著者

村井 勇 角田 信子 辻村 芳子

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.53, no.3, pp.1025-1068, 1978-12-25

著者

羽鳥 徳太郎

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.53, no.3, pp.855-861, 1978-12-25

著者

Takeo Minoru Mikami Naoya

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

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

---

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

森本 良平 松田 時彦

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.39, no.4, pp.935-942, 1962-03-15

---

The area around Mt. Gankyoji-yama, 45 km east of Fukui City and 70 km north of Gifu Gity, was attacked by a severe earthquake at 14 h 33 m on August 19, 1961 (The earthquake was later named as Kita Mino Earthquake). In this area, in addition to the damage done to houses and stone walls, fissures were opened on narrow ridges. Many rock fall and earth fall took places on the steep cliffs.

著者

宮村 攝三 堀 実 安芸 敬一 松本 英照 安藤 誠一

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.39, no.4, pp.895-908, 1962-03-15

---

1961年8月19日岐阜,福井,石川3県境界付近に発生した北美浜地震にともなう余震群を,本震震央南南西30kmの岐阜県郡上郡八幡町において8月27日より約1ケ月間磁気テープ記録による多成分観測装置によつて観測した.辺長1kmにちかい3点観測によつて初詣の到来方向,みかけの速度をもとめ余震群の分布を現地でただちに推定することができたが,それによると余震域は本震震央の西方にひろがるごくせまい面積をしめ,深度はO~25kmの地殼内にかぎられることがわかつた.余震域の面積A(km2)は本震の規模(M=7.2)から宇津・関の公式logA=M-4で推定されるものにくらべいちぢるしくせまい.なお余震群以外の局地的小地震が観測されたことも注目にあたいする結果である.|After the Kita Mino (North Mino) Earthquake of August 19th, 1961, we hurried to Hachiman, Gujo County, Gifu Prefecture, Central Japan, about 30 kms south-east of the epicenter to observe its aftershock activity for several weeks. Tripartite stations were occupied, as shown in the map of Fig. 1, near the temporary observation room at Gujo High School and from Aug. 27th to Sept. 20th the observation were executed almost continuously.

著者

宮崎 務 山口 勝 増谷 文雄 寺尾 弘子

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.51, no.2, pp.115-149, 1976-12-10

著者

Fukao Yoshio

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.48, no.5, pp.707-727, 1970-12-05

---

The focal process of a deep shock which occurred at 580km depth in the Banda Sea region in 1964 is investigated by using long period P and S waves from WWSSN seismograms. The two nodal planes of this earthquake are given by dip direction=319°, dip angle=45°, and dip direction=180°, dip angle=53°, respectively. Assuming that a rectangle represents a far field pulse form, the S wave seismograms are synthesized for various pulse widths and epicentral distances. The effects on the wave form due to passage through the mantle, crust and instrument are removed. Trials are made to find the pulse width, Ts, of the original rectangular pulse which fits the observed S wave form. The variation of Ts with respect to the fault plane orientation is investigated. Ts is remarkably well correlated with the emergence angle measured from the slip vector on the nodal plane with dip direction=319°, dip angle=45°. This result, leads to the following conclusions: (1) The source is plane-like rather than spherical; a fault, model is more preferable to a phase transition model. (2) The nodal plane with dip direction=319° and dip angle=45° is the fault plane. (3) The fault surface is not circular but elongated. (4) The direction of elongation coincides, with the slip direction. (5) The fault width W should not exceed 15km. It may. probably be smaller than 10km. (6) The fault length L is estimated to be 40.km. (7) The process of the body wave radiation took place almost simultaneously, within about two seconds, over the entire fault surface; this model is significantly different from the ordinary propagating fault model. On the basis of this model, the seismic moment M0 is estimated to be 5.8×1026 dyne cm from the P wave amplitude and width. Assuming W=8km, the average dislocation, stress drop and elastic energy released when the fault surfaces become free, are. estimated to be 150 cm, 290 bars and 7.0×1022 ergs, respectively. The stress drop obtained here is one order of magnitude greater than that estimated for shallow earthquakes.|1964年バンダ海で起った深さ580kmの深発地震の震源過程を世界標準地震計観測網が記録した.長周期P波およびS波を用いて調べた.この地震の2つのP波節面はdip direction=319°dip angle=45°およびdip direction=180°, dip angle=53°で与えられる.S波の遠方での波形が矩形で近似できると仮定して種々のパルス巾,震央距離に対してP波理論記象を作った.その際,マントル,地殻および地震計を通過するときの波形への影響を考慮した.これらを実際の記録と比較して,もとの矩形波のパルス巾,Ts,を求めた.Tsの方位に関する著しい規則性より次の結論を得た.(1)震源は球状ではなく面状であり,従って相転移モデルより断層モデルの方が適当である.(2)dip direction=319°,dip angle=45°のP波節面が断層面である.(3)断層面は円ではなく,slip方向にのびた細長いものである.(4)断層の巾は15kmを越えず,恐らく10km以下と思われる.(5)地震は断層面全体にわたって殆ど同時に起ったと考えられる.この間約2秒である.普通の伝播性断層モデルでは結果を説明できない.(6)断層の長さは約40kmである.これらの結論はP波の実際の波形とも矛盾しない.P波理論記象と実際の記録との比較から地震モーメントは5.8×1026dyne cmと推定される.断層の巾を8kmと仮定すると,断層面上でのくい違いの大きさ,stress dropおよび断層面がfreeになったと仮定したとき解放される弾性エネルギーは,それぞれ150cm,290 barsおよび7.0×1022 ergsとなる.

