GeoWave Solutions, Inc.
4575 Ansley Lane, Cumming, Georgia 30040
Office: 770-886-3776 Fax: 770-886-7212
A seismic refraction array parallel to a busy road
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:
From a densely wooded property to an active city street, seismic refraction is a versatile technique used for characterizing the subsurface.
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.
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.
Compression wave being generated by a sledgehammer
Seismic tomography is another means by which GeoWave Solutions, Inc. can process and display seismic refraction results. While the layer-based method shows distinct strata boundaries at depth, the tomographic method uses contouring to show gradational transitioning between layers. This type of seismic processing is better able to model lateral changes of seismic velocities because no assumptions are made about the lateral continuity of the layer velocities. When modeling a highly irregular bedrock surface or modeling subsurface conditions that gradually increase in density with depth, seismic tomography will likely be the most accurate processing method.
Layer-based seismic refraction processing is the most common technique for interpreting seismic results. It uses absolute layer interfaces with layer velocities to show subsurface conditions which are helpful when quantifying rock. Layer-based seismic processing is typically best for bedrock rippability studies and most other conditions where partially weathered rock or competent rock have definable interfaces.
The two profiles on the left illustrate the difference between the tomographic and the layer-based processing methods. Both profiles were processed using the same 12-channel data.
A. Tomographic seismic refraction profile of data set.
B. Layer-based seismic refraction profile of data set.
By combining these two methods, a more robust and accurate seismic model is achieved. This new model has the layer-based advantage of quantifiable rock, and, at the same time, the tomographic advantages of depicting gradational boundary transitions and lateral velocity variances that are common in most geologic provinces.