Estimation of Vs soil structures from microtremor measurements and its verification by synthetic microtremor array

本研究试图验证层状土壤结构（Vs土壤剖面）估算的可能性和局限性。利用从观测到的和合成的微震得到的瑞利波色散特性。在秋田县19个KiK-net地震观测点，利用7个三角阵站点进行了微震测量。利用f-k谱法获得了各点的瑞利波色散特性。利用蒙特卡罗方法进行反演分析，估计了可能的Vs土壤剖面，并与现有的PS测井记录进行了比较。与PS测井记录相比，估算的Vs土壤剖面显示，s波速度的散射比观测到的最快瑞利波相速度慢，s波速度的散射比观测到的最快瑞利波相速度快。f-k谱法得到的相速度值大都小于1000 m/s，表明土壤Vs的估算值较低。松散土层的剖面是可能的。为了从观测到的微震动中验证上述趋势，我们计算了6个地面系统中7个三角形阵虚拟台站的合成微震动，这些系统由地面增加的层数组成。第一个地面系统由第一个上层覆盖随后的第二层组成，在这个地面系统中被认为是半空间；以此类推，直至第6层地面系统，该系统由6层组成，覆盖在横波速度为2500m /s的半空间上。将f-k谱法应用于模拟微震对应的7个虚拟垂直分量，得到了6个地面系统的合成瑞利波频散曲线。不同地面系统的瑞利波频散曲线差异不大。此外，当s波速度比逆分析中使用的最快瑞利波相速度快时，估计的v -土结构具有较大的散射。综上所述，瑞利波的传播可以从较深的某一层进行抑制。少

This research attempts to verify the possibilities and the limitations of estimating layered soil structure (Vs soil profile). by using Rayleigh-wave dispersion characteristics obtained from observed and synthetic microtremors.Microtremor measurements using 7 stations in triangular array were performed at 19 KiK-net seismological observation sites in Akita Prefecture. The Rayleigh-wave dispersion characteristics at each site were obtained by applying the f-k spectral method. By using the Monte Carlo method for inverse analysis, the possible Vs soil profiles were estimated and compared with the available PS well log records. The estimated Vs soil profiles when comparing with PS well log record showed low scattering for S-wave velocities slower than the fastest observed Rayleigh-wave phase velocity, and showed large scattering for S-wave velocities faster than the fastest observed Rayleigh-wave phase velocity. Most of values for phase velocities obtained by the f-k spectral method were l … More ower than 1000 m/s, meaning that the estimation of Vs soil. profile of unconsolidated soil layers is possible.To verify the above mentioned tendencies from observed microtremors, synthetic microtremors at 7 fictitious stations in triangular array were computed for 6 ground systems, which consisted of increasing number of layers from the surface ground. The 1st ground system consisted of the first upper layer overlying the subsequent second layer, considered in this ground system as half-space ; and so on, up to the 6th ground system, consisting of 6 layers overlying a half-space whose S-wave velocity is 2500 m/s.The synthetic Rayleigh-wave dispersion curve at each of the 6 ground systems were obtained after applying the f-k spectral method in their corresponding 7 fictitious vertical components of simulated microtremors. Little differences between Rayleigh-wave dispersion curves from a specific ground system were obtained. Also, large scattering for estimated Vs-soil structures were obtained for S-wave velocities faster than the fastest Rayleigh-wave phase velocity used in inverse analysis. In conclusion, the propagation of Rayleigh-waves could be restrained from a certain deeper layer. Less