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

東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

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

---

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

萩原 幸男 長沢 工 大久保 修平

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.61, no.3, pp.529-535, 1987-02-10

---

1847年善光寺地震のとき発生した断層は垂直変位をもつので,断層をはさむ両側のブーゲー異常に差が生じている可能性がある.断層によるブーゲー異常の乱れの発見を目的として,長野市街地を中心に84点の重力測定を実施した.しかし結果として,期待されたコンターの乱れは発見されなかった.この地震断層の西側に隣接して,顕著な低ブーゲー異常帯が存在することが判明した.これは断層破砕帯のような待異な構造に関連するものかもしれない.

著者

宇津 徳治

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.63, no.1, pp.23-31, 1988-06-30

---

日本の地震について,震央付近の震度I0(気象庁震度階級),マグニチュードM(気象庁方式),震源の深さh(km)の標準的関係を表す実験式を1114個の震度データを用いて求め,次式を得た.M=0.23 I0+0.105 I02+1.2log h+1.3この式はMが2~8,hがO~100km.I0がO~6の地震を対象としている.ただしh=Oと発表されている地震の実際の深さは数kmと考えて,h<3kmの場合はh=3kmと置く,Mが5程度より大きい地震についてはm=1.2I0+1.21log h-0.83すなわちI0=O.83 M-log h+0.71を用いてもよい.

著者

宇津 徳治

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.57, no.3, pp.401-463, 1983-01-17

---

A catalog of earthquakes of magnitude 6 or more felt in Japan and smaller earthquakes which caused damage in Japan from 1885 through 1980 is presented. The catalog also contains unfelt earthquakes of M≧6 which occurred in the vicinity of Japan (region A indicated in the map), but the listing of unfelt earthquakes may be incomplete for the years before 1924. The catalog is incomplete for deep earthquakes before 1900. The main sources of materials are Utsu's catalog of 1979 (revised in 1982) for 1885-1925, the new JMA catalog (1982) for 1926-1960, and the JMA Seismological Bulletin for 1961-1980. Gutenberg-Richter's catalog (1954), ISS, or ISC Bulletins are used for focal coordinates of earthquakes occurring outside of the network of JMA stations. For some earthquakes the author has determined the focal coordinates or magnitudes. Statistical analyses of the catalog and studies of seismicity patterns in relation to the occurrence of great earthquakes will be published elsewhere.

著者

宇津 徳治

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.59, no.2, pp.219-233, 1984-10-20

---

日本の浅発地震(ただし東日本の太平洋岸沖合を除く)に対する震度I(気象庁震度階級),震央距離Δ(km),マグニチュードM(気象庁方式)の標準的関係を表わす実験式を181個の地震(M:5~8)の震度データを用いて求めた.このような標準式を定めるうえで生ずるいくつかの問題について議論したが,若干の問題は解決が困難で適当に処理せざるを得ない.本論文ではI-Δの平均回帰直線I=I100-b(Δ-100)の定数を,次の式でMと結んだものを標準式として提出する.I100=1.5M-6.5 b=0.0767-0.015M+0.0008M2なお,使用目的によっては本文中に掲げられている別の式を用いるほうが適当な場合もあろう.

