Mapping Dispersion Misfit and Uncertainty in Vs Profiles to Variability in Site Response Estimates

AbstractUncertainty in site response analyses can be attributed to a number of parameters, including analysis methods, input ground motions, nonlinear dynamic soil properties, and shear-wave velocity profiles. In this paper, several approaches commonly used to account for shear-wave velocity (Vs) uncertainty in site response are investigated. Specifically, the Vs profiles considered are categorized into three groups: (1) Vs profiles determined directly from surface-wave inversion, (2) simple statistical Vs profiles derived indirectly from the surface-wave Vs profiles (including bounding-type, median, and other percentile Vs profiles), and (3) statistically based, randomly generated Vs profiles. A companion paper discusses the development of these Vs profiles for two international blind-study sites. In this paper, the effects of using each approach to account for Vs uncertainty in site response are investigated by linking the dispersion misfit values for each Vs profile to variability in equivalent linear site response estimates. Clear trends exist between variability in site response estimates and dispersion misfit values at both sites. Thus, the experimental dispersion data can be used to help select suites of Vs profiles, generated either directly from inversion or through a randomization model, that account for uncertainty in a meaningful way without including unrealistic statistical profiles that result in too much site response variability.