1997 Fiscal Year Final Research Report Summary
DEVELOPMENT OF REAL-TIME GEOPHYSICAL EXPLORATION SYSTEM BASED ON ARRAY OBSERVATION OF THREE-COMPONENT MICROTREMORS
| Project/Area Number |
08555140
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
Building structures/materials
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| Research Institution | TOKYO INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
TOKIMATSU Kohji TOKYO INSTITUTE OF TECHNOLOGY,Professor, Faculty of Engineering, Tokyo Institute of Technology, 工学部, 教授 (50134846)
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| Co-Investigator(Kenkyū-buntansha) |
ARAI Hiroshi JSPS Research Fellow & Graduate Student, Graduate School of Science and Engineer, 大学院・理工学研究科, 特別研究員
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| Project Period (FY) |
1996 – 1997
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| Keywords | Microtremors / Array observation / Surface waves / Rayleigh waves / Love waves / Shear wave profile / Amplification / F-k spectrum analysis |
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| Research Abstract |
Field techniques and analytical procedures have been presented for geotechnical site characterization using microtremor three-component ground motions, in addition to their applicability for evaluating spatial variation of soil profiles and ground motion characteristics. The present system can readily provide Rayleigh- and Love-wave dispersion curves as well as H/V spectra from spectrum analyzes of microtremor three-component ground motions. The dispersion curves and H/V spectra of surface waves have been theoretically derived in which the effects of higher-modes can be taken into account. Inverse analyzes using both Rayleigh-wave dispersion curve and Love-wave dispersion curve or H/V spectra have been presented for determining shear wave velocity profiles.
It is shown that :
(1) The theoretical dispersion curve of Rayleigh waves shows a good agreement with those determined by te F-k spectrum analysis of the microtremor vertical motions in any case.
(2) The theoretical dispersion curve of
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Love waves shows a good agreement with those determined by the F-k spectrum analysis of the microtremor transverse horizontal motions, if microtremors propagate from one direction.
(3) The proposed H/V spectrum of surface waves shows a good agreement with observed microtremor H/V spectrum, claiming its validity.
(4) The proposed inversion process using both Rayleigh-wave dispersion curve and Love-wave dispersion curve or H/V spectra can yield more reliable shear wave velocity profiles than that using Rayleigh-wave dispersion curve only.
To demonstrate the effectiveness of the proposed methods, microtremor measurements using arrays are conducted in Kushiro and Kobe and the shear structures in those areas are estimated down to depths of about 50 m and 1.5 km, respectively. The estimated shear structures are in good agreement with those determined by the conventional methods, indicating the effectiveness of the proposed method. Effective stress response analysis is then made using the estimated soil profiles. The computed distribution of the peak ground velocity and acceleration as well as the transfer funcion between stations are consistent with those observed during the earthquakes, suggesting that the proposed methods are promising. Less
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