Spotlight Geophysical Services services

A gravity survey measures changes in the Earth’s gravity due to subsurface density variations.Microgravity is a term used to indicate a precision gravity survey in which near surface features are of interest. These features may include lateral changes in soil or rock density, buried channels, large fractures, faults, dissolution-enlarged joints and cavities. A microgravity survey can be used to map the lateral boundaries of anomalous features, estimate the amount of missing mass within an anomalous area, and guide confirmatory borings.

Seismic refraction is a geophysical method used to determine the seismic compression-wave (P-wave) velocity structure of the subsurface. Seismic P-waves are generated on the surface, propagate through the soil and rock, and are recorded by geophones at known distances from the source. Since P-waves are the fastest portion of the seismic wave, they represent the first arriving energy at each geophone (either direct or refracted). A seismograph is used to record the travel-times of the first arriving energy, after which subsurface seismic P-wave velocities can be derived. A tomographic inversion is used to develop a 2D P-wave velocity cross-section from the data. Seismic refraction data may be acquired on land or in water covered areas.

Marine seismic refraction is a method to determine the seismic P-wave velocity structure of the subsurface. The P-wave velocity is related to the hardness of the sub-bottom materials and can be used to map the top-of-rock, determine the dredgeability of sub-bottom materials, and identify anomalous conditions. Seismic P-waves are generated by a powerful airgun in the water column and propagate through the water and sub-bottom strata. Refracted P-waves are sensed by a hydrophone streamer and recorded by a seismograph. The data are processed to produce a continuous P-wave velocity cross-section, from which geologic interpretations and mapping are developed.