HR: 08:00h
AN: S11E-01    [Abstracts]
TI: Shear-Wave Structure Beneath Southern Africa From Rayleigh Wave Tomography
AU: * Li, A
EM: ali2@mail.uh.edu
AF: University of Houston, 4800 Calhoun Rd, Houston, TX 77204 United States
AB: Southern Africa is characterized by the Archean Kaapvaal and Zimbabwe cratons with several Proterozoic mobile belts surrounding them. To investigate the evolution of the cratons, we have analyzed Rayleigh wave data recorded at the Southern Africa Seismic Experiment, which consisted of 82 broadband seismic stations and operated from April 1997 to July 1999. A two-plane-wave inversion technique is adopted in this study to account for the non-planar energy in the incoming wave field. Average phase velocities are obtained at 14 periods ranging from 20 s to 100 s and vary from 3.65 km/s at 20 s to 4.11 km/s at 50 s and 4.22 km/s at 100 s. These values agree well with Rayleigh wave phase velocities in the Kaapvaal craton in a global model. Fast anomalies at wavelengths of 200-400 km are imaged in the Kaapvaal and Zimbabwe cratons at periods less than 45 s and low velocities appear in the Bushveld-Complex province and the nearby mobile belts. At longer periods, high velocities on relatively small scales are observed both within and outside the cratons, suggesting that the cratonic lithosphere might have been eroded at great depths due to small-scale mantle convections. The lowest velocity is found under the Namaqua-Natal and Cape-Fold belts, the youngest region in the study area. We will resolve the 3-D shear-wave structure from these phase velocities and discuss the dynamics of the cratonic lithosphere in southern Africa.
DE: 9305 Africa
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting