Magnetic field

Small variations in the strength of the geomagnetic field can be registered with airborne geophysical measurements. This can be used to obtain information on, for example, depth and surface distribution of different rock types, as well as their strike and dip. Faults and their relative movement can in some cases also be identified in the magnetic patterns.

Soils or water does not affect a magnetic field measurement, which make it an important method for mapping bedrock where it cannot be directly observed.

The map shows measured variations in the magnetic total field after subtraction of the geomagnetic reference field (DGRF 1965.0). The map is based on measurements carried out 1960–2020.

The magnetic properties of the Earth's crust are mainly determined by the content of the mineral magnetite in various rock types. The concentration may vary from nearly zero up to 10% or more in gabbros, and up to almost 100% in iron ores.

The magnetic field has been measured and registered in systematic and detailed airborne surveys. Measured data are corrected and stored in digital form in databases and may for instance be visualized as maps.

The distribution of various rock types at surface and depth is reflected by the anomaly pattern in the map. The extension of rock types, strike and dip direction can be determined using geophysical interpretation techniques. Faults and their relative movements can be seen as dislocations in the magnetic pattern.

Last reviewed 2021-03-18