Some Recent and Emerging Topics on Seismic Wave Methods for Geotechnical Site Characterization

Abstract

New developments in surface-based seismic wave methods are described around three significant themes: 1) array signal processing, 2) numerical methods for solving the equations of wave propagation, and 3) global optimization methods for solving the inverse problem. These themes are illustrated via examples from surface wave, refraction-based travel time, and full waveform inversion techniques. Based on concepts from array signal processing, inversion of the combined dispersion curve from a non-uniform active-source surface wave array and a 2D passive-source array yielded a significantly deeper shear wave velocity profile for a site in Florida than produced using dispersion data from a sledgehammer source uniform array and ReMi. A new technique is presented to invert refraction-type first-arrival times using the multistencils fast marching method finite-difference solution of the Eikonal equation and simulated annealing global optimization. A comparison of inversion results utilizing the new technique to analyze data collected simultaneously within a borehole and along the ground surface against inversion results developed using just the surface data suggests that significant additional resolution of inverted profiles at depth are obtained, and uncertainties are significantly reduced with the addition of a borehole. Lastly, techniques are presented to invert full waveforms using two global optimization methods, a genetic algorithm and simulated annealing. The inversion scheme is based on a finite-difference solution of the 2D elastic wave equation in the time-distance domain. It is demonstrated that these inversion techniques are capable of characterizing both lowand high-velocity layers in laterally inhomogeneous profiles, and that full waveform inversion is computationally practical.