Refraction Seismic

Seismic waves are parcels of elastic strain energy that propagate outwards from a seismic source, e.g. an explosion. By virtue of geological materials various compositions, textures, porosities and contained pore fluids, rocks and soils differ in their elastic moduli and densities and hence, in their seismic velocities. Seismic refraction surveys are based on the times of arrival of the initial ground movement generated by a source recorded at a variety of distances. Thus, the data set derived from refraction measurements consists of a series of times versus distances. These are then interpreted in terms of the depths to subsurface interfaces and the velocities at which motion travels through the subsurface within each layer. Seismic refraction surveys can be successfully applied to explore geological structures exhibiting a low number of interfaces where the seismic velocity increases with depth. Refraction seismic can therefore be used to map the soil cover thickness, groundwater table and the quality of the bedrock beneath in terms of fractured rock. This method is commonly used when planning for larger constructions, e.g. roads, railways, tunnels or larger buildings.

Reference projects

– Investigations for new roads and railway in Kiruna
– Investigation of deformation zones in Stenungsund

The image show a seismic refraction tomography section with clear distinction of soil cover, bed rock and fracture zones.