Active Deformation at Canyonlands National Park: Distribution of Displacement Across Grabens Using InSAR

The Needles District of Canyonlands National Park in southeastern Utah is a unique geologic region in which active extensional tectonics can be observed. The arcuate, northwest-trending system of faults that define the grabens region of the Needles District have simple stratigraphy and excellent exposure, therefore permitting the study of normal faults under relatively simple conditions. A 460 meter-thick sedimentary section is underlain by the Paradox evaporites, all of which sits within western flank of the Monument Uplift. It is generally accepted that once the adjacent Colorado River downcut into the Paradox Member, the sedimentary sequence became unbuttressed, and was consequently allowed to slide along the northwest dip of the Monument Uplift's western flank. Using satellite radar interferometry (InSAR) and the Global Positioning System (GPS), we are monitoring recent deformation across the graben system. Prior to our study, knowledge of Canyonlands deformation rates was limited to long term geologic averages. We use synthetic aperture radar data collected by the ERS-1 and ERS-2 satellites encompassing a 7 year period of observation (1992-1999). We have produced 10 successful interferograms with short baselines (< 100 m) from both ascending and descending orbital trajectories. Preliminary results indicate regional subsidence within the graben system. The interferograms show surface deformation in the grabens as great as 3 mm/yr. in the look direction of the satellites, with greatest displacements occurring primarily in the northwestern portion of the region. InSAR derived rates are consistent with previously published results. Individual graben bounding faults can be resolved in many interferograms and we can resolve the spatial distribution of deformation across the graben system. Transects across the interferograms show a distribution of displacement rates that decreases to the east. Prior research has demonstrated that within the grabens there is a general eastward decrease in graben age and complexity, in addition to an increase in bounding fault asymmetry. Our work allows us to compare these observations with current displacement rates.