HR: 1340h
AN: T23A-0533    [Abstracts]
TI: Observations of Asthenosphere From Regional Rayleigh Wave Tomography
AU: * Li, A
EM: ali2@uh.edu
AF: University of Houston, 4800 Calhoun Rd, Houston, TX 77204
AB: Asthenosphere is defined as a weak, plastic layer in the earth's upper mantle under the rigid lithosphere and can be observed as a low velocity zone in seismic velocity models. We have performed Rayleigh wave tomography and constructed 3-D shear-wave velocity models in Iceland, southern Africa, and eastern North America. The comparison among these models indicates that the velocity and the depth range of the low velocity zone vary significantly from oceans to continents. A low velocity zone is consistently imaged beneath Iceland with the shear-wave velocity of 3.85 km/s to 4.05 km/s at the depths of 60 to 120 km. In southern Africa, we have observed a much weaker low velocity zone across the entire study region at the depths of 160 to 260 km. Shear-wave velocity in this zone varies from 4.45 km/s at the southern and eastern margins of southern Africa and to 4.65 km/s underneath the central part of the Kaapvaal craton. In eastern North America, a low velocity zone is not continuously imaged in the upper mantle. The depth range of the low velocity zone is from 70 to 120 km at the Atlantic margin and from 100 to 260 km at some places of the eastern North America craton. These observations suggest that the asthenosphere beneath the continents is much weaker, more complex, and at greater depths than beneath the oceans.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: Fall Meeting 2005