著者

宇津 徳治

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.57, no.1, pp.111-117, 1982-07-16

---

On the basis of newly collected data, a revision of the catalog of earthquakes in Japan between 1885 and 1925 (UTSU, 1979) has been made.

著者

Utsu Tokuji

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.59, no.1, pp.53-66, 1984-07-10

---

Four renewal models have been applied to several seismic regions of Japan where large earthquakes occur repeatedly at fairly regular time intervals. The model parameters have been determined by the method of moments and the method of maximum likelihood. The four models represent the distributions of time intervals fairly well, though different models are best suited for different sets of data. The probability of the occurrence of the next large earthquake during a specified interval of time can be calculated easily for each model. Some sample results are presented.

著者

Abe Katsuyuki Kanamori Hiroo

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.48, no.6, pp.1011-1021, 1971-01-30

---

Group velocities of long-period Rayleigh and Love waves are measured, by band-pass filtering and group-delay time methods, to study regional differences in a deep island arc structure. The measurements are made, over a period range 20 to 80 sec, for propagation paths across the Japan Sea. At longer periods, the observed group velocities of Rayleigh and Love waves are lower by as much as 0.1 km/sec than those for normal oceanic paths. It is found that the ARC-1 model, which was previously introduced to explain the low group velocities of long-period surface waves travelling across the Philippine Sea, can also explain these low group velocities. The major feature of this model is a reduction of mantle shear-velocity by 0.3 to 0.4 km/sec, or 8%, over a depth range 30 to 60 km as compared with that for normal oceanic models. This low mantle velocity and the high heat flow which was previously reported for this region suggest common causes such as high temperature and partial melting. The velocity contrast found here can be explained in terms of a 500℃ temperature excess coupled with a 4% partial melting.|長周期表面波の群速度をもちいて,弧状列島の縁海である日本海のマントル構造を調べた.日本北部及び千島列島の5つの地震についてソウルにおける長周期地震計の記録から,バンド・パス・フィルターとグループ・ディレイ・タイム法を利用して周期20秒から80秒までの群速度を求めた.日本海を横切る表面波の群速度は標準的な海のものにくらべ長周期のところでレイレー波ラブ波ともに0.1km/secほど遅い.この遅い群速度は以前にフィリッピン海を横切る表面波の遅い群速度を説明するためにもちいたARC-1モデルで同じように良く説明される.このモデルの重要な特徴は標準的な海のモデルにくらべてマントルの横波の速度が深さ30~60kmにわたって0.3~0.4km/secまたは8%ほど遅くなっていることである.この浅い所における低速度層の存在と日本海での高熱流量とを考えあわせると.日本海の下のマントル内では他の地域にくらべて温度が高く,またそれによって部分溶融が生じていると考えられる.この考えにしたがうと8%の横波の速度差は4%程度の部分溶融をともなった500℃の温度差で説明される.

著者

佃 為成 酒井 要 橋本 信一 羽田 敏夫 小林 勝

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.63, no.3, pp.237-272, 1988-12-23

---

北部フォッサマグナの中央隆起帯を横断する千曲川構造線の東端に位置する長野県小県郡丸子町付近で1986年8月24日,M4.9の地震が発生した.ここは2つの火山前線がぶつかる点のすぐ背後でもある.通常の地震活動レベルは低いが,過去には1912年の上田市付近の地震(M5.2)がある.丸子町の地震活動は前震・本震・余震系列と本震の10日後から始まった群発地震が重なったものであった.2回の主要な活動ピークをもつ例は,北部フォッサマグナ地域では少なくなく,ピーク間の間隔は1918年大町地震の13時間,1969年焼岳の地震の2日,1912年上田の地震の5日,今回の地震の12日,1963年燕岳の地震の20日,1897年上高井の地震の104日というように様々である.2回目が群発地震であったのは丸子の地震と,燕岳の地震,上田の地震である.現地における臨時観測によって精密な震源分布が得られた.震源域は時間とともに拡大したが群発地震後最終的には東西3km,南北2km,深さは6kmを中心に3kmの幅をもつ拡がりであった.定常観測網で求めた震源との比較を行い,観測網に依存する震源の系統的なずれやその値のバラツキから震源の絶対精度と相対精度を推定した.MO~4.5の間のM別頻度分布はGutenberg-Richterの関係から少しずれる.群発地震の回数の減衰(p~2)は本震直後の余震のそれ(p~1)と比べ大きい.燕岳の地震ではどちらもp~2であった.本震の震源断層は発震機構及び余震分布の特性から西上り東落ちの高角逆断層である.これは中央隆起帯東縁でのテクトニックな変動と調和する.1986年の千曲構造線の地震活動はそのピークが東南東から西北西へ約150km/yearの速度で伝播した.1912年~1918年にもこの構造線の両端付近で地震があった.約70年の間隔を置いて同じような活動を繰り返したことになる.

