Power spectra analysis of aeromagnetic data and KTB susceptibility logs, and their implication for fractal behavior of crustal magnetization

Power spectra analysis of aeromagnetic data from the southeast North Sea, where the depth to the top of the magnetic sources is reasonably well constrained, indicates that the scaling factor or spectral exponent (β) in an area with thick sediment cover is likely to be significantly different from the expected value of -3. This is consistent with the results from analyzing the KTB susceptibility data, which show that the magnetic scaling factor changes with burial depth. For sources shallower than about 1 km, a β value of -2.3 is roughly consistent with previous similar investigations. For sources deeper than a few kilometers, the β value could be as low as -1.0. Therefore, the depth estimation using power spectra analysis of magnetic data should be treated with caution, especially if there is no independent constraint on the source depth or the scaling factor (for instance from susceptibility logs in boreholes).