Uncertainties in Site Characterization Using Surface Wave Techniques and Their Effects on Seismic Ground Response

Surface wave methods which utilize the dispersion property of Rayleigh waves are widely used for subsurface site characterization. As a non-invasive method of site characterization, it has many advantages over the invasive methods of geotechnical site characterization. Surface wave methods determine the small strain shear modulus of near-surface materials, and this shear modulus is the key input in the evaluation of the soil response under dynamic/seismic loading. So, the accuracy of testing is very important, otherwise it may lead to significant consequences on the seismic hazard studies. There are different uncertainties associated with surface wave methods. These uncertainties can be broadly classified into three categories: Model-based uncertainty, Data measurement uncertainty, and Inversion uncertainty. Model-based uncertainty basically contains the near-field effects which lead to the underestimation of Rayleigh wave phase velocity. Data measurement uncertainty is another major source of uncertainty, which arises while conducting the surface wave tests due to the noise present in the surroundings in the form of continuous or transient signals. Noise results in a scatter in the measured dispersion curve and this scatter in the dispersion curve may provide different velocity profiles, which are falling in the range of measured data variation. Inversion uncertainty deals with non-unique solution of inversion. Non-unique solution may results into several equivalent velocity profiles, with a good fit with the experimental dispersion curve. Now, the consequence of this data measurement and inversion uncertainty may show significant variation on ground response analysis.