THE SEPARATION OF REMANENT FROM INDUCED MAGNETISM OF NEAR-SURFACE ROCKS BY MEANS OF IN SITU MEASUREMENTS,

A distinction between induced and remanent magnetism of near-surface rocks can be obtained by means of a careful analysis of geomagnetic fluctuations. Diagnostic information concerning the type of magnetization possessed by nearsurface rocks is revealed from a study of the magnetic time variations for the following reasons 1 the intensity of remanent magnetization is independent of the strength of an external field, 2 the intensity of induced magnetization, on the other hand, is directly proportional to the strength of an external field except for demagnetization effects, and 3 at the low frequencies of the geomagnetic oscillations secondary magnetic fields due to an eddy current response in earth materials do not arise. A measure of the intensity of induced magnetization can be obtained from the amplitude of time variations observed simultaneously at two or more sites in the vicinity of a static field anomaly. The spatial variation of induced alternating magnetic fields can then be used to estimate magnetic susceptibility of the buried rocks. Author