MONITORING ACTIVE DEFORMATION IN THE GRABENS OF CANYONLANDS NATIONAL PARK

The Grabens of Canyonlands National Park in southeastern Utah have excellent exposure, simple stratigraphy, and young deformation. The fault system at Canyonlands is a sort of "geologic-scale sand box experiment," permitting the study of normal faults under relatively simple conditions. A 500 meter-thick sedimentary section is underlain by the Paradox evaporites. Faulting at Canyonlands began when the Colorado River cut through the sedimentary section to the level of the evaporites. This released the retaining buttress on the western margin of the Canyonlands region, and the overlying sedimentary section began to slide toward Cataract Canyon. Many researchers have examined normal fault processes in the Canyonlands through detailed field observations, and analog and numerical modeling. The long-term rate of extension is estimated to be between 2 mm/yr and 2 cm/yr across the fault system, and deformation is on-going. We report on precise measurement of the modern rate and direction(s) of extension to enable rigorous interpretation of the field data and provide tests of model results.

We are using GPS and satellite radar interferometry (InSAR) to monitor recent and continuing deformation across the graben system. Field work in the summer of 2000 established a network of GPS benchmarks across the fault system in 2 orthogonal transects. Initial reoccupation in 2001 did not yield a deformation signal above noise. At this meeting, we will report results of our second reoccupation (planned for September 2002).

For InSAR, we use synthetic aperture radar data collected by the ERS-1 and ERS-2 satellites over the last decade. We have produced several successful interferograms with short baselines (less than 100 m) from both ascending and descending orbital trajectories. The interferograms show surface deformation in the grabens as great as 1 cm/yr in the look direction of the satellites. The magnitude of this change exceeds DEM error by an order of magnitude. GPS results will be used to derive horizontal and vertical velocities from the interferograms. Transects across interferograms show a distribution of strain rate that is consistent with published results of numerical models for the Canyonlands grabens.