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Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the central Rio Grande rift, New Mexico

¹ U.S. Geological Survey, MS 964, Federal Center, Denver, Colorado 80225-0046, USA
² U.S. Geological Survey, MS 980, Federal Center, Denver, Colorado 80225-0046, USA

High-resolution aeromagnetic data acquired over several basins in the central Rio Grande rift, north-central New Mexico, prominently display low-amplitude (5–15 nT) linear anomalies associated with faults that offset basin-fill sediments. The linear anomalies give an unparalleled view of concealed faults within the basins that has significant implications for future basin studies. These implications provide the impetus for understanding the aeromagnetic expression of faults in greater detail. Lessons learned from the central Rio Grande rift help to understand the utility of aeromagnetic data for examining concealed faults in sedimentary basins in general. For example, linear anomalies in the rift can be explained entirely by the tectonic juxtaposition of magnetically differing strata rather than the product of chemical processes acting at the fault zone. Differences in layer thickness, depth to the layer(s), and magnetic susceptibility govern the variability of the anomaly shape. Further investigations of these variables using simple models provide graphical, mathematical, and conceptual guides for understanding the aeromagnetic expression of faults, including the criteria for aeromagnetic expression of faults, how to locate fault traces from aeromagnetic anomalies, the effect of fault dip, and how to assess the role of topography. The horizontal gradient method applied to reduced-to-pole aeromagnetic data is particularly effective in mapping fault locations, especially at regional scales. With our new understanding of the aeromagnetic expression of faults, we updated interpretations of faults from the aeromagnetic data for the central Rio Grande rift. These interpretations, along with the guides, should provide direction and fuel for future work in a wide variety of multidisciplinary basin-related topics.

Keywords: aeromagnetic surveys • faults • faulting • sedimentary basins • rifts