Satellite measurements of the Earth's crustal magnetic field

Abstract

The capabilities and limitations of satellite measurement of the Earth's crustal magnetic field have been described and quantified in over 125 scientific papers produced from the Magsat mission. This body of work demonstrates there is a long-wavelength (300 to 3000 km) magnetic field related to major features in the Earth's crust. Thus high sensitivity magnetic measurements by satellite provide a new, heretofore unavailable, view of the deep crust. This field is chiefly caused by induction, although there are areas, such as oceanic quiet zones, where variations in the crustal field are caused by large-scale variations in remanent magnetization. On a continental scale, the influence of variations in crustal thickness and magnetic susceptibility are about equal in producing magnetic anomalies. Due to its scale and sensitivity, satellite data have been particularly useful to develop and define models of large crustal features such as subduction zones, submarine platforms, continental accretion boundaries, and rifts. Some unanswered questions from the Magsat study involve the lack of a magnetic expression of some first-order crustal features, the lack of agreement between laboratory and satellite estimates of lower crustal magnetization, and the origin of long anomalies which cross oceanic-continental boundaries, the most notable being trans-South Atlantic anomalies which cross continental boundaries in both South America and Africa. Computer simulations indicate the great potential of future, lower altitude missions.