Vs Soil Profile Estimated from Inverse Analysis of Observed Rayleigh-wave Dispersion Characteristics

The possible limitations and/or potentials of Vs soil profiles estimated from inverse analysis of observed Rayleigh-wave dispersion characteristics of microtremor records at 4 sites in Akita prefecture (Japan) are discussed. Available borehole records of these sites were used for comparison purposes. Seven vertical component microtremor records arranged in triangular array were measured at each site. The Rayleigh-wave dispersion characteristics were estimated after using the high resolution f-k spectral method. Random inverse analysis using the Rayleigh-wave dispersion characteristics was performed assuming a ground model of six layers overlying a half-space. Ten millions of random ground models were tested at each site. According to results, two conclusions could be given. First, the Vs soil profiles for S-wave velocities lower than the value of the fastest observed Rayleigh-wave velocity agreed well with borehole records. Second, the Vs soil profiles for S-wave velocities faster than the value of the fastest observed Rayleigh-wave velocity showed larger variations when comparing with borehole records. Due to the limitations of Rayleigh-waves to be propagated through these consolidated layers, S-wave velocity and thickness of deeper consolidated layers using observed passive Rayleigh-wave dispersion characteristics would be difficult to be estimated.