propagation to identify near Effect of subsurface cavity length on Rayleigh wave and far boundary of the cavity

Subsurface identification in some cases requires seismic testing, especially when the goal is to identify anomalies at the site. Identifying and determining the dimensions of these anomalies is important because these cavities may be of considerable size and close to the ground. And cause irreversible risks by applying loading or any other changes in the soil environment. Seismic methods can also be used to identify aqueducts, mineral, oil and gas exploration. Due to various methods of identifying subsurface anomalies, in this paper, the multi-station surface wave analysis method is used, which is very fast and cost-effective. In this regard, by simulating in Abacus, finite element software environment, the effect of longitudinal dimensions of shallow subsurface cavities has been evaluated. The cavities are located at different lengths below the ground and the waves field in the time-offset and dispersion curves and graphs in the frequency-offset after the filter are examined. The obtained results in the time-distance showed that for a cavity with a length of 2, 4, 6 and 8 meters, the scattered waves are emitted from the far and near the face of the cavity with a longer time distance from each other in proportion to the increase in the length of the cavity. It can be concluded that the near and far boundary of cavity could be determined by using high resolution obtained data after filtering in time-distance domain, and more energy data in frequency-distance domain.