| Project/Area Number |
03554009
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| Research Category |
Grant-in-Aid for Developmental Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | Hokkaido University |
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Principal Investigator |
OKADA Hiroshi Hokkaido University Fac.of Sci., Prof., 理学部, 教授 (40000799)
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| Co-Investigator(Kenkyū-buntansha) |
NAKANO Osamu Dia Consultant Co., Ltd., Head of Expl.Section, 技術研究所, 課長
SASATANI Tsutomu Hokkaido University Fac.of Sci., Instructor, 理学部, 講師 (10002148)
MORIYA Takeo Hokkaido University Fac.of Sci., Ass.Prof., 理学部, 助教授 (60001864)
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| Project Period (FY) |
1991 – 1993
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| Project Status |
Completed (Fiscal Year 1993)
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| Budget Amount *help |
¥12,400,000 (Direct Cost: ¥12,400,000)
Fiscal Year 1993: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1992: ¥4,100,000 (Direct Cost: ¥4,100,000)
Fiscal Year 1991: ¥7,100,000 (Direct Cost: ¥7,100,000)
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| Keywords | Exploration technique / Microtremors / Surface waves / Phase velocity / F-K spectrum / AR model / Spatial autocorrelation / ラブ波 / 構造探査 / 表面波 / 周波数:波数スペクトル / 周波数ー波数スペクトル / 地下構造 / 周波数一波数スペクトル / レイリ-波 |
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| Research Abstract |
A new exploration technique using microtremors with periods longer than 1s has been developed for estimating geological structure to a depth of about 3, 000m. Since microtremors can be observed at any time in any place, the technique makes it possible to cover a given area more easily, quikly, and economically than any other seismic techniques. The technique is, therefore, useful for reconnaissance survey in areas to be newly explored, and also alternative to the conventional seismic techniques especially in urban areas. The microtremor is essentially a random ensemble of body and surface waves, so that the microtremor we observe is very complex in waveform in which, however, the surface waves must be inevitably more predominant in power. The present technique utilizes the dispersion characteristics of the surface waves in such microtremors. The research mainly deals with measurement of phase velocities of surface waves in microtremors, for which data acquisition and processing have be
… More
en developed. The data acquisition is made by such an array observation system that the data are simultaneously collected for which the observation points of an array consisting of 10 seismometers are isolated from each other. With high-precision coded quartz crystal clocks, the data are recorded separately and correlated at the time of processing. Since the system does not require cable or radio transmission, a great flexibility is attained in array design. The seismometer used is the portable 3-component seismometer UP255 (Shindo Giken Co., Ltd.), its natural period being reset from 1s to 8s.
For the data processing, the traditionally used frequency-wavenumber spectrum (F-K spectrum) analysis is improved by introducing a new AR-modeling algorithm into calculation of cross-spectrums, and the spatial autocorrelation method efficient to detection of surface waves from complex wave train is extended to a higher form in arrangement of seismometer array.
The new technique examined about more than 30 array measurements provided successful estimation of the phase velocity of the fundamental mode of Rayleigh waves with high accuracy. Less
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