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

Abstract

Combined interpretation of aeromagnetic and LiDAR data builds on the strength of the aeromagnetic method to locate normal faults with significant offset under cover and the strength of LiDAR interpretation to identify the age and sense of motion of faults. Each data set helps resolve ambiguities in interpreting the other. In addition, gravity data can be used to infer the sense of motion for totally buried faults inferred solely from aeromagnetic data. Combined interpretation to identify active faults at the northern end of the San Luis Basin of the northern Rio Grande rift has confirmed general aspects of previous geologic mapping but has also provided significant improvements. The interpretation revises and extends mapped fault traces, confirms tectonic versus fluvial origins of steep stream banks, and gains additional information on the nature of active and potentially active partially and totally buried faults. Detailed morphology of surfaces mapped from the LiDAR data helps constrain ages of the faults that displace the deposits. The aeromagnetic data provide additional information about their extents in between discontinuous scarps and suggest that several totally buried, potentially active faults are present on both sides of the valley.

Evidence of Structural Facts Inferred from Aeromagnetic Data Analysis over the Guider-Maroua Area (Northern Cameroon)

“…The presence of linear horizontal gradient magnitude ridges that coincide in some places with the linear topographic scarp provides support for a tectonic origin [32]. The narrowness of the horizontal gradient magnitude ridges advocates near-surface and near-vertical boundaries for the magnetic sources [32]; their linearity supports a fault contact rather than a facies change [31]. As shown on the FVD map (Figure 4), the horizontal gradient magnitude also shows many magnetic lineaments interpreted as faults or magnetic intrusive bodies.…”

“…This map reveals structural features such as folds and faults affecting the basement. The different structural features were recognised by differences in the patterns (such as general orientation and arrangement) of faults inferred [31]. The horizontal gradient magnitude suggests that some faults have significant displacement at depth.…”

Introduction: The View from Blanca Peak

“…Young rift faults are relatively rare along the hingeline on the western margin of the basin. Documented examples include a swarm of faults in the foothills west of Monte Vista and faults in the narrow northernmost end of the Valley (Lipman 1976;Kirkham and Rogers 1981;Widmann et al 1998;Grauch and Ruleman 2013).…”

Geophysical expression of buried range-front embayment structure: Great Sand Dunes National Park, Rio Grande rift, Colorado

“…Aeromagnetic data elsewhere along the range front provide evidence for significant fault offsets along concealed structures located basinward of the range-front fault zones. Along the Crestone section north of the study area, aeromagnetic lineaments are interpreted to reflect a down-to-the-southwest normal fault zone subparallel in trend to the range-bounding fault zone, but located ~5 km to the southwest (Grauch et al, 2012;Grauch and Ruleman, 2013). South of the study area, the Blanca piedmont fault zone is generally along the range front and interpreted as a set of synthetic, subparallel normal faults located 2-3 km west of the range-front fault zone (Fig.…”

“…Due to paleoseismic events and young sedimentary cover that conceals significant parts of the fault zones, surficial fault traces are discontinuous or terminate at active surficial process bound aries such as dune margins and creeks. The concealed extents of discontinuous fault traces have been mapped successfully using high-resolution aeromagnetic surveys in several areas of the Rio Grande rift (Grauch and Drenth, 2009;Grauch and Ruleman, 2013), but interpretation of such surveys is hindered where topographic features composed of magnetic sediments, such as sand dunes, cause interference (Grauch and Hudson, 2007).…”