Effect of trigger system on experimental dispersion characteristics of active surface wave testing

A trigger system is typically employed in active seismic testing to trigger and synchronize multichannel surface wave data acquisition. The effect of the trigger system on the dispersion image of surface waves is empirically known to be negligible, however, theoretical explanation regarding the effect of the trigger system is insufficient. This study systematically examines the theory for surface wave dispersion analysis and proves that the effect of the trigger system on a dispersion image is negligible via a solid theoretical explanation. Subsequently, based on the new theoretical explanation, an alternative method that uses only the relative phase difference between sensors to extract dispersion characteristics with better conceptual clarity is proposed. Two active surface wave testing cases are considered to validate the theory and method. The results indicate that (1) an accurate trigger system is not necessary for surface wave data acquisition, and (2) it is unnecessary to assume that the impact point is the generation point of the surface waves for the experimental dispersion analysis.