HR: 15:30h
AN: GP24A-01 INVITED     [Abstracts]
TI: Recent Advances in Quantitative Interpretation of Magnetic Data in the Presence of Strong Remanent Magnetization
AU: * Li, Y
EM: ygli@mines.edu
AF: Center for Gravity, Electrical, and Magnetic Studies, Department of Geophysics, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401 United States
AU: Shearer, S
EM: sshearer@mines.edu
AF: Center for Gravity, Electrical, and Magnetic Studies, Department of Geophysics, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401 United States
AU: Haney, M
EM: mhaney@mines.edu
AF: Center for Wave Phenomena Department of Geophysics, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401 United States
AU: Dannemiller, N
EM: ndannemi@mines.edu
AF: Center for Gravity, Electrical, and Magnetic Studies, Department of Geophysics, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401 United States
AB: Three-dimensional (3D) inversion of magnetic data to recover a distribution of magnetic susceptibility has been successfully used for mineral exploration for the last decade. However, such inversion algorithms depend critically upon a known magnetization direction, which is commonly assumed to be the same as the direction of the ambient field. This central assumption has severely limited the application of these methods to allied disciplines where the presence of remanent magnetization is a rule rather than exception. The difficulty arises because the total magnetization, which is a vector sum of the induced and remanent magnetization, can be rotated away from the inducing field direction if the remanent magnetization is strong and not aligned with the inducing field. To overcome this difficulty, we develop two parallel attacks. In the first, we estimate the direction of total magnetization and supply it to the inversion algorithm, assuming that the magnetization direction does not vary greatly within the target region. We have developed two methods for estimating magnetization direction. Alternatively, we accept the fact that a single direction may not be estimated for various reasons and proceed to directly invert quantities that are derived from magnetic data but are weakly dependent upon the magnetization direction. We have developed an algorithm that constructs 3D distributions of the magnitude of magnetization by inverting either the amplitude of anomalous magnetic field or the total gradient of a component. This algorithm does not require explicit knowledge of magnetization direction. In this paper, we present the details of both approaches and examine their effectiveness using synthetic and field examples. It is now possible to invert virtually any magnetic data arising from geophysical problems by using these two complementary approaches. They open the door to 3D quantitative interpretation of magnetic data in a variety of applications including archaeology, environmental problems, crustal study, and planetary exploration.
DE: 0903 Computational methods, potential fields
DE: 0925 Magnetic and electrical methods
DE: 1517 Magnetic anomaly modeling
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly