HR: 14:55h
AN: GP53A-04 INVITED     [Abstracts]
TI: Inversion of magnetic data in three steps
AU: * Mendonca, C
EM: mendonca@iag.usp.br
AF: University of Sao Paulo, Rua do Matao, Sao Paulo, SP 05508090, Brazil
AU: Tuma, S
EM: soraya@iag.usp.br
AF: University of Sao Paulo, Rua do Matao, Sao Paulo, SP 05508090, Brazil
AB: We present a three step magnetic inversion procedure in which invariant quantities with respect to source parameters are sequentially inverted to give i) shape cross-section, ii) magnetization intensity, and iii) magnetization direction for a two-dimensional (elongated) magnetic source. The quantity first inverted (called here the shape function) is obtained from the ratio of the gradient intensity of the total field anomaly to the intensity of the anomalous vector field. For homogenous sources, the shape function is invariant with source magnetization and allows reconstruction of the source geometry by attributing an arbitrary magnetization to trial solutions. Once determined, the source shape is fixed and magnetization intensity is estimated by fitting the total gradient of the total field anomaly (equivalent to the amplitude of the analytic signal of magnetic anomaly). Finally, the source shape and magnetization intensity are fixed and the magnetization direction is determined by fitting the magnetic anomaly. As suggested by numerical modeling and real data application, stepped inversion allows checking if causative sources are homogeneous or not. This is possible because the shape function from inhomogeneous sources can be fitted by homogeneous models but a model obtained in this way neither fits the total gradient of the magnetic anomaly nor the magnetic anomaly itself. Such a criterion seems effective in recognizing strongly inhomogeneous sources. Stepped inversion is tested with numerical experiments, and used to model a magnetic anomaly from intrusive basic rocks from the Parana Basin, Brazil.
DE: 0903 Computational methods: potential fields (1214)
DE: 0910 Data processing
DE: 0920 Gravity methods (1219)
DE: 0925 Magnetic and electrical methods (5109)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly