- 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
- 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
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
- 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.