| Project/Area Number |
03041024
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Field Research |
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| Research Institution | Earthquake Research lnstitute, University of Tokyo |
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Principal Investigator |
YUKUTAKE Takeshi Professor, E.R.I Univ. of Tokyo, 教授 (90012898)
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| Co-Investigator(Kenkyū-buntansha) |
J HILDEBRAND カリフォルニア大, 助教授
C COX カリフォルニア大, 教授
G.M PURDY ウッズホール海洋研, 教授
R BUTLER IRIS地震学研, 室長
A CHAVE ウッズホール海洋研, 副研究員
UYESHIMA Makoto Assistant, E.R.I Univ. of Tokyo, 助手 (70242154)
C HELSLEY ハワイ大地球物理研, 所長
SATO Toshinori Assistant, E.R.I Univ. of Tokyo, 助手 (70222015)
KINOSHITA Hajimu Professor, E.R.I Univ. of Tokyo, 教授 (10110347)
SHIMAZAKI Kunihiko Professor, E.R.I Univ. of Tokyo, 教授 (50012951)
TANAKA Toshikazu Assistant, Faculty of Science Univ. of Kyoto, 助手 (00025420)
KORESAWA Sadayuki Assistant, E.R.I Univ. of Tokyo, 助手 (80012946)
YUMOTO Kiyofumi Associate Professor, Solar & Earth Environment l, Univ. of Nagoya, 助教授 (20125686)
KATAO Hiroshi Assistant, D.P.R.I Univ. kyoto, 助手 (80221878)
HAMANO Yozo Professor, Faculty of science Univ. of Tokyo, 教授 (90011709)
UTADA Hisashi Associate Professor, E.R.I Univ. of Tokyo, 助教授 (70134632)
KASAHARA Junzo Professor, E.R.I Univ. of Tokyo, 教授 (70012953)
HILDEBRAND J Associate Professor, Univ. of California
PURDY G Professor, Woods Hole Ocean. lnst.
HALSLEY C Hawaii lnstitute of Geophysics, Univ. of Hawaii
BUTLER R IRIS
CHAVE A Woods Hole Ocean. lnst.
COX C Professor, Univ. of California
SHULTZ A. ケンブリッジ大学, 教授
COX C. カリフォルニア大学, スクリップス海洋研究所, 教授
PURDY G.M. WHOI ウッズホール海洋研究所, 教授
BUTLER R. IRIS, 地震学研究室, 室長
CHAVE A. WHOI, ウッズホール海洋研究所, 教授
HELSLEY C. ハワイ大学, 地球物理研究所, 所長
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| Project Period (FY) |
1991 – 1992
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| Project Status |
Completed (Fiscal Year 1992)
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| Budget Amount *help |
¥15,000,000 (Direct Cost: ¥15,000,000)
Fiscal Year 1992: ¥6,000,000 (Direct Cost: ¥6,000,000)
Fiscal Year 1991: ¥9,000,000 (Direct Cost: ¥9,000,000)
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| Keywords | Submarine cable reuse / MT method / Electrical conductivity / Mariana Trough / Seismicity / Seismic noise / Deep ocean / OBS / 海底ケ-ブル利用 / 地電位差変化 / 地磁気変化 / マリアナ諸島 / 海底地震観測 / 光磁気ディスク地震観測システム |
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| Research Abstract |
This research is a basic research to promote a geophysical study in the western Pacific region using GeO-TOC cable which lies between Japan and Guam. There are two major objectives. The first one is to investigate electricalconductivity of the earth by the measurements of voltage change appearing two ends of the cable. The second one is to investigate seismic activity nearly parallel to the cable.
For the first objective, we conducted the following measurements. We separated high frequency signals from the high DC voltage and grounded the DC voltage at Ninomiya station. We measured the voltage change at Guam during the shutdown of power supply to the cable(cold case). After 8 hour measurements, we begun to supply the DC voltage to the cable. We have continued to measure the voltage change(hot case). During the cold measurement, the voltage change showed high similarity to the horizontal component of magnetic filed at Kakioka, Japan and the high S/N values. This high S/N is brought by lo
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ngspan antenna for the measurement of the induced-electrical field of the earth. However, the hot case are interfered by various effects, such as temperature change and the drift of constant current supply unit. By addition of temperature measurement, we suppressed the temperature effect. Applying the MT method, we obtained the electrical conductivity distribution down to200 km in depth. The present results show more similarity to the backarc type than island arc type by the measurements of the Scripps's Institute We are continuing the measurement to obtain deeper structure than 200 km. We are ready to measure the electrical field in the E-W direction using the cable between Guam and Philippine.
Three major researches were done for seismic observation. a) natural earthquakes, crustal structure, detail bathymetric surveies in the Mariana Trough at 18ﾟN, b) broadband seismic observations in Guam, Saipan and Honolulu using accelerometers, and c) seismic noise spectrum in the oceans along the cable. Many normal faults were found in Mariana trough. The strikes of these normal faults are parallel to the Trough axis. The topography is resemble to the MAR. In the Trough, more than 30 microearthquakes were observed in a day. The seismicity at the thermal vent area of the Trough was low. One of the key factors for the cable OBS is seismic noise spectrum at the ocean floor. We analyzed noise spectrum over the period of 0.01-30 Hz band. The quietest period is 0.03-0.1 Hz and the noisiest period is approximately 0.3 Hz. Various factors such as typhoon raised the power failure in islands of Guam and Saipan. And human activities such as rock blasting, tractor made mis-triggering of the instruments. Numerous microearthquakes were observed near Saipan and Guam, but very few earthquakes were observed in Honolulu. However, the station could not observed the volcanic activity near Pagan island. Less
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