magnetic anomaly

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magnetic anomaly

geophysics

Also known as: geomagnetic anomaly

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July 23, 2026

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A magnetic anomaly is a deviation from the expected magnetic field strength at a specific location. In geophysics, these anomalies are studied to understand the Earth's subsurface structure and composition. They arise from variations in the magnetic properties of rocks within the Earth's crust.12

These variations can be due to induced magnetism, where crustal materials align with the Earth's main magnetic field, or remnant magnetism, which is a permanent magnetization acquired by rocks as they form and cool. Magnetic surveys, often conducted from aircraft or ships using magnetometers, map these anomalies. By analyzing the patterns of magnetic anomalies, geophysicists can infer the presence of mineral deposits or geological structures beneath the surface. For instance, in petroleum exploration, magnetic anomalies can indicate the absence of sedimentary rocks suitable for oil accumulation.231

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paleogeography
Linear magnetic anomalies
Earth’s magnetic field has another important property. Like the Sun’s magnetic field, Earth’s magnetic field periodically “flips,” or reverses polarity—that is, the North and South poles switch places. Fluctuations, or anomalies in the intensity of the magnetic field, occur at the boundaries between…
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Earth’s magnetic field has another important property. Like the Sun’s magnetic field, Earth’s magnetic field periodically “flips,” or reverses polarity—that is, the North and South poles switch places. Fluctuations, or anomalies in the intensity of the magnetic field, occur at the boundaries between…
Read More

plate tectonics
Magnetic anomalies
In 1961 a magnetic survey of the eastern Pacific Ocean floor off the coast of Oregon and California was published by two geophysicists, Arthur D. Raff and Ronald G. Mason. Unlike on the continents, where regional magnetic anomaly patterns (that is, magnetic patterns…
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In 1961 a magnetic survey of the eastern Pacific Ocean floor off the coast of Oregon and California was published by two geophysicists, Arthur D. Raff and Ronald G. Mason. Unlike on the continents, where regional magnetic anomaly patterns (that is, magnetic patterns…
Read More

seafloor spreading
Investigations of oceanic magnetic anomalies have further corroborated the seafloor spreading hypothesis. Such studies have shown that the strength of the geomagnetic field is alternately anomalously high and low with increasing distance away from the axis of the mid-ocean ridge system. The anomalous features are nearly symmetrically arranged…
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Investigations of oceanic magnetic anomalies have further corroborated the seafloor spreading hypothesis. Such studies have shown that the strength of the geomagnetic field is alternately anomalously high and low with increasing distance away from the axis of the mid-ocean ridge system. The anomalous features are nearly symmetrically arranged…
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oceanic crust
Study of ophiolites
A marine magnetic anomaly is a variation in strength of Earth’s magnetic field caused by magnetism in rocks of the ocean floor. Marine magnetic anomalies typically represent 1 percent of the total geomagnetic field strength. They can be stronger (“positive”) or weaker (“negative”) than the average total…
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A marine magnetic anomaly is a variation in strength of Earth’s magnetic field caused by magnetism in rocks of the ocean floor. Marine magnetic anomalies typically represent 1 percent of the total geomagnetic field strength. They can be stronger (“positive”) or weaker (“negative”) than the average total…
Read More