Deep seismic surveying

Earthquakes, and other sources, produce different types of seismic waves. These waves travel through the bedrock, and provide an effective way to image both sources and structures deep within the Earth.

Seismic waves

There are three basic types of seismic waves in solids: P-wave and S-wave (both body waves) and surface waves. The two basic kinds of surface waves (Rayleigh and Love), can be fundamentally explained in terms of interacting P- and/or S-waves.

Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometres. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.

Earthquakes

The passive seismic method can also be used to image the deep crust and upper mantle recording teleseismic arrivals along semi-permanent networks (e.g. SCANLIPS). A network of seismographs, instruments that sense and record the travel time of seismic waves through the Earth, are positioned along a profile or outline an area to record the response of earthquakes at great distances (almost the other side of the world) by measuring their travel time through the Earth.

Differences in travel-times from different directions allow us to image regional structures.

Seismometer with geophoneSeismic waves produced by explosions or controlled vibrating-sources are the primary method of underground exploration.

Labour-extensive

Controlled-source seismology, often called active seismics, has been used to map faults, anticlines and in general the structure of the crust below southern Norway.

This type of seismic registration is often very labour-extensive, and dozens of people can be involved in the data acquisition, as a large number of seismographs is usually deployed (see picture).