We present a 3‐D interpretation of the deep magnetic sources beneath the main geological structure of central‐eastern Europe, the “Trans‐European Suture Zone” (TESZ). We used a multiscale analysis of aeromagnetic data, based on a multiscale data set generated by upward continuation of the European and Mediterranean Magnetic Project data set from 5 to 100 km altitude. We also computed the multiscale total gradient |∇T| of the multiscale field. Both of the multiscale data sets allow us to discriminate the main crustal contributions to the field at various scales, and we showed that at large altitudes the field is dominated by the sole effect of the TESZ. The multiridge geometric method was very useful in studying the complex features of the main crustal interfaces, either shallow or deep. The interpreted interfaces are largely agreement with geological models based on seismic surveys and, in some cases, complete the models out of the analyzed region. In order to estimate the deepest source depths in the TESZ region, we applied the multiridge method to the large scales (50–100 km altitude), obtaining a set of singular points at depths ranging between 35 and 40 km. Considering the heat flow trend and the geological models around the TESZ area, we found a meaningful correspondence among the location of the estimated singular points and the most abrupt variations and complex morphology features of the Moho boundary. The multiridge estimates are consistent with known structural information and can be used for a 3‐D representation of the Moho depth along the TESZ.
We show that high-resolution aeromagnetic surveys, although rarely employed in the research of salt structures, may be an effective and low-cost tool for mapping diapirism. A multiscale analysis of a high-resolution magnetic data set at Nordkapp Basin in the Barents Sea, allows a clear reconstruction of the main salt diapirs of the basin using Multiridge and Compact Depth from Extreme Points methods. We provide a 3-D model of the diapirs extended from 500 to 4,000 m below sea level, characterized by a general low magnetization contrast no larger than −0.08 A/m. The 3-D model is consistent with the salt top depth estimated by 2-D seismics, with borehole data and with the 2-D gravity model of the Uranus diapir. Our imaging shows the capability of the magnetic method that gives new and comprehensive pictures of salt diapirism.
Spectral analysis has been used for studying a variety of geological structures and processes, such as estimation of the depth to the crystalline basement or of the Curie temperature isotherm from magnetic anomalies. However, the analysis is not standard, as it refers to different theoretical frameworks, such as statistical ensembles of homogeneous sources and uncorrelated or fractal random distributed sources. In this review, we aim to unify the approaches by reformulating all the common spectral expressions in the form of a product between a depth-dependent exponential factor and a factor, which we call the spectral correction factor, that incorporates all of the a priori assumptions for each method. This kind of organization might be useful for practitioners to quickly select the most appropriate method for a given study area. We also establish a new formula for extending the Spector and Grant method to the centroid depth estimation. Practical constraints on the depth estimation and intrinsic assumptions/limitations of the different approaches are examined by generating synthetic data of homogenous ensemble sources, random and fractal models. We address the statistical uncertainty of depth estimates using ordinary error propagation on the spectral slope. Critical parameters, such as the window size, are also analyzed in terms of the type of method used and of the geological complexity. We find that the window size is smaller for the centroid/modified centroid methods and larger for the spectral peak, de-fractal, and nonlinear parameter depth estimation methods. In any case, the window size can be large in tectonically stable regions and relatively small over volcanically, tectonically, and geothermally active areas. We finally estimate and discuss the depth to magnetic top and bottom in the Adriatic Sea region (eastern Italy) in the context of heat flow, Moho depth, and gravity data of the region.
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