Seismic crosshole tomography

The basic principle of seismic crosshole tomography is to estimate a velocity model of the subsurface by measuring the time it takes for elastic waves to propagate from a source to a receiver. The elastic wave velocity is related to mechanical properties such as Shear Modules, Compression Module and Shear Strength. It is necessary to have two (or more) boreholes. An array of geophones is inserted in one hole and in the other an elastic wave is generated. A seismograph measures the time it takes for the wave to propagate from the source point to the geophones. The source is then moved to another position in the hole and the procedure is repeated. The measurements will produce a number of arrival times from waves that have crossed the investigated area. The geophone distance and the wave frequency mainly govern the data resolution, the shorter distance and higher frequency the better resolution. The geometry of the investigated area and distance to the boreholes are also important parameters since shallow boreholes and a large distance will lead to unfavourable ray coverage. This method is mainly designed for geotechnical applications such as characterization of soils according to their mechanical properties or preparation of larger constructions.

Reference projects

– Reinforcement of embankment in Norrköping
– Hydro power embankment dams in Norrbotten
– Basic investigations – Stenungsund and Sundsvall