::. Seismic Refraction Surveys .::

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Subsurface Imaging

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Seismic Refraction Surveys

SSI Capability

Surface Surveys
Crosshole Surveys
Crosshole Shearwave surveys

The seismic refraction method measures the travel time of seismic waves travelling along subsurface layers. A Shot or source, at surface or downhole provides the energy. Energy radiates out from the shot point, either travelling directly This energy is detected on surface using a linear array of geophones or downhole using an array of phone or a single multi-component phone. Processing this data gives the seismic velocities.

$Seismic refraction schematic$
Surface Seismic Refraction Survey

USE of P and S wave surveys for FOUNDATION DESIGN

The building codes give an opportunity to use shear wave velocities to determine foundation types.

This is an example of using the method

Crosshole Shear wave survey Surface to downhole surveys

A Schematic of a typical Crosshole survey setup, either bore to bore or surface to downhole

Running cross-hole shear wave surveys

graph of shear wave velocity

This is an example of cross-hole data, the depth below surface is on the horizontal axis, the velocity is on the vertical axis

The processed data is normally shown in three plots; time-distance graphs for the first-arrivals on each shot, a true depth profile for the refractors and a velocity profile for the overburden and refractors. Any existing ground truth information such as borehole and trial pit logs, is overlain on the depth profile. This helps calibrate the seismic results and then provide an idea of what the velocity structure means in terms of the geology.

Another way to get information is to use a slowness image or tomographic Image. SSI also have the capability to do this with Resistivity, Bore Radar or Radio Tomography.

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