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Magnetic anomalies off west coast of North America. Dashed lines are spreading centers on mid-ocean ridges. The Vine–Matthews-Morley hypothesis correlates the symmetric magnetic patterns seen on the seafloor with geomagnetic field reversals. At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma.
The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal). The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface ...
The Bangui magnetic anomaly in central Africa and the Kursk magnetic anomaly in eastern Europe (both in red) 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 ...
The oceanic crust displays a pattern of magnetic lines, parallel to the ocean ridges, frozen in the basalt. A symmetrical pattern of positive and negative magnetic lines emanates from the mid-ocean ridge. [24] New rock is formed by magma at the mid-ocean ridges, and the ocean floor spreads out from this point.
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, [1] the project was coordinated by the International Association of Geomagnetism and Aeronomy, and was presented by Mike Purucker of NASA and Colin Reeves of the Netherlands. [2]
Magnetic surveys discovered linear magnetic anomalies that in many areas ran parallel to an ocean ridge crest and showed a mirror-image symmetrical pattern centered on ridge crests. [21] Correlation of the anomalies to the history of Earth's magnetic field reversals allowed the age of the seafloor to be estimated. [22]
The dense clusters of lines are within the Earth's core. [27] The magnetic field of the Earth, and of other planets that have magnetic fields, is generated by dynamo action in which convection of molten iron in the planetary core generates electric currents which in turn give rise to magnetic fields. [15]
Earth Magnetic Field Declination from 1590 to 1990. The Hydrographic Office, later the Naval Oceanographic Office, was responsible for publishing charts defining components the world magnetic field. After the non-magnetic vessel Carnegie blew up in 1909 collection of oceanic magnetic field information capability was lost. By 1951 those charts ...