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The magnetic anomaly of a brick foundation
Author(s) -
Bevan Bruce W.
Publication year - 1994
Publication title -
archaeological prospection
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.785
H-Index - 38
eISSN - 1099-0763
pISSN - 1075-2196
DOI - 10.1002/1099-0763(199412)1:2<93::aid-arp6140010203>3.0.co;2-l
Subject(s) - foundation (evidence) , brick , magnetic anomaly , geology , chapel , magnetic survey , remanence , magnetization , magnetic field , geophysics , seismology , materials science , physics , archaeology , geography , composite material , art history , art , quantum mechanics
This experiment was done at the foundation of a chapel that was constructed about 300 years ago at St Mary's City, Maryland, in the USA. The magnetic anomaly of this foundation is irregular and lumpy. The magnetic map does not show a uniform band with a high magnetic field along the line of the foundation; instead, it shows a series of high readings spaced unevenly near the foundation. This irregularity is caused by the addition and subtraction of the remanent magnetization of randomly oriented bricks in the foundation. Most brick foundations will probably show this irregularity, which will increase where the bricks are larger, the wall is smaller, or the magnetic sensor is closer to the foundation. This irregularity can make it difficult to delineate a buried foundation by magnetic survey. Several bricks were removed from the chapel's foundation and detailed magnetic maps were made of them. An analysis of these maps allowed the remanent and induced magnetization of the bricks to be determined. Having determined typical magnetic parameters for the bricks, simulations of the magnetic maps of brick foundations were constructed. These explain the irregularity of the anomalies.