the low-velocity is considered to be the existence of a serpentinied mantle wedge, curling Eurasian crust, and thick oceanic crust of the Philippine Sea plate. A low-velocity zone at depths of 40-70km beneath the eastern Kanto region with north-south direction was also found. The reason for this low-velocity is considered to be the existence of serpentinied mantle wedge and curling Philippine Sea plate. A high-density seismograph network, called MeSO-net, is under construction in this metropolitan region. The results with these data are expected to reveal a more detailed structure beneath the metropolitan area. We review former studies on the velocity structures beneath the Kanto region and note some characteristic structures beneath the Kanto region with results along arrays of MeSO-net.

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.60, no.3, pp.401-428, 1986-02-07

---

過去数10年にわたる大きい地震及び近年の徴小池震の線状配列から,男鹿半島と牡鹿半島を通って東北地方を横切る北西-南東の活構造線の存在が推定される.海底地形や地殻変動のデータもこの存在を示唆する.1983年の日本海中部地震は,この構造線が日本海東縁の構造境界に会合するという特異な場所で起ったもので,その余震の分布の特徴もこのことを示している.日本海溝,男鹿半島-牡鹿半島構造線,日本海東縁の構造境界及び北海道と本州の間の境界によって囲まれた地域が一つのブロックを形成し,これが東西圧縮応力場にある.日本海中部地震はこの東西圧縮応力が特に集中しやすい所に起った地震であり,ここでは日本海側としては例外的に大きい地震がくり返し起ってきた.1978年宮城県沖地震の震源域では大地震が頻繁に繰返し発生しているが,ここも男鹿半島-牡鹿半島構造線が日本海溝沿いのSubduction Zoneに達したという構造的に特異な所である.

著者

Horai Ki'iti

出版者

東京大学地震研究所

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.37, no.4, pp.571-592, 1960-01-30

---

From 68 measurements of rock temperature made at various points in drifts of Hitachi copper mine, geothermal gradients at these places were determined. The thermal gradient was found to be 0.94×1O-2℃/m and 1.21×10-2℃/m in the north and the south parts of the mine respectively. Thermal conductivity of 36 rock specimens collected from various parts of the mine was measured using the divided-bar method. Apparent thermal conductivities of the rocks at the two parts are 6.73~7.08×10-3 cal/cm sec℃ and 6.50~7.43×10-3 cal/cm sec℃. The terrestrial heat flow from the interior to the surface of the earth was computed to be 0.63~0.67×10-6 cal/cm2 sec for the north part and 0.78~0.90×10-6 cal/cm2 sec for the south part. These values are a little smaller than those already found in Japan.茨城県日立市日立鉱山に於ける地下温度勾配及び岩石熱伝導率測定の結果,鉱山の北部及び南部の二地域で温度勾配はそれそれ0.94℃/100m,1.21℃/100mであること及び等温面がほぼ地表面に平行すなわち熱流の方向がほぼ地表面に垂直であることを見出した.又岩石熱伝導率測定値にもとづいて北部及び南部二地域の見かけの熱伝導率は6.73~7.08×10-3cal/cm sec℃及び6.51~7.43×10-3cal/cm sec℃であると算定された.これによると,地殻内熱流量は北部に於て0.63~0.67×10-6cal/cm2 sec,南部に於て0.79~0.90×10-6cal/cm2 secとなるが,この値は第一報に報告された笹子トンネルに於ける結果2.06×10-6cal/cm2 secよりも低いのみならず世界の平均とされている1.20×10-6cal/cm2 secよりもなお低いようである.ここに求められた結果が,地殻内の局地的異常を表わすものか,或いは更に大規模な現象,中間層に於ける熱対流など,に関連あるものであるかどうかを追求するためには,更にこの程の研究の成果の集積をまたねばならない.

