Spectral analysis and ridge-regression of magnetic anomalies from the northern continental margin of the Yucatan Peninsula, Mexico

Marine magnetic data from the northern Yucatan continental margin were used to obtain the radially-averaged power-density spectra (RAPDS) of 34 grids, each with dimensions of 128 by 128 km, overlapping 50 percent. Depths to the tops of three magnetic horizons were estimated from the slopes of linear segments in the spectra. The depth to the base of the magnetic crust was estimated using an implicit relationship between the deepest depth estimation and the spectral peak position. The depth determinations agree with the limited drillhole data available and show some consistency with seismic refraction interpretations for the study area. I examined the simplifications implicit in the data processing techniques commonly applied in the spectral analysis of magnetic anomalies. I found that depth interpretations, based upon assuming that the slope of linear segments in the RAPDS are proportional to the average depth to the top of magnetic horizons, and thickness determinations using the position of the spectral peak, are unreliable. I also show that the RAPDS is independent of the direction of both the geomagnetic field and the magnetization vector. It can be represented by a Functional in terms of depth to the top of the source, its thickness and its horizontal dimensions.; The problem of interpreting the RAPDS was then formulated as an inverse problem. A solution was obtained through minimizing, iteratively, the sum of squares of residuals between a real-data spectrum and a synthetic spectrum. The minimization was based on a linearized model, using the ridge-regression algorithm. Depth and thickness determinations, obtained using this technique on the Yucatan spectra, were used to make contour maps of the average depths to the top and the base of the magnetic crust. The top of the magnetic crust is at an average depth of 1.8 km. The base of the magnetic crust is at an average depth of 25 km. Beneath the central Campeche Bank and Campeche Terrace the depth to the base is close to the depth to the crust-mantle boundary determined by gravity modeling and mass column analysis. This suggests that in those regions the mantle is the lower magnetic boundary. (Abstract shortened with permission of author.)...