LAND
GEO has a range of commercial and in-house designed equipment specialized to equip a range of geological field studies. These include, for example, speleology, soft sediment core drilling, geological mapping, subsurface profiling, seismic, section logging and sampling for exposure dating. Terrestrial fieldwork at GEO is mainly associated with the Quaternary Earth Systems and Basin and Reservoir Studies research groups.
About
Land seismics
Land seismic surveys are conducted to map the structure and stratification of the Earth's crust on a small and large scale. This is central to understanding which processes have been decisive for today's geological picture. Land seismic surveys are important in prospecting for hydrocarbons and mineral deposits, but will also become an important component in monitoring greenhouse gases that will be deposited in rocks below the surface on land. Furthermore, land seismic data provide valuable information when planning tunnels and mapping weak zones in rocks and sedimentary structures. In the 1970s, large land seismic surveys were conducted under the auspices of the University of Bergen with the aim of finding the transition between the Earth's lower crust and the mantle (Moho) in the western part of Scandinavia.
Methods and instrumentation
Collection of land seismic data will be carried out according to the same principles as in marine seismic surveys. However, land seismic surveys are generally more difficult and extensive to conduct due to complex topography, vegetation, local geological conditions and, not least, buildings and other infrastructure. The surveys are carried out by placing geophones in a network on the surface in the area to be surveyed. The geophones measure local vibrations on the surface in all directions. These vibrations are initiated either by a source that can be one (or more) explosions on the surface or by using vibrators, heavy machines that stand and vibrate on the surface for several seconds. The vibrations generated by the source propagate downwards in the soil as pressure and shear waves, which in turn are reflected in the transitions between rocks of different densities and/or stiffness. By seismic processing we are able to find the different speeds at which these waves propagate in each layer, and the times they take from the source down to the various rock boundaries. This information is systematized so that we can finally create a two- or three-dimensional picture of the different rock boundaries and sometimes also what the different rock types consist of.
The institute has various systems for collecting seismic data on land and in the transition from land to sea. In the late 1980s, the institute was involved in the development of the snow streamer, a cable with geophones that is towed behind a tracked vehicle. This method, which is very similar to marine seismic, achieves high efficiency, but can only be used in flat and snow-covered areas with little vegetation. The source is a detonating fuse that is fired on the surface. In recent years, the institute has invested in node-based collection systems. These are small, battery-powered computers that record and store data from connected sensors (geophones or hydrophones). The advantage of such systems compared to traditional land seismic is that long cables from the geophones to a central recording unit are not needed. The institute has 120 nodes for land seismic and several hundred nodes (Trilobite) that can be placed on the seabed, e.g. in the transition zone between sea and land.