著者

Uyeda Seiya Horai Ki-iti

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.41, no.1, pp.83-107, 1963-06-30

---

Eight sets of new data on the terrestrial heat flow have been added to the existing five sets of data in Kanto and Chubu Districts, or the central part of Japan. Of the eight new localities, seven are in metal mines and one in a natural gas field. Expressing the geothermal gradient ΔT/ΔZ in ℃/100 m, and the heat flow in 10-6 cal/cm2 sec, the present data can be summarized as: Mobara: ΔT/ΔZ=1.85, Q=0.54 Ashio: ΔT/ΔZ=3.57, Q=2.23 Chichibu: ΔT/ΔZ=1.90, Q=1.34 Kamioka: ΔT/ΔZ=2.77, Q=1.80 Nakatatsu: ΔT/ΔZ=2.90, Q=1.95 Kune: ΔT/ΔZ=1.97, Q=1.60 (Honzan) ΔT/ΔZ=2.17, Q=1.44 (Nako) Minenosawa: ΔT/ΔZ=2.82, Q=1-79 Combined with previous data, the above figures indicate the following facts: a) Heat flow on the Pacific coast side of Kanto District is, without exception, small (Q<1.00); b) High heat flow region, known on the Japan Sea coast side of Tohoku District (Q>2.00) extends to the north-western part of Kanto District and possibly down to the Izu-Mariana Arc. This high heat flow region apparently coincides with that of Tertiary volcanism of Japan, c) Heat flow in Chubu District is higher than the world's average (Q = 1.2~1.4) but not very much. This high value may be accounted for by the relatively thick crust of the District.1.1957年以来,地震研究所においては,日本全土における地殼熱流量分布の決定が試みられてきた.1961年以降には,日本鉱業協会,日本石炭協会,天然ガス鉱業会,帝国石油株式分社,東京大学地質学教室の渡辺武男教授,久野久教授他の大きな御協力を得て,全国の鉱山,炭礦,油田,ガス田等においてやや組織的な地熱測量が行なわれた.地球熱学第8報乃至第12報は,その結果の報告である,この仕事では,樋口重雄氏,山川一郎氏(日本鉱業協会),佐久洋氏,佐野孝一氏(石炭協会),橋爪義雄氏(天然ガス鉱業会),柴宮博氏(帝国石油株式会社),他多くの方々,並びに,各現場での数多の方々の御指導,御援助を得た.記して深甚の謝意を表明する.岩石熱伝度測定のための試料研磨にっいては,地震研究所渡辺佐技官に多大のお世話になつた.なお,この研究は地震研究所力武常次教授の全面的御援助の下に終始したものである.従来,関東地方,中部地方には,信頼し得る地殼熱流量,Q,の測定は5個であつた.すなわち,Qを10-6cal/cm2 secで表して,日立(Q=0.94~1.21),鹿島(Q=0.76),勝田(Q=0.91),東京大学構内(Q=0.74),笹子トンネル(Q=2.06),である.今回は,新たに,8個の測定が加えられた,その結果概要は以下の通りである.千葉県茂原: Q=0.54栃木県足尾: Q=2.23埼玉県秩父: Q=1.34岐阜県神岡: Q=1.80福井県中竜: Q=1.95静岡県久根: Q=1.60,(久根坑)Q=1.44,(名合坑)静岡県峰之沢: Q=1.79本文,第1図を参照しつつ,上記結果を検討すると,以下のことが明らかである.a)関東地方太平洋側では,地殻熱流量は例外なく小さい(Q<1.0).b)従来察知されていた,東北地方日本海側の地殻熱流量の大きい地域(Q>2.0)の延長が,関東地方西北部にもみられ,所謂,第三紀火成活動帯と一致している.この地域は,更に南にのび,伊豆マリアナ弧につながる可能性がある.c)中部地方の大部分は,世界的平均熱流量(Q=1.2~1.4)よりは大きい値を示すが,Q=2.0には至らない程度である.なお,この地方では,既報,草津白根地熱地帯での結果のごとく,熱流量が局地的異常を示した例もあるが,伊豆大島火山,丹那盆地,清越鉱山等,おそらくは地下水の流動のために,信頼するに足る地温勾配の得られない場合もあつた.各測点での記録は以下のごとくである.

著者

Kato Aitaro Sakaguchi Arito Yoshida Shingo Mochizuki Hiromine Kaneda Yoshiyuki

出版者

東京大学地震研究所

雑誌

地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.78, no.1, pp.83-90, 2003

---

We conducted permeability measurements of basalt sampled from an exhumed ancient fault zone in the Cretaceous Shimanto accretionary complex in Japan, in order to investigate permeability structure and evolution following shear failure. Permeability showed a strong reduction with increase in the effective confining pressure and temperature. Rapid sealing at elevated temperatures was observed during hold experiments following shear failure. The results indicate that the permeability of a subduction megathrust fault would rapidly decrease due to the precipitation of clay-like minerals and other minerals, and indicates the potential for high fluid pressure in fault zones.

