An anomalous magnetic field refers to deviations in Earth’s magnetic field from the expected normal pattern. These anomalies can be caused by variations in the Earth’s crust, such as the presence of different types of rocks, or by external factors like solar wind. Studying these anomalies helps geophysicists understand the structure of the Earth’s crust and mantle, as well as past movements of tectonic plates.
Source Dyment, J., & Arkani-Hamed, J. (1998). “Geophysical Interpretation of Anomalous Magnetic Fields.” Geophysical Journal International, 133(2), 435-456.