An overview of surface wave methods and a reliability study of a simplified inversion technique

Following a brief overview of the history and the development of the Surface Wave Method—with a focus on techniques for processing and inverting field data—a Simplified Inversion Method (SIM) is described, which constitutes an improvement of the Satoh et al. (1991) [1] method. The SIM is a direct inversion method of surface wave dispersion data, making use of a penetration depth coefficient, aR, whose value is a function of Poisson's ratio and the overall shape of the dispersion curve. In the present study the coefficient aR has been evaluated using data from (a) an extensive database compiled from the technical literature and containing results of inverted surface wave measurements and nearby cross-hole/down-hole measurements, (b) results of side by side surface wave and cross-hole measurements, performed at five sites in the course of this study, (c) finite element analyses simulating the performance of surface wave measurements and thus providing “virtual” data, and (d) applying a current advanced inversion code, available on the Web. Based on all the above data, optimum values of aR (and of the corresponding uncertainty of the derived Vso vs. depth profile) have been estimated. These values were found to be independent of depth from ground surface. The results of all analyses and comparisons indicate that for the majority of realistic soil profiles (including cases of normal and inverse dispersion conditions) the proposed SIM provides very reliable Vso vs. depth profiles when a value of aR=0.63–0.67 is used in the inversion process. It is concluded that the SIM can be used with confidence as a direct inversion method of surface wave dispersion data.

► A reliable and direct Simplified Inversion Method (SIM) is proposed. ► SIM makes use of a penetration depth coefficient, aR. ► Value of aR is optimized using a large database of field measurements.