Borehole Tomography

• Bedrock mapping
• Location of fault/fracture zones
• Void detection
• Subsurface profiling
• Imaging velocity inversions (hard layer overlying softer layer)
• Deep profiling with limited space
• High accuracy geotechnical parameters at depth

The borehole tomography method utilises existing or new boreholes to allow for seismic source and/or receivers to be placed at depth improving resolution which is typically lost from surface-only methods. Borehole tomography measures the direct arrival times from the source to the receiver to produce a 2D slice of P- or S-wave velocities which can be used to determine the subsurface structure. A number of configurations can be used depending on available boreholes and required outcomes. Common configurations include surface to borehole and crosshole (borehole to borehole). A modified borehole tomographic technique using a receiver array placed in a sewer can produce valuable information regarding the variations in compaction between the road surface and top of the sewer.

Direct travel times between source and receiver arrays calculate and processed to generate a 2D slice showing variations in either P- or S-wave velocity depending on the source type. Each dataset is processed using multiple inversions to reduce RMS error. By using multiple source/receiver locations over several boreholes or a sweep of surface sources recording from a single borehole a pseudo-3D model can be generated.