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Calculating depths to shallow magnetic sources using aeromagnetic data from the Tucson Basin

Open-File Report 2001-505
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https://doi.org/10.3133/ofr01505

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Abstract

Using gridded high-resolution aeromagnetic data, the performance of several automated 3-D depth-to-source methods was evaluated over shallow control sources based on how close their depth estimates came to the actual depths to the tops of the sources. For all three control sources, only the simple analytic signal method, the local wavenumber method applied to the vertical integral of the magnetic field, and the horizontal gradient method applied to the pseudo-gravity field provided median depth estimates that were close (-11% to +14% error) to the actual depths. Careful attention to data processing was required in order to calculate a sufficient number of depth estimates and to reduce the occurrence of false depth estimates. For example, to eliminate sampling bias, high-frequency noise and interference from deeper sources, it was necessary to filter the data before calculating derivative grids and subsequent depth estimates. To obtain smooth spatial derivative grids using finite differences, the data had to be gridded at intervals less than one percent of the anomaly wavelength. Before finding peak values in the derived signal grids, it was necessary to remove calculation noise by applying a low-pass filter in the grid-line directions and to re-grid at an interval that enabled the search window to encompass only the peaks of interest. Using the methods that worked best over the control sources, depth estimates over geologic sites of interest suggested the possible occurrence of volcanics nearly 170 meters beneath a city landfill. Also, a throw of around 2 kilometers was determined for a detachment fault that has a displacement of roughly 6 kilometers.

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Calculating depths to shallow magnetic sources using aeromagnetic data from the Tucson Basin
Series title Open-File Report
Series number 2001-505
DOI 10.3133/ofr01505
Year Published 2001
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 231 p.
Country United States
State Arizona
Other Geospatial Tucson Basin
Google Analytic Metrics Metrics page
Additional publication details