Exploration of spectral energy from marine and modeled magnetic anomalies

The spectral method has been widely used in various branches of science since it simplifies the analysis of periodic signals. In the case of geophysics, Fourier transform is used to decompose the signal into different wavelengths, and to associate the gradient of the spectral energy to the depth of the source (after Spector and Grant, 1970). This last association is mostly applied in gravity and magnetism, that is, from sources that produce a contrast of density or magnetic susceptibility with respect to the medium. Large part of the mathematical operators used in geophysics rely on the Fourier analysis.

In this work, we set out an analysis of the spectral energy of the magnetic signal in three and two dimensions. We apply this analysis to three cases: the first case, the classical approach, corresponds to the spectral energy calculated from synthetic magnetic anomalies, produced by bodies of simple geometry. In the second case, we use marine magnetic anomalies on a regional scale, specifically of the Caribbean plate, and finally, a third case, where we apply the method on a marine area covering a few square kilometers. Our objective was primarily to explore and characterize the spectral response from another perspective: that of the spectral cube and to estimate depths of magnetic sources from methods previously used to derive only the depth of the Curie isotherm. A first trial in the application of this method was carried out by Garcia-Reyes and Dyment (2020). However, the application of this in other areas allows evaluating its sensitivity to factors such as scale, resolution and quality of the data, the proximity of the source and geometry of the source. This exercise allows us to validate the approach in estimating depths of sources in the subsurface, and in turn, it is a step forward in understanding the spectral cube and the information it provides.

Our results allow us to offer a mapping of the depth of the magnetic sources (detectable in the spectra), and in turn, a three-dimensional view of their spectral energy. These sources are generally correlated with geological structures, as is the case with the results obtained for the Caribbean plate. Beyond the major developments of the spectral method in geophysics, we suggest that the information inscribed in the spectral signature of magnetic anomalies can still be further explored.

 

References:

GARCIA-REYES, Andreina and DYMENT, Jérôme (2020). Spatial Power Spectral Density Distribution of Magnetic Sources in the Gulf of Mexico and Caribbean Plate. In : AGU Fall Meeting Abstracts. p. GP012-0009.

Spector, A., & Grant, F. S. (1970). Statistical models for interpreting aeromagnetic data. Geophysics, 35(2), 293-302.