Effectiveness of group velocity analysis of surface waves for near surface characterization

In earthquake seismology, group velocity of surface waves is widely used to infer the interior structure of the Earth. Robust techniques exist to compute the group velocity spectrum, also for single trace data. This feature, when applied to shallow shear-wave characterization, seems to be very appealing to practitioners for reducing field operations. The main problem concerning the application of group velocity measurements to active seismograms for shallow targets is the interference between the modes, especially at short offsets. The main objective of this work is to analyse the potential of group velocity dispersion for near surface characterization, with particular focus on signal discrimination, sensitivity with respect to the soil structure and possible sources of interpretation pitfalls. Our analysis demonstrate that the sensitivities and the depth of penetration of group velocity data are almost similar to phase velocity ones. Consequently, when the dispersion analysis is based on active multichannel arrays, group velocity does not add much information to the inversion process. On the other hand, the possibility of using single station measurements has a great value in all those situations when data are fundamental-mode dominated or the deployment of large arrays is not feasible, such as in urban areas.