The World Digital Magnetic Anomaly Map (WDMAM) was first made available by the Commission for the Geological Map of the World in 2007. Compiled with data from governments and institutes, the project was coordinated by the

International Association of Geomagnetism and Aeronomy The International Association of Geomagnetism and Aeronomy (IAGA) is an international scientific association that focuses on the study of terrestrial and planetary magnetism and space physics. IAGA is one of the eight associations of the Interna ...

, and was presented by Mike Purucker of

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

and Colin Reeves of the Netherlands. As of 2007, it was considered to be "the first truly global compilation of lithospheric magnetic field observations." and further improvements dated to 2009 relate to the full spectrum

magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

grid of the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

and also data of global marine magnetic anomaly. Some of the magnetic anomalies shown in the WDMAM generally relates to the altitude level of . Some of the significant features represented are of the

Bangui Anomaly The Bangui magnetic anomaly is a local variation in the Earth's magnetic field centered at Bangui, the capital of Central African Republic. The magnetic anomaly is roughly ellipse, elliptical, about , and covers most of the country, making it one ...

in the

Central African Republic The Central African Republic (CAR; ; , RCA; , or , ) is a landlocked country in Central Africa. It is bordered by Chad to the north, Sudan to the northeast, South Sudan to the southeast, the DR Congo to the south, the Republic of th ...

, the

Chicxulub crater The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large ast ...

, the Thromsberg anomaly, the

Richat Structure The Richat Structure, also called ''Guelb er Richât'' ( ar, قلب الريشات, Qalb ar-Rīšāt), is a prominent circular geological feature in the Sahara's Adrar Plateau, near Ouadane, west–central Mauritania, Northwest Africa. In t ...

, the Atlantic ridge, the

Bay of Biscay The Bay of Biscay (), known in Spain as the Gulf of Biscay ( es, Golfo de Vizcaya, eu, Bizkaiko Golkoa), and in France and some border regions as the Gulf of Gascony (french: Golfe de Gascogne, oc, Golf de Gasconha, br, Pleg-mor Gwaskogn), ...

, the

Sunda Arc The Sunda Arc is a volcanic arc that produced the volcanoes that form the topographic spine of the islands of Sumatra, Nusa Tenggara, and Java, the Sunda Strait and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, ...

and the

Paris Basin The Paris Basin is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in the cr ...

Background

WDMAM v1, 2007

In evolving the WDMAM the lithospheric data related to data acquired from satellites, data of aero-magnetic survey and marine survey, in-situ data gathered from field stations and observatories are to be collated analyzed together, and this would need an international joint effort. The map is the product of years of work, research and coordination by the

(IAGA) and numerous small organizations around the world including GETECH, a project of

Leeds University , mottoeng = And knowledge will be increased , established = 1831 – Leeds School of Medicine1874 – Yorkshire College of Science1884 - Yorkshire College1887 – affiliated to the federal Victoria University1904 – University of Leeds , ...

, and Juha Korhonen of the

Geological Survey of Finland The Geological Survey of Finland ( fi, Geologian tutkimuskeskus abbreviated GTK, sv, Geologiska forskningscentralen) is the geological survey of Finland. The organization was founded in 1885 when Emperor Alexander III decreed that the Geological ...

have also been involved. International collaboration has been the key to the project. Mike Purucker of NASA said of the collaboration: "There are literally hundreds, perhaps thousands, of organisations around the world which hold this kind of data. One should not underestimate the diplomatic efforts needed to secure support and data contributions from these organizations." Diplomacy was needed to acquire data from the Russians, Indians, and Argentinians and so on. It is available through the Commission for the Geological Map of the World. The map is compiled from a jigsaw of aeromagnetic surveys, incorporating both ground-based, airborne and marine magnetic data, but is incomplete. CHAMP, a German and Russian-built satellite which has been in orbit since 2001, has been of crucial importance to the map compilers. One of its principal achievements is that it has significantly improved the "pre-processing and the corrections applied to the CHAMP satellite measurements in order to obtain 'clean' satellite data compatible with ground data." However, it has some large gaps in data, which is a hindrance to studying trans-national tectonics, and could benefit from further satellite observational additions to improve its coverage. Several different models were put forward as candidates for WDMAM by groups from NASA, Leeds University, the Geological Survey of Finland,

National Geophysical Data Center The United States National Geophysical Data Center (NGDC) provided scientific stewardship, products and services for geophysical data describing the solid earth, marine, and solar-terrestrial environment, as well as earth observations from spac ...

(NGDC) and GeoForschungszentrum Potsdam, all using the same base data. Following a review, the NGDC candidate was chosen to form the basemap. Specified to a grid of three arcminutes, the WDMAM v1 was based on the NGDC's EMAG3 (Earth Magnetic Anomaly Grid, 3 arcminute) dataset. The EMAG has since been improved into EMAG2 at a resolution of two arcminutes and fitted into the

Enhanced Magnetic Model The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey. The data and updates are issued by the U ...

WDMAM v2, 2015

Composition

According to the BBC, the "global map shows the variation in strength of the magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000

nano- Nano (symbol n) is a unit prefix meaning "one billionth". Used primarily with the metric system, this prefix denotes a factor of 10−9 or . It is frequently encountered in science and electronics for prefixing Unit of measurement, units of tim ...

Tesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks." The map is graphically represented by illustrating those landmarks of high magnetism in red to yellow hues and those of lower or negative magnetism in blue hues. It can pick up numerous aspects of the earth composition, including the sea floor spreading under the oceans, and reserve deposits like iron ore at

Kursk Kursk ( rus, Курск, p=ˈkursk) is a city and the administrative center of Kursk Oblast, Russia, located at the confluence of the Kur, Tuskar, and Seym rivers. The area around Kursk was the site of a turning point in the Soviet–German stru ...

. It identifies some prominent magnetic anomalies on the African continent. The dominant factors for magnetic anomalies picked up on the map are "the thickness of the magnetised layer and the composition of the crust". Younger crust is typically thinner, and naturally has a lower number of magnetic materials.

References

Bibliography

External references

* {{official website, http://wdmam.org
WDMAM download page
21st-century maps and globes Magnetic anomalies Projects established in 2007