Investigation of Near-surface Anomalies Using the Refraction Seismic Method

In this paper we investigate the influence of near-surface anomalies on the first arrivals of seismic waves. The basic two-layer model is modified with the following anomalies: (1) circular cavity positioned in the upper layer, (2) buried circular object positioned in the upper layer, (3) part of the border between the layers is deformed into concave shape. All anomalies are characterized with the seismic velocities that are lower than the seismic velocity of the neighboring region. First arrivals are calculated by numerical modeling of 2D eikonal equation. Numerically obtained traveltimes are presented in the time-distance graph and are also used to construct the graph of wavefronts. In all cases, the shape of the time-distance graph is characterized by a peak point which is a consequence of slower propagation of seismic waves through the analyzed anomalies.