Háskóli Íslands

Crustal processes

A good part of the research effort of the Institute of Earth Sciences is directed toward the Earth´s crust, its composition, generation, movements, and fracturing.  Iceland is particularly well suited for research in this field, being one of few places on Earth where these processes can be observed above sea level. New crust is generally formed at divergent plate boundaries and most of them are on mid-oceanic ridges beneath 2-3 thousand meters of water.

Several research methods are applied at the institute. Petrological analyses give information on the chemical composition of the crust and the chemical processes at work. The structure of the crust is investigated by seismic refraction methods. Seismic waves from man-made earthquakes are measured and their path traced through the crust. Surface waves from earthquakes around Iceland are also used to investigate the structure of the crust and the uppermost layers of the underlying mantle. Body waves (P- and S-waves) from distant earthquakes can be used to make tomographic images of the mantle beneath Iceland. They show the location of a plume of hot but solid material, slowly rising beneath Iceland. It partially melts and feeds the abundant volcanism of Iceland. Measurements of seismic wave attenuation give information on the physical properties of the material they pass through. Partially molten material attenuates the waves more than solid material. Molten material does not transmit S-waves at all.

Repeated, precise geodetic surveys are used to determine movements of the Earth´s crust. GPS-geodesy conducted on a countrywide scale shows the movements of the two major lithospheric plates, North America and Eurasia, as they move apart. The measurements also show how the interior of Iceland is rising in response to the un-loading of the

crust, as the glaciers are melting due to global warming. Crustal deformation around volcanic centers gives indications about magma movements in their roots. Harnessing of geothermal heat also leads to measureable deformation of the crust around geothermal power plants. GPS-geodetic measurements are conducted both in a campaign-mode, i.e. temporary measurements on dense networks of points, and in a continuous mode, where an instrument is installed permanently and operated for a long time in the same place. InSAR-measurements, interferometric radar measurements from satellites, give a 2-dimensional map of the deformation field over a large area. Gravity measurements give information about mass movements, e.g. movements of magma in the roots of volcanoes.

The Earth´s crust breaks when it is exposed to high stress. The sudden movement generates waves that propagate from the point of failure. This constitutes an earthquake. By measuring the waves on a network of seismographs the source can be located and the focal mechanism of the event can be determined, i.e. the movement along the fault plane that produced the event. Measurements of the crustal movement around the fault by GPS and InSAR can also be used to deduce the movements along the fault plane. Fault movements often extend to the surface of the Earth and leave a pattern of fractures. Fracture mapping can give valuable information on the fault movements at depth, e.g. whether strike-slip took place like in the South Iceland Seismic Zone, or whether divergent motion dominates, s.a. in the fissure swarms of the volcanic zones, e.g. along the plate boundary in North Iceland.

Measurements of crustal movements indicate where stress is building up and how fast. They therefore have some predictive value as to the location and timing of the next large earthquakes. Radon measurements in hot groundwater have also been conducted for the same purpose. Several cases are known where radon changed shortly before earthquakes. Significant changes in radon were detected in conjunction with the earthquakes in South Iceland in 2000.

Model calculations are frequently used for comparison with measured data for the purpose of interpretation. Comparisons may also be useful with other areas in the world where similar processes are at work.

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