Seismic Refraction

Seismic refraction is a geophysical technique used to interpret depth and layer velocities of soil, partially weathered rock, and competent rock. Layer velocities are important because they directly correlate with the material's hardness and/or amount of fracturing. This is particularly useful in determining excavation equipment and techniques for rock removal or subsurface mapping of bedrock.

Because seismic refraction is noninvasive with no need for vehicle or motorized equipment access, it has proven to be a popular choice for professionals working in:

Real Estate
Developing
Construction
Excavation
Environmental

From a densely wooded property to an active city street, seismic refraction is a versatile technique used for characterizing the subsurface.

GeoWave Solutions, Inc.'s seismic refraction surveys consist of data that are collected using two-dimensional receiver arrays and a compression source (usually a sledgehammer). By positioning the source at multiple locations along the array and collecting first-arrival information from the receivers, a two-dimensional subsurface profile based on subsurface compression wave velocities can be generated.

The depth of investigation is based on source to receiver distances, the overall length of the receiver array, and surrounding ambient noise. Based on a 10-foot geophone receiver spacing, typical survey depths average approximately 35 to 40 feet deep for 12-channel receiver arrays and 70 to 80 feet deep for 24-channel arrays. Although, under the right conditions, deeper investigations can be conducted by increasing the number of source locations beyond the extent of the receiver array.

The raw data collected from the field are reduced into velocity models, which were the basis for the final seismic profiles. We conduct tomographic processing on each data set which provides a subsurface velocity model that shows subtle vertical and horizontal changes in the underlying soil and rock. The tomographic results on the final models consist of the color contour data representing measured compression wave velocity. These data were used to annotate a geologic interpretation on each model by delineating subsurface layers where compression wave velocities change.