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

Abstract

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-fi ll sediments. The linear anomalies give an unparalleled view of concealed faults within the basins that has signifi cant 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.

Geophysical evidence of pre-sag rifting and post-rifting fault reactivation in the Parnaíba basin, Brazil

“…They proposed two rift stages before sag sedimentation, but that model needed confirmation by more specific geophysical and/or geological information. Airborne geophysical data are used worldwide to map large-scale crustal structures (e.g., Nabighian et al, 2005;Grauch and Hudson, 2007;Anudu et al, 2014), especially in large sedimentary basins, such as the Parnaíba Basin (970 000 km 2 ). To minimize the reduced resolution of airborne data for mapping the basin internal geometry, we introduced seismic and well data, which are the most appropriate geophysical methods for investigations of basin architecture and served to reduce ambiguity in the interpretation of magnetic and gravity data.…”

Investigation of Shallow Structures as The Pathway of Oil Seep in The Alue Punoe Village, Bireuen District, Aceh Province, Indonesia

“…The models produced also were referred to the geology hypothesis about sedimentary fault from (Grauch and Hudson, 2007) that can be seen in Figure 4. After getting anomaly models with which the qualitative information of minor fault can be interpreted quantitatively.…”

Identifying Buried Segments of Active Faults in the Northern Rio Grande Rift Using Aeromagnetic, LiDAR, and Gravity Data, South-Central Colorado, USA

“…Hudson [3] have demonstrated the utility and challenges of using high-resolution aeromagnetic data to interpret shallow normal faults for the central Rio Grande rift. Widespread, partially concealed and totally buried faults that offset Tertiary and younger rift sediments within basins of the central Rio Grande rift are expressed as numerous subtle, northerly trending, linear anomalies.…”

“…Using commonly observed magnetic properties for sediments in the central Rio Grande rift [46], Grauch and Hudson [3] estimate that faults near the surface require at least 30 m of throw to produce the observable aeromagnetic anomalies, indicating that faults with aeromagnetic expression likely have significant vertical displacement. However, not all faults with significant vertical displacement juxtapose layers of differing magnetic properties, even along strike, so that aeromagnetic data may not reveal all faults or the total lengths of individual faults.…”

“…Farther south, in the central Rio Grande rift, aeromagnetic methods have proved useful for mapping intrasedimentary faults under cover [3], but age of activity cannot be determined from aeromagnetic data alone. Although dense vegetation and population are not as widespread as in the Pacific Northwest, active fault scarps can still be difficult to identify because of widespread eolian cover and dynamic weathering.…”