HR: 13:55h
AN: T53E-02    [Abstracts]
TI: A Multidisciplinary Investigation of Rio Grande Rift Deformation
AU: * Lowry, A R
EM: arlowry@abdu.colorado.edu
AF: Dept Physics, University of Colorado, Boulder, CO 80309-0390 United States
AU: Sheehan, A F
EM: afs@cires.colorado.edu
AF: Dept. Geological Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Roy, M
EM: mroy@unm.edu
AF: Dept. Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Jones, E
EM: esjones@mtholyoke.edu
AF: Dept. Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Nerem, S
EM: nerem@ocelot.colorado.edu
AF: Colorado Center for Astrodynamics Research, University of Colorado, Boulder, CO 80309 United States
AB: The Rio Grande rift is the easternmost actively deforming province of the western margin of North America. Geologic observations suggest the character of rifting changes from north to south, with a narrow rift marked by linear topographic depressions in Colorado and northern New Mexico grading to a broad ``basin and range'' expression in south-central New Mexico. Reasons behind the variable character of the Rio Grande rift are not well-understood, but may have significant bearing on our understanding of how and why continental lithosphere extends and of earthquake and volcanic hazards in rift zones. Copious geophysical data make it an ideal laboratory in which to study the roles of lithospheric rheology, plate boundary forces and local buoyancy in active continental rifting. However, existing data are ambiguous about physical processes, rates and spatial distribution of RGR extension. For example, mantle seismic expression of the rift may be narrow or wide depending on whether one assumes V_p, V_s or Q anomalies as a proxy. Moreover, estimates of strain are imprecise. Geological and geodetic data suggest rates ranging from 0.3 to 5 mm/yr extension. Existing Continuously Operating Reference System (CORS) network GPS sites suggest ~1 mm/yr extension with an additional ~1 mm/yr of left-lateral strike slip, but uncertainties are as large as the signal. In concert with the Plate Boundary Observatory--EarthScope deployment of 20 coarsely (~200 km) spaced continuous GPS in the vicinity of the Rio Grande Rift, we are preparing a focused deployment of 24 quasi-continuous, quasi-campaign GPS sites in five <50 km-spaced profiles that will serve as a platform to address several questions about the nature of continental rifting, including: What seismic hazard does the Rio Grande Rift pose? Is deformation steady or episodic? Does observed Quaternary fault slip agree with geodetic strain rates? How wide is the rift, and how does strain vary along strike? How far north has the Rio Grande Rift propagated? What is the influence of mantle rheology, and how does deformation style depend on strain rate? This presentation will review what we already know about the rift, including the range of hypothetical mechanisms for rifting, and assess what kinds of geodetic information are needed to achieve a better understanding. Recovering signal from such low deformation rates will be challenging. We will discuss progress on site selection, permitting and installation of the network as well as monumentation and occupation strategies. We will also present other advances in data analysis needed to achieve high accuracy estimates of GPS velocity in low-strain-rate locales such as the Rio Grande rift.
UR: http://anquetil.colorado.edu/~arlowry/Rio_Grande_Rift.htm
DE: 1209 Tectonic deformation (6924)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: Fall Meeting 2005