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

本研究试图验证分层土壤结构（Vs土壤剖面）估计的可能性和局限性。利用观测到的和人工合成的地脉动的瑞利波频散特性，对秋田县19个KiK地震台网测点的地脉动进行了三角形排列的7个台站的观测。应用f-k谱方法得到了各测点的瑞利波频散特性。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。当与PS测井记录比较时，估计的Vs土壤剖面显示，S波速度慢于最快观测到的瑞利波相速度时散射较小，而S波速度快于最快观测到的瑞利波相速度时散射较大。用f-k谱方法得到的相速度值大部分为l 关于我们 低于1000 m/s，这意味着Vs土壤的估计。为了验证上述趋势，我们计算了6个地面系统的7个虚拟测站的合成地震动，这些地面系统由地面的层数增加而成。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视为半空间;以此类推，直到第六个地面系统，由6层组成，覆盖在S波速度为2500 m/s的半空间上。在应用f-k谱方法在相应的7个虚拟垂直分量中的应用。从一个特定的地面系统的瑞利波频散曲线之间的差异很小。此外，大散射估计Vs-土壤结构获得的S波速度快于最快的瑞利波相速度在逆分析中使用。由此可见，瑞利波的传播在一定的深度范围内是可以被抑制的。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