Seismic Refraction Surveys Services

Applicability
The seismic refraction technique allows for rapid site reconnaissance, data collection, and “in-house” data analysis. Data can be acquired throughout the site with minimal hand clearing in the areas where data is to be collected.

Procedures
The provided diagram is an example geologic-cross section produced by the RimrockÓ Software Program. To accurately interpret the subsurface conditions, three sound source areas must be established (forward, center and reverse shots). The letters A, B and C on the ground surface indicates these three shot points. A total of 12 geophones is present on this cross-section and is represented with squares on the ground surface. Our seismic refraction process utilizes the elastic body waves (compression waves) generated by a sledgehammer blow at the surface (at the three shot points). These waves pass outward as ever expanding hemispheres through the underlying horizons. That portion of the seismic energy, which passes downward, is bent or refracted at each change of density below the alignment and returns to the surface. The time required for these waves to pass downward, refract and return to the surface is recorded at the surface by the vibration sensitive geophones. Data concerning the arrival times is compiled in the field and converted into characteristic material velocities, expressed in feet per second (fps). Additional calculations are performed to determine depths at which these materials (or horizons) occur below the geophone/source alignment. The seismic process is limited in some respects. The primary one is that if a layer of lower velocity (softer) material underlies a higher velocity (harder) material, the softer material will not be detected. In addition, seismic refraction can reflect groundwater as a high velocity zone. The depth of investigation using the seismic refraction process is roughly equal to one-third the length of each individual seismic spread. Borings and/or test pits are often used in conjunction with seismic refraction to offset these limitations.