Magnetic Anomaly Map of the World


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This map is the first global compilation of the wealth of magnetic anomaly information derived from more than 50 years of aeromagnetic surveys over land areas, research vessel magnetometer traverses at sea, and observations from earth-orbiting satellites, supplemented by anomaly values derived from oceanic crustal ages. The objective is to provide an interpretive dimension to surface observations of the Earth’s composition and geologic structure. Metamorphism, petrology, and redox state all have important effects on the magnetism of crustal materials.

The magnetic anomalies represented on this map originate primarily in igneous and metamorphic rocks, in the Earth’s crust and possibly, uppermost mantle. Magnetic anomalies represent an estimate of the short-wavelenght (< 2600 km) fields associated with these parts of the Earth, after estimates of fields from other sources have been subtracted from the measured field magnitude. In most places the magnetic anomaly field is less than 1 per cent of the total magnetic field.

Studies of crustal magnetism have contributed to geodynamic models of the lithosphere, geologic mapping, and natural resource exploration. Inferences from crustal magnetic fields maps such as these, interpreted in conjunction with other information, can help delineate geologic provinces, located impact structures, dikes, faults, and other geologic entities that have a magnetic contrast with their surroundings. To this end, the Magnetic Anomaly Map of the World is available in both digital and map form. The anomaly field itself is shown at an altitude of 5 km above the WGS84 ellipsoid.

Two digital versions (A and B) of the map, regional grids and updates are available at the WDMAM web site: The B version is shown in the accompanying map. The A version differs in its handling of areas without near-surface data, which are filled in with the downward-continued CHAMP magnetic field model. In contrast, the B version contains both model data derived from CHAMP, and marine ages, with a priority given to the marine age data. Both versions, when upward-continued to satellite altitude, reproduce the magnetic anomaly field derived from the CHAMP satellite.

Release: July 2007
Equatorial scale: 1: 50 000 000
1 sheet : 100 x 73,4 cm
Authors: J.V. Korhonen,J. Derek Fairhead, M. Hamoudi, K. Hemant, V. Lesur, M. Mandea, S. Maus, M.
Purucker, D. Ravat, T. Sazonova & E. Thébault
Printed by the Geological Survey of Finland