HR: 0800h
AN: G51C-0854    [Abstracts]
TI: Active salt tectonics in the Needles District, Canyonlands (Utah) detected by Interferometric SAR and Point Target Analysis: 1992-2002
AU: * Furuya, M
EM: furuya@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 1130032 Japan
AU: * Furuya, M
EM: furuya@eri.u-tokyo.ac.jp
AF: Department of Physics and CIRES, University of Colorado, CB390, Boulder, CO 80309-390 United States
AU: Mueller, K
EM: karl.mueller@colorado.edu
AF: Department of Geological Sciences, Univesity of Colorado, CB399, Boulder, CO 80309-399 United States
AU: Wahr, J
EM: wahr@longo.colorado.edu
AF: Department of Physics and CIRES, University of Colorado, CB390, Boulder, CO 80309-390 United States
AB: The Needles District in Canyonlands National Park, Utah, is located southeast of the confluence of the Colorado and Green Rivers, and includes elongate, extensional fault blocks that have accommodated flexure of a thin sequence of sedimentary rock. Faults are produced by gravity-driven extension and downward flexure of a thin, overlying sandstone plate into the Colorado River canyon. Strain is driven by dissolution and flow of underlying halite and gypsum (salt). Previous numerical studies successfully reproduce a number of field geological observations [ Schulz-Ela and Walsh,~2002; Walsh and Schultz-Ela,~2003]. It remains uncertain, however, how to relate strain currently being accommodated to the longer-term strain history of the region. To understand how short-term processes combine to generate geologic structures, we used InSAR to search for ongoing, decadal ground displacements. Here we report our observational results derived by applying both the standard InSAR analysis and the Interferometric Point Target Analysis (IPTA) by Werner et al.~[2003] (similar to the Permanent Scatterer technique). Although Marsic et al.~[2003] had previously applied standard InSAR technique to the Needles, our study extends their results by including additional scenes acquired over a longer time period and by using IPTA. Our results show that most of the Needles is indeed subsiding now at a maximum rate of 2-3 mm/year. The deforming region is almost totally restricted to east of the Colorado River. We observe strain patterns that were previously undetected. These include a region with little surface extensional strain in the southwestern part of the deforming region, that is subsiding at higher rates than anywhere else in the Needles. This area is bounded by the Colorado River canyon, a rapidly subsiding, east-west trending graben to the south, and a diffuse strain gradient to the east. Rates of subsidence are lower further north, in a region of spectacularly exposed fault blocks that have been previously studied in detail. We see no systematic difference is subsidence rates in single grabens in the northern part of the Needles, except for an abrupt strain gradient at the easternmost normal faults in the array. Some grabens do show patterns of subsidence that hint at higher fault slip rates in the centers of linked fault arrays. However definitive documentation of this pattern awaits a more detailed error analysis and inclusion of additional orbit tracks. Our analysis has also revealed the presence of narrow regions of active uplift, at rates of 2-3mm/yr, located along the eastern bank of the Colorado River adjacent to the array of active normal faults. We interpret these as recording active diapiric uplift. Interestingly, while the subsiding motion is mostly linear and does not temporally fluctuate, the uplifting region shows large temporal fluctuations that may be related to short pulses of uplift at annual scales. While our analysis has answered some long-standing questions about the Needles, it is also significant for measuring very low amounts of total strain along active geologic structures. For instance, our work suggests it is possible to use InSAR to map detailed variations in subsidence or uplift of less than 3 cm of ground displacement using long-term data sets.
DE: 1209 Tectonic deformation (6924)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8109 Continental tectonics: extensional (0905)
SC: Geodesy [G]
MN: Fall Meeting 2005