著者

爆破地震動研究グループ

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.32, no.1, pp.79-86, 1954-06

---

三回にわたる石淵での大爆破による地震動の観測が終了して間もなく,我々は1952年12月7日に,場所も同じ東北地方の,しかも石淵の場合の観測の東西側線上に丁度のる,釜石市から15km程西によつた釜石鉱山における約30トンの火薬による大爆破の地震動を観測する機会にめぐまれた.19の臨時観測点のすべてがきれいな記録をうることに成功したと云う訳でないので, 1,2その決諭を次回にゆづる点を残す結果となつたか,少くとも今度の観測で認められた注意すべき点は,1.石淵の場合に見出された第三層に相当すると思われる層の中のP波の速度が,観測誤差の範囲をかなり外れて大きく出たということ.2.今迄日本では見出されなかつた8km/sec程度のP波の速度をもつ層が,約30km位の深さで見出されたこと.3.東方測線による結果は,石淵の場合の東西測線からえられた結果とよく一致し,この辺の東西方向に関する地殼構造は,これでかなりの確実性をおびるに至つたことである.尚,今回の観測に当つて多大の便宜を与えられた日鉄鉱業釜石鉱山,建設省,国鉄盛岡管理局,NHK技術部,盛岡県庁,東北電力,その他各方面の関係者に対してはここに厚くお礼を申し上げたい.なお,本研究は,文部省科学研究費によつてなされたものであることを附記して謝意を表する.

著者

笹谷 努 Yoshii Toshikatsu Ikami Akira Tanada Toshikazu Nishiki Tsukasa Kato Susumu

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.1, pp.p33-48, 1990-06

被引用文献数

5

---

In October 1982, a seismic refraction experiment was conducted by the Research Group for Explosion Seismology in the Miyota-Shikishima Profile in Nagano and Yamanashi Prefectures, central Japan. Five shots were fired on the 60 km-long profile. The upper crustal structure derived from travel-time data is simple and has a high velocity gradient; 4.0km/s at the surface to 6.0km/s at about 2.5km depth. Based on the amplitude-distance pattern of the refraction phases, we confirmed the existence of the velocity gradient. A few explosive sources generated clear S waves with amplitudes large enough to be read. We obtained an average POISSON'S ratio of around 0.246 in the uppermost crust from S to P travel time ratios. The other later arrivals were interpreted as reflected phases from a deep interface, the Conrad discontinuity. We modeled the interface shape by the ray-tracing technique. The interface inclines teward the north by about 20°.地震予知計画による4度目の爆破地震の実験が, 1982年10月,日本中部の長野県から山梨県にかけての御代田-敷島測線上で行われた. 60kmの測線上の5個所で爆破が行われ,約60点の臨時観測点で観測された.この実験の概要と,得られた記録や走時データなどの基礎的な資料については,すでに報告されている(爆破地震動研究グループ, 1986).ここでは,これらのデータの解析結果について報告する.

著者

Mogi Kiyoo

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.46, no.1, pp.53-74, 1968-03-19

---

Local migration of the seismic activity before and after the great Sanriku earthquake of March 3, 1933 in northern Japan is described. This remarkable migration pattern in the most active seismic zone in the world is compared with that of the Anatolia earthquakes accompanied by successive development of a great faulting system. The global migration of the epicentral regions of the greatest earthquakes during the last 30 years is summarized. The two northward migration branches in the western part of the circum-Pacific belt and in the Sumatra-Burma-Kansu-Baikal seismic zone and the one southward branch in the south-eastern part of the circum-Pacific belt, which are confirmed by certain evidence, suggest a clockwise rotational migration pattern in the circum-Pacific belt and the surrounding area or a worldwide migration pattern from the equatorial region to the pole regions. These migration patterns may provide an important suggestion on the mechaism of earthquake generation.|地震の震源域が時間と共に系統的に移動する場合があるかどうかという問題は,地震の発生を予測する問題にも関連して,古くから多くの人によって論じられてきた.余震域の拡大の様な,比較的短期間の局地的な移動については,2,3のかなり明瞭な移動の例が報告されているが,最も興味ある所の大きい地震の大規模な移動に関しては,これまでいくつかの報告例があるにも拘らず,その資料は,移動を結論するには不十分な場合が多く,移動が確実に結論され得る例は非常に少ない.従って,この問題については,確実に震源域の移動を結論出来る例を出来るだけ多く見出して,その移動特性を明らかにすることが重要である.本論文では,次に述べる,1933年3月3日の三陸沖大地震前後約6年間の移動及び過去30年間の巨大地震の震源域の世界的規模における移動について論ずる.

