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. 1. Introduction The combination of aeromagnetic methods and LiDAR (Light Detection And Ranging) mapping has proved useful for identifying active faults in dynamically deforming, compressional terranes in the Pacific Northwest region of USA [1, 2]. Linear aeromagnetic anomalies and gradients corresponding to thrust and tear faults are associated with fault scarps on the ground, located by airborne LiDAR surveys. The scarps are otherwise difficult to identify in the highly populated areas and under widespread, dense vegetative cover. Recent acquisition of aeromagnetic and airborne LiDAR data over the northern Rio Grande rift in the southwestern USA has afforded the opportunity to test these methods in a less active, extensional basin in a semiarid environment. 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. Thus, combined analysis of high-resolution aeromagnetic data and LiDAR images builds on the strength of the aeromagnetic method to locate normal
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