著者

Mogi Kiyoo

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.41, no.3, pp.615-658, 1963-09-30

---

In the preceding papers40', the patterns of the successive occurrence of elastic shocks accompanying fractures under a simple stress state have been experimentally investigated and they have been classified into three types. The type of shock sequence is decidedly influenced by the mechanical structure of model materials. In this paper, this experimental conclusion has been applied to earthquakes in and near Japan (1926-1961). The main results are summarized as follows. (1) The patterns of earthquake sequences are also classified into the three types which were obtained in the patterns of shock sequences, but the transition from one to another is continuous. (2) About 60 earthquakes preceded by foreshocks (the second type)'have been found. They distribute in groups at certain regions. In such regions where the normal sequence of foreshocks is expected, the seismic- observations may give a clue for prediction of major earthquakes. (3) The regions where a certain type of earthquake sequence frequently appears distribute following a general tendency. The various patterns of earthquake sequences are related to the various degrees of heterogeneity in structure. Thus, the spatial distribution of the regions fractured in various degrees are deduced from the data of the patterns of earthquake sequences. (4) The probability P that an earthquake is followed by aftershocks increases with the magnitude and decreases with the focal depth. Furthermore, the P value varies remarkably in various regions. The spatial distribution of the regions having a high P value of aftershock occurrence is nearly identical to that of the second type and the third type. These regions are also the regions which are fractured to some degree. (5) The spatial distribution of fractured regions deduced from the types of the pattern of earthquake sequences has close relations to various geotectonic structures of the Japanese islands, and to other geophysical data.

著者

村井 勇 松田 時彦

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.50, no.3, pp.303-327, 1976-03-31

著者

萩原 幸男 村田 一郎 田島 広一 長沢 工 井筒屋 貞勝 大久保 修平

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.61, no.4, pp.563-586, 1987-03-31

---

埼玉県北西部の関東山地北東縁部には,深谷断層,櫛挽断層,江南断層,今市-菅谷断層等の活断層が密集している.この地帯に7回にわたって合計約630点の重力測定を実施した.得られたブーゲー異常から,地質地形調査ではかつて指摘されたことのない断層を児玉町に発見した.また櫛挽断層は従来考えられていた規模より遙かに大きく,北西にはこの児玉町の断層に,南東には荒川を越えて今市-菅谷断層に連続していることが判明した.1931年西埼玉地震(M7.0)の震源断層は恐らくこの一連の断層と関連があるものと思われる.

著者

羽鳥 徳太郎

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 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.57, no.3, pp.525-535, 1983-01-17

---

A small tsunami was generated by the Urakawa-oki earthquake (M=7.1) near Cape Erimo, southern Hokkaido, on March 21, 1982. At Urakawa, the initial disturbance of the present tsunami began with an upward motion simultaneous with the earthquake occurrence. The first wave period was 16min and the third wave was the highest with a semi-amplitude of 80 cm. According to the author's method based on the attenuation of wave-amplitude with distance, the tsunami magnitude (Imamura-Iida scale) are estimated to be m = 0. This rank is average for an earthquake having a magnitude of M=7.1. The source area of the present tsunami which inferred from an inverse refraction diagram is located along the coast from Urakawa to Shizunai. The length of the tsunami source is 40 km and the width 20 km. The tsunami source area agrees with the aftershock area. From the analysis of the initial tsunami motion on the records, an average uplift of 14 cm may have occurred at the sea-bottom of the source area.