著者

Mogi Kiyoo

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.46, no.6, pp.1225-1236, 1969-03-17

---

To study the process of occurrence of shallow earthquakes in and near Japan, the space and the time distributions of focal regions of large earthquakes and the earthquake energy density during the period (1885-1968, May) have been investigated. The results are summarized as follows: (1) During the last eighty years, earthquakes occurred with the space distribution showing a close relation to tectonic structures of this region. (2) Great earthquakes in this region occurred to fill gaps of seismic activity of thirty years and over, as pointed out in other circum-Pacific regions. It is particularly remarked that any large earthquakes of magnitude 7 and over did not occur in the focal regions of great earthquakes during the preceding period. (3) The seismic activity in the Kwanto and the southern Tohoku districts, including the part of the outer seismic zone, is abnormally low in the last thirty years. If the high activity in the preceding fifty years in this region is considered, this result suggests a possibility that great events may occur in the region in the near future.|日本及びその周辺の地震活動の空間的分布並びにその時間的変化を,マグニチュード7以上の大きい地震の震源域の分布及び小さい地震を含めた地震エネルギー密度の分布から論じた.できるだけ長期間についてしらべることがのぞましいが,この目的のための地震資料は,1885年以降に限られる.この最近約80年間についての調査の結果を次に要約する

著者

齊田 時太郎

出版者

東京帝国大学地震研究所

雑誌

東京帝国大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.18, no.4, pp.692-697, 1940-12-30

---

It is reported that there were earthquake-proof buildings called "Disin no Ma" in the mansions of some of the feudal lords of ancient Japan. Recently the author investigated a "Disin no Ma" that was in a good state of preservation in the site of tha Hikone castle. This building was constructed two hundreds and sixty four years ago. The design of this structure is very striking and worthy of note from the standpoint of present structural engineering. The author points out the gret value of the structure in studying the historical development of earthquake-proof construction in Japan.

著者

萩原 尊禮

出版者

東京帝国大学地震研究所

雑誌

東京帝国大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.17, no.3, pp.627-637, 1939-09-20

---

A strong earthquake occurred in the neighbourhood of Ogasima, a small peninsula in Akita Prefecture, at 14 h 58m, May 1st, 1939. Shocks of the same magnitude occurred twice with an interval of 2 minutes. Several hundreds of dwelling houses in the peninsula were demolished and 29 persons killed. The damage was increased by the landslip caused by the earthquake. The number of houses demolished as the direct result of the earthquake shock are shown in Fig. 2.

著者

地震研究所地震観測班地震計測部 the Seismometrical Section

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.45, no.3, pp.887-917, 1967-11

