An improved method for the identification and inversion of multi-mode Rayleigh surface wave dispersion collected from non-uniform arrays utilizing a moving source approach

An improved method using a moving source approach is utilized in the analysis of Rayleigh surface waves for the accurate identification of higher mode propagation used in inversion. Two non invasive surface wave methods, Multi- station Analysis of Surface Waves (MASW) and Refraction Microtremor (ReMi) were used for the construction of composite dispersion curves representing the relationship of Rayleigh phase velocity (VR) with frequency. Multiple tests were executed with source offsets increasing with each successive test in order to account for near field effects and higher mode attenuation levels. The resulting dispersions were combined to form a composite dispersion which effectively maps all participating modes of propagation. The inversion was executed using a genetic algorithm (GA) which takes advantage of the Rayleigh forward problem. The results show good ability to identify intermediate high and low velocity layers and agree well with downhole results.