HR: 1340h
AN: S53B-0224    [Abstracts]
TI: High-Resolution Tomography of the Kaapvaal Craton
AU: * Chevrot, S
EM: Sebastien.Chevrot@cnes.fr
AF: Observatoire Midi Pyrenees, 14 Avenue Edouard Belin, Toulouse, 31400 France
AU: Zhao, L
EM: zhaol@usc.edu
AF: Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740 United States
AB: We present the results of a tomographic study using the broadband waveforms recorded by the Kaapvaal Seismic Array deployed in Southern Africa between 1997 and 1999. The Kaapvaal array is composed of about 80 stations at an average spacing of ~100 km. We accurately measure the phase delays between the different stations using a waveform cross-correlation method. For each event, we compute and subtract the average of all the measurements to reduce the effect of structures outside the array. The dataset is composed of phase delays of broadband {\it{SH}} waves as well as narrowband Rayleigh waves at a number of frequencies between 0.01 Hz and 0.04 Hz. A crustal correction is applied to the phase-delay measurements before they are inverted using an LSQR algorithm. We use a normal-mode coupling method to compute the Fr{\'{e}}chet (sensitivity) kernels for the Rayleigh waves and a normal-mode-ray-theory hybrid approach to compute the kernels for the {\it{SH}} waves. This hybrid approach is adopted to ensure both the efficiency of the calculations with a 10-km grid spacing for the {\it{SH}} waves and the accuracy of the kernels in the near and intermediate fields from the seismic stations. The resulting shear-wave speed model has similar patterns to the shear-wave model for the Kaapvaal region (James et al. 2001) but covers a broader area. The wave-speed anomalies show good correlation with surface geology, in particular with the limits of the cratonic blocks. The upper mantle beneath the Kaapvaal craton is characterized by high wave speed reaching at least 300-km depth. One of the interesting features of our model is a low-speed region in the upper mantle to the east of the Kimberley Array which coincides with the suture between the Witwatersrand and the Kimberley blocks.
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting