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

本研究试图验证估算分层土壤结构(VS土壤剖面)的可能性和局限性。利用观测微震和合成微震的瑞利波频散特性，对秋田县19个Kik-Net地震观测点进行了7个台站的三角阵地脉动测量。应用f-k谱方法得到了各测点的瑞雷波频散特性。利用蒙特卡罗方法进行反分析，估算了可能的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土壤剖面对S波速度慢于最快观测瑞雷波相速度显示出低散射，对S波速度快于最快观测瑞雷波相速度显示出大散射。由f-k谱方法得到的相速度值大多是L…。高于1000m/S，这意味着对土壤的估计。为了从观测到的脉动中验证上述趋势，计算了6个地面系统的7个虚拟台站的合成脉动，这些系统从地表开始增加了层数。第一地面系统由第一上层覆盖第二层，在本地面系统中被视为半空间，依此类推，直到第六地面系统，由覆盖S波速为2500m/s的半空间上的6层组成。对相应的7个模拟地震动的虚拟垂直分量应用f-k谱方法，得到6个地面系统的合成瑞雷波频散曲线。不同地面系统的瑞雷波频散曲线差别不大。此外，当S波的速度快于反分析中使用的最快瑞利波相速度时，估计的V-土结构也获得了大的散射。综上所述，瑞雷波的传播可以从一定的深层进行抑制。较少

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