Deep-pass — An aeromagnetic data filter to enhance deep features in marginal basins

Abstract

An aeromagnetic data filter was tested as a tool in enhancing the magnetic responses of deep sources associated with marginal basins. Our approach consists in amplifying the responses of magnetic sources which extend through the continental slope and continental rise. This amplification compensates for the magnetic response attenuation over the continental slope as a result of (1) the seaward increase of the distance between the source and the magnetometer and (2) the seaward decrease in the volume of sources within the continental crust. To amplify the source response, we multiply the total-field anomaly at a given location by the exponential of the bathymetric depth at the same point. Tests on synthetic and real data showed that the filter was able to recover the locations of linear magnetic responses not clearly seen in the total-field-anomaly map. When compared with the analytic signal amplitude and the total horizontal derivative filters, the proposed filter proved to be complementary in enhancing lineaments with different orientations. When applied in conjunction with these filters, the proposed filter produced a synergistic effect, revealing lineaments that were not present in individual applications of the filters. The application of the filter to an offshore Brazilian margin comprising the Camamu-Almada and Jequitinhonha marginal basins highlighted northwest–southeast and northeast–southwest lineaments not clearly seen in the total-field data. The northeast–southwest lineaments were interpreted as related to fracture zones that may cut across the continental margin, controlling basement structures and fluid migration paths.