Seismic Refraction Survey

The seismic refraction method is based on the measurement of the travel time of seismic waves refracted at the interfaces between subsurface layers of different velocity. Seismic energy is provided by a source located on the surface. Energy radiates out from the shot point, either travelling directly through the upper layer (direct arrivals), or travelling down to and then laterally along higher velocity layers as refracted arrivals before returning to the surface. This energy is detected on the surface using a linear array of geophones. Observation of the travel-times of the refracted signals provides information on the depth profile of the refractor.

If external constraints are available, the velocity–depth profile can be transformed into a geological model. The conversion of observed travel times can be carried out using a number of techniques. In simple geological scenarios where fast turn-around of results is a required, a time-intercept approach can be used. For cases with suspected significant lateral heterogeneity the, tomographic inversion approach is recommended.