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Seismic Tomographic Imaging
The principal subsurface information provided by the surface-to-borehole and crosshole seismic tests is in the form of a Seismic Tomographic Image (STI). This is similar to a medical image obtained with Computer Augmented Tomography or CAT scanning.
Seismic tomography is a non-destructive technique for obtaining a 2D image of a slice of the earth by passing sound waves through it. A 3D image may then be built up from a number of scans. In transmission tomography, seismic waves generated at a source point are passed through the earth which modifies these waves according to the nature and variations of elastic properties which are encountered.
These modified waves represent a projection of the internal earth properties and are detected at a number of locations to provide different viewing angles. By combining the information obtained at the different locations an image of elastic property variations is obtained.
The analysis stage involves the numerical simulation of an initial earth model which uses all available information and experience. STI is the highest resolution seismic technique currently available for geotechnical and environmental problems.
STI may be used wherever one or more boreholes or underground openings are available.
Coffey Geotechnics has developed specialised field acquisition, data processing software and interpretation procedures specifically for STI.
Applications:
- detailed assessment of rock mass
- location of shear zones
- location of base of alluvials
- assessment of rock stress
- void delineation
- location of goafed ground
- landfill studies.
Technical Documents
