Magnetic Anomaly Map of the World


Equatorial scale: 1:50 000 000
Published in July 2007
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

Availability: In stock

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This map is the first global compilation of the vast amount of data collected over the past 50 years from aeromagnetic surveys of land areas, magnetometry profiles recorded during sea campaigns to assess the age of the oceanic crust, and satellite observations.

The objective of this map is to contribute to the interpretation of surface observations of the composition and geological structure of the Earth. Metamorphism, petrology, and redox states have important effects on the magnetic state of the minerals that constitute the crustal material. The magnetic anomalies shown on this map originate from the formation and composition of the igneous and metamorphic rocks of the Earth's crust, probably from the upper part of the Earth's mantle, i.e. from a set corresponding to the lithosphere.

The so-called magnetic anomaly field is roughly the lithospheric field that represents the difference between the measured data, which includes all magnetic sources, and the estimated core and external field. This anomalous field is therefore created within the magnetic lithosphere, but it is important to bear in mind that only structures with an amplitude of less than 2500 km can be taken into account. In almost all cases, the magnetic anomaly field represents less than 1% of the total magnetic field.

The study of crustal magnetism has contributed to the development of geodynamic models of the lithosphere, geological mapping and natural resource exploration. Data from Earth magnetism maps such as the one presented here, in conjunction with other information, can be very useful in defining geological provinces, locating impact structures, dykes, faults and other geological formations with magnetic contrasts to their surroundings. For this reason, the Magnetic Anomaly Map of the World is published in print and digital form, together with a database on DVD. The magnetic field shown on the map corresponds to an altitude of 5 km above the WGS84 ellipsoid.

Two versions of the map (A and B), plus regional data and other databases and updates are available on the WDMAM project website: It is version B that is shown in the printed map. In version A the near-surface data were not taken into account and were replaced by the downwardly extended CHAMP magnetic field model. In contrast, version B contains both data models derived from the CHAMP and the sea ages with priority given to the latter. Both versions, when extended upwards to satellite altitude, reproduce the magnetic anomaly field derived from the "satellite CHAMP".

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