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Additional Information
Applications
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Cross-Hole and Downhole Seismic
Borehole seismic surveys are used primarily to help determine in-situ dynamic soil properties and elastic moduli of geologic formations as part of geotechnical studies and for accurate (direct path) calibration of travel-times for surface seismic reflection/refraction surveys. In recent years, seismic wave velocity methods (surface and downhole) have become quite common as an integral part of estimating various geotechnical properties of the subsurface, such as Poisson's ratio and the shear modulus. In fact, the most common method of measuring these properties in engineering studies is through the use of crosshole seismic surveys.
 An important enhancement to seismic refection is the tomographic inversion of first-arrival times obtained from surface seismic profiles or recordings between boreholes to form 2-D and 3-D velocity (and/or attenuation) images. Tomography data collection involves multiple combinations of source and receiver depth locations. Typically, this is achieved with a vertical string of multiple receivers of between 10-24 hydrophones suspended in water in the borehole while a source is systematically moved up the opposite borehole from bottom to top until all possible source-receiver combinations are recorded. The calculated apparent velocities will equate to actual velocities for each depth, as the energy travels direct from source to receiver.
Common Applications include:
- rock rippability
- image voids, solution caverns, washouts
- locate faults, fractures
- detect water bearing zones
- vertically profile stratigraphic layers
- determine load bearing capacity
- soil elastic moduli (Shear, Young’s, Poisson’s ratio)
- surface seismic survey velocity calibration
- determine depth of piers/pilings
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