DEVELOPMENT OF REAL-TIME GEOPHYSICAL EXPLORATION SYSTEM BASED ON ARRAY OBSERVATION OF THREE-COMPONENT MICROTREMORS

介绍了利用微震三分量地震动表征岩土场地的现场技术和分析方法，以及它们在评估土壤剖面和地面运动特征的空间变异性方面的适用性。该系统可以方便地提供瑞利波和乐夫波频散曲线，以及由微震三分量地震动频谱分析得到的H/V谱。从理论上推导了表面波的色散曲线和H/V谱，其中可以考虑高阶模式的影响。利用瑞雷波频散曲线和勒夫波频散曲线或H/V谱进行了反分析，以确定横波速度剖面。结果表明：(1)瑞雷波的理论频散曲线在任何情况下都与微震垂直运动的TE F-k谱分析所测得的结果吻合良好。(2)…的理论频散曲线如果微震从一个方向传播，则更多的Love波与由微震横向水平运动的F-k谱分析确定的结果吻合得很好。(3)所提出的面波H/V谱与观测到的微震H/V谱具有很好的一致性，证明了其有效性。(4)利用瑞雷波频散曲线和Love波频散曲线或H/V谱的方法可以得到比仅使用瑞利波频散曲线更可靠的横波速度剖面。为了验证所提方法的有效性，利用阵列进行的微震测量在久路和神户进行，这两个地区的剪切构造估计分别深至约50米和1.5公里。计算得到的剪力结构与常规方法确定的剪力结构吻合较好，说明了该方法的有效性。然后利用估算的土体剖面进行有效应力响应分析。计算得到的峰值速度和加速度分布以及台站间的传递函数与地震时的观测结果基本一致，表明该方法是有应用前景的。较少

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 … More 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