HR: 15:15h
AN: T33E-07    [Abstracts]
TI: Interpreting Crust and Mantle Stress and Strain Indicators at Yellowstone
AU: * Waite, G P
EM: gwaite@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS-910, Menlo Park, CA 94025 United States
AU: * Waite, G P
EM: gwaite@usgs.gov
AF: Dept. of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Smith, R B
EM: rbsmith@mines.utah.edu
AF: Dept. of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Puskas, C M
EM: cmpuskas@mines.utah.edu
AF: Dept. of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Schutt, D L
EM: schutt@uwyo.edu
AF: Dept. of Geology and Geophysics, University of Wyoming, Laramie, WY 82071 United States
AB: Results from several seismic and geodetic studies of the Yellowstone hotspot crust and mantle are integrated to derive a consistent interpretation. Mantle seismic tomography and anisotropy were determined using data recorded at two temporary arrays of IRIS-PASSCAL seismographs deployed in a 400 km (NE-SW) by 500 km (NW-SE) area centered on Yellowstone, combined with data from the U.S. National Seismograph Network and the University of Utah Seismograph Stations' permanent network. Teleseismic tomography reveals a low velocity anomaly in the mantle beneath the 0.63 Ma Yellowstone caldera to a depth of 200 km of up to -2.3% V$_{P}$ and -5.5% V$_{S}$. The low velocity zone is elongated NE-SW, parallel to the direction of absolute plate motion (APM), from the edge of the tomographic model in the SW to 75 km beyond the caldera to the NE. Anisotropic seismic fast directions from teleseismic shear-wave splitting are generally parallel to the direction of APM, but rotate up to 80\deg from APM at stations within and adjacent to the caldera. The splitting fast axes are inconsistent with olivine lattice preferred orientation due to a broad parabolic flow pattern that might be predicted for a hotspot plume at the base of a moving plate. Instead, stress-oriented, partial melt-filled lenses in the lithosphere could be responsible for splitting fast axes that are perpendicular to the plate motion. Focal mechanisms of local earthquakes, which occur in the upper 10 km of the crust, were used to estimate the stress field orientation. Local earthquake data have also been used to make new shear wave splitting measurements. The crustal splitting measurements are consistent with anisotropy due to stress-oriented crustal cracks. The direction of minimum horizontal stress is N-S in the E-W band of high seismicity north of the caldera, but rotates to NE-SW in the center of the caldera. GPS-derived strain is also consistent with this N-S to NE-SW rotation. Yellowstone is at the NE edge of the Basin and Range province, which is undergoing NE-SW extension in that area. Continued NE migration of the hotspot, as indicated by the mantle low velocity zone, may be driving localized expansion of the extensional regime. The rotation of crustal stress and strain at Yellowstone may reflect the NE migration of the edge of the Basin and Range.
DE: 7230 Seismicity and seismotectonics
DE: 7280 Volcano seismology (8419)
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting