ASSESSING LATE QUATERNARY DEFORMATION ACROSS THE SOUTHERN RIO GRANDE RIFT WITH THE USE OF HIGH-RESOLUTION PHOTOGRAMMETRY

The southern Rio Grande rift (RGR) is an area of ongoing extension, recorded by fault scarps cutting late Quaternary geomorphic surfaces and by GPS geodesy. Extension in the southern RGR is more diffuse than in the north and can be distinguished from the larger Basin and Range province to the west by certain characteristics such as higher heat flow and more recent faulting. Evidence of recent fault activity suggests the potential for continued deformation and significant seismic events.

This work will present progress toward assessing slip rates of three range-bounding normal faults (Caballo, San Andres and Alamogordo) across the southern RGR as estimated by the use of high-resolution topographic surveying. Structure from Motion (SfM) photogrammetry of well-preserved geomorphic surfaces offset across the Caballo and Alamogordo faults will be presented in detail. Correlation of geomorphic surfaces is achieved by making comparisons between soil development, clast strength and morphologic ages of fault scarps and terrace risers.

The Caballo and Alamogordo faults are easily recognizable in aerial photography and low-resolution (10 m) digital elevation models (DEMs) available for the area as N-S trending scarps across multiple generations of alluvial surfaces. Though the faults can be identified with low-resolution DEMs, meaningful measurements of late Quaternary displacement cannot be derived given that the scale of offsets is often near what can be resolved at the 10 m scale. The SfM technique is used to create a high-resolution (cm scale) DEM of the study area to more accurately assess the magnitude of slip in late Quaternary time and to make a comparison with total extension possible in future work.

Late Quaternary slip rates will be compared to overall extension since late Paleogene initiation, to be derived from a balanced cross-section along an E-W transect of the rift, in future work. Slip rate estimations will also allow for comparison to interseismic deformation rates as recorded by GPS monitoring across the broader region. Ages of fault-exposed surfaces will be more precisely estimated by the measurement of cosmogenic nuclide accumulation. The work presented, and that planned for the future, will provide additional insight into how intracontinental rifting progresses.