HR: 09:00h
AN: S21A-05    [PDF]
TI: Q Tomography in the Yellowstone Region: Effects of Mantle Water Content
AU: * Adams, D C
EM: dadams@onewest.net
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272 United States
AU: Humphreys, E D
EM: gene@newberry.uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272 United States
AB: Estimation of t* in continental settings is especially hampered by signal-generated noise. To deal with this problem in our study of S-wave attenuation in the Yellowstone-Snake River Plain region, we apply a linearizing filter that estimates the polarization direction of the teleseismic S-wave, and we then remove that portion of the signal whose polarization differs from the estimated direction. We also use two separate methods for estimating t* (spectral ratio and cross-correlation of synthetically attenuated traces) and compare the results. As our main interest is the expression of the mantle "plume" which drives the Yellowstone system, we concentrate on the area beneath Yellowstone and the Snake River Plain, which also is where ray coverage is best. Inversion of data from the linear array across the Snake River Plain and of those for the 2-D Yellowstone array reveal a central upper mantle region of high attenuation (low Q). This is flanked and partially overlain by a region of low attenuation (high Q) that is best expressed to the NW. Beneath Yellowstone Park the low-Q zone extends upward to the base of the crust. If attenuation in this region is controlled more by intracrystalline water content than by temperature, these high-Q regions could represent a cap of depleted, relatively dehydrated residuum overlying hydrous "plume" material. Low-degree partial melting may serve to increase Q by partitioning water into the melt. Some high-Q regions within the cap may reflect such melts. The low-Q region extending to the base of the crust beneath Yellowstone Park may reflect high-degree partial melts where temperature effects or grain-boundary sliding may become important. Diffraction effects may be present in our data but are most likely secondary; areas of most anomalous t* typically occur source-ward of the "plume" and tend not to change polarity for events of opposite back-azimuth.
DE: 5144 Wave attenuation
DE: 7218 Lithosphere and upper mantle
DE: 7294 Instruments and techniques
DE: 8180 Tomography
DE: 9350 North America
SC: Seismology [S]
MN: 2003 Fall Meeting