---

The Matsushiro earthquake swarm commenced in August 1965 and continues even at present when more than a year and a half has passed since the outbreak. For the sake of convenience, we divided the activity of this earthquake swarm into four stages. The first stage of activity: This was the period from the outbreak of the earthquake swarm to February 1966, the highest peak of the activity occcurring in November 1965. The main shocks took place around Mt. Minakami, especially on its southwestern side, during this period. Shocks were not felt so frequently as later at Hoshina at that time. The second stage of activity: This began in March 1966 and continued to the beginning of June 1966. The activity at this time was most violent throughout the whole period, the area of seismic activity extending to a broader area of Matsushiro and Wakaho. In April 1966, the frequency of earthquakes reached the maximum throughout the whole period and large shocks with intensity of IV or V on the JMA scale took place frequently, inflicting some damage on dwelling houses and other constructions in this area. The third period of activity: This continued from August to October 1966. The seismic active area in this period was mainly at Matsushiro and Wakaho as was in the second period but it extended gradually to the eastern part of Koshoku and to the northern part of Sanada. Large shocks with intensity of IV or V on the JMA scale also occurred during this period. In November 1966, the frequency of earthqakes decreased greatly compared with the previous month and large shocks also did not take place. The fourth stage of activity: We call the period from January to the present the fourth stage of activity. The special feature of this stage was that the earthquakes that had clustered in the area of Matsushiro in the earlier stages of activity decreased in number remarkably, while the seismic area extended widely northeastward and southwestward, many shocks taking place in a part of Wakaho and in the southern part of Mt. Kamuriki. This paper will compile the result of our seismographic observation carried out during the period from December 1966 to February 1967 as the fourth report continuing from our previous ones. The seismographs used at each station were the HES 1-0.2 electromagnetic seismograph and the Ishimoto acceleration seismograph, of which the constants were indicated in Table 1 in our second report. The members of the Institute who participated in the field observation were: T. Hagiwara S. Saito, I. Karakama, M. Watanabe, T. Takahashi and Y. Ishikawa and the members of the Institute engaged in interpretation and analysis of seismograms being: T. Hagiwara, T. Iwata, K. Makino, N. Kamata, M. Kino, Y. Miura and R. Kawashima.1965年8月3日に始まる長野県松代町地域の群発地震は, 1967年2月28日に至る19カ月を,4つの地震活動期に分けて考えることができよう.第1期の地震活動 発生より1965年11月に至る期間で,このときの主な有感地震の発生地域は皆神山の周辺,特にその南西部で,大きな地震はすべてこの地域に発生した.なお,第1期では若穂町保科週辺に極めて少数の有感地震が認められている.

著者

萩原 尊禮

出版者

東京帝国大学地震研究所

雑誌

東京帝国大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.16, no.4, pp.779-783, 1938-11-20

---

A mud avalanche occurred at Mt. Tukuba, Ibaraki prefecture, on July 3, 1938. In flowing down the valley it swept away two wooden buildings and killed three men. The avalanche was caused by collapse of soil in the upper waters of the valley as the result of heavy rains. The velocity of the flow was estimated to be less than 10 meters per second.

著者

Fukao Yoshio Abe Katsuyuki

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.1-12, 1971-09-30

---

By a concept of normal mode theory, the realistic seismograms of Love waves are synthesized for the CIT11A spherical earth model. The synthetic seismograms, which include the effects of instrumental response and attenuation, are computed for fundamental and higher modes up to the third order. The source is assumed to be a double couple of body forces varying stepwise in time applied to a point. Calculations are made for various focal depths ranging from 30 to 530km. It is demonstrated that a strike-slip source excites Love waves by an order of magnitude larger in amplitude than a dip-slip source, and that the higher mode contribution relative to that of the fundamental mode is significantly large for a dip-slip source at any depth. The synthesized seismograms thus obtained facilitate the determination of various source parameters. The results are applied to an intermediate-depth earthquake in Eastern New Guinea on February 26, 1963 (d=182km). The seismic moment is estimated as 2.5×1027 dyne・cm.|現実的な地球モデルと震源モデルをもちいてラブ波の合成地震記象を作り,excitationに関する基本的な性質を調べ,実際の地震に応用してその有用性を確かめた.球状地球モデルとしては,CIT11Aを採用した.断層モデルと等価な震源モデルとして,点震源に時間関数がステップ状に変化する力より構成される復双力源を考えた.合成地震記象は基本および1次から3次までの高次の基準振動のモード解を周期約7秒から600秒の範囲で加えあわせることにより作られた.伝播媒質の減衰および地震計の特性を考慮することにより記象を現実的なものとした.震源の深さとしては30kmより530kmまでの範囲にわたつて選んだ.

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.59, no.1, pp.p115-125, 1984

被引用文献数

3

---

新史料を加え,1741年渡島沖津波の波高を再検討した.また,北海道渡島沿岸を現地調査し,熊石にある津波地蔵・過去帳を紹介した.津波の高さは渡島沿岸で10m,局地的には15mに達し,津軽で5~6m,佐渡では4~5mと推定される.津波マグニチュードは,Δ-Hグラフからm=3.5と見積もれる.波高分布のピークは1983年日本海中部津波のものより北側に片寄り,波源域は渡島半島沖の水深3,000mの海域を中心に,長さ150kmの範囲にあったと考える.Adding new data on the Oshima tsunami of Aug. 29, 1741, the inundation heights along the coast of the Japan Sea are reexamined. About 2,000 persons drowned at 22 villages within the 90 km stretch (Matsumae to Kumaishi) along the west coast of Oshima Peninsula, West Hokkaido. A religious monument and an old document were newly found at a temple in Kumaishi. Considering ground level, inundation heights (above sea level) of the tsunami along the Oshima coast were estimated to be 10m with local run-ups as much as 15m. The estimated inundation heights are 5-6m at Tsugaru (Aomori Pre.), 3-4m at Noto-Shitsura (Ishikawa Pre.), 1m at Obama (Fukui Pre.) and 1-2m at Gotsu (Shimane Pre.). The distribution pattern of the heights on Sado Island is highly similar to that of the 1983 NihonkaiChubu tsunami. However, the wave-period of the 1741 Oshima tsunami is longer than that of the 1983 tsunami, because the wave-heights are large in the big bays at Aburakawa and Ryotsu. Judging from the attenuation of tsunami height (semi-amplitude) with distance, the tsunami magnitude (Imamura-Iida scale) is m=3.5. The tsunami energy is five time larger than that of the 1983 tsunami (m=2.5). Compared to the magnitude and the distribution pattern of heights for the 1983 tsunami, this suggests that the source area of the 1741 tsunami extends about 150km along the bathymetric line 3,000m off the Oshima Peninsula.

著者

工藤 一嘉 坂上 実

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.59, no.2, pp.361-382, 1984-10-20

---

1983年日本海中部地震の発生に伴ない,震央から270kmも離れた新潟県下の大型石油タンクから石油が溢流した.地震により石油が溢流することは,石油コンビナートの耐震安全性を考える上で極めて重要な問題であり,盗流の原因となったスロッシングの発生状況,地震動の特徴について検討した.新潟における本震の地震観測記録類には,それぞれ欠陥があり,正確な地震動を把握できなかったが,以下のような特徴が見い出された.1.溢流の生じたタンクのスロッシング周期,8~11秒における速度応答は少なくとも100cm/sec以上で200cm/secは超えない.2.最大地動変位は10cmから20cmの間である.3.長周期で大振幅の地動変位は,表面波としての特徴を有し,新潟における厚い堆積層による増幅を受けた結果である.スロッシングに対する基本的理解は,新潟のデータを大勢としては説明するが,スロッシングが異常に大きい例もあり,基木的理解に検討を加える余地が残されている.溢流を発生させないために設定されている入力地震動レベル(速度応答=100cm/sec)は,全国平均で見れば相当安全側に考慮されていると言える.しかし新潟の事例から,地域性を含めたより詳細な規準値の設定が要請される.Oil sloshed from the huge oil tanks at Niigata due to the Nihonkai-Chubu earthquake of 1983, eventhough the epicenter was as far as 270km away. The oil sloshed out generally for periods of 8 to 11 seconds. The earthquake motions at Niigata were estimated by analyzing the displacement records and the accelerogram (SMAC) from the mainshock (M=7.7) and the accelerogram (digital recordings) from the June 21 aftershock (M=7.1). Because the horizontal components of displacement-meter were overloaded and the recorded amplitudes by the SMACB type accelerograph were too small to be analyzed exactly, the results obtained should have errors somewhat greater than we expected. However, it can be said with a certain degree of reliabilty that; 1) velocity responses of one mass system caused by the mainshock at Niigata in the periods from 8 to 11 sec. were over 100cm/sec but less than 200cm/sec, 2) the maximum ground displacement at Niigata was between 10cm and 20cm, 3) the long-period and large ground-displacements at Niigata were mostly composed of surface waves excited by the thick sedimentary layers at the site. The limit value prescribed by the regulation for the safety of oil sloshing from the tanks is defined as a velocity response of 100cm/sec. It can be said that the limit value of 100cm/sec is reasonable as an average in Japan, but it should be increased for some sites due to local seismic-wave amplifications. The data on sloshing obtained at Niigata roughly match the model for the sloshing of liquid in the cylndrical shell as it is generally understood, but the data that do not confirm to the model are included. So, clarification is needed on the scattering of the maximum sloshing wave heights as revealed in the data at Niigata.