Southern Africa upper mantle

Fig. 8. Three-component waveform fits at three distance ranges for synthetic seismograms (dotted lines) computed from composite velocity model consisting of the seismic lithosphere of the southern African model of Priestley (1999) above 160 km depth and the southern Africa upper-mantle model derived from the global tomographic model S12WM13 below 160 km depth compared with the observed seismograms (continuous lines) of the 14 August 1994 earthquake (Fig. 1, event 8) recorded at three distance ranges.

James D. E., Boyd E. R., Bell D., and Carlson R. (2001) Xenolith constraints on seismic velocities in the upper mantle beneath southern Africa. Abstracts of the Slave-Kaapvaal Workshop A Tale of Two Cratons, Merrickville, Ontario, Canada, 2pp. 

The Kaapvaal Project was vmdertaken to study the formation, stabilization and evolution of cratons, and to image the deep structure of the tectosphere (Carlson et al. 1996) (see also http // www.ciw.edu/kaapvaal for participants and a description of the project). A cornerstone of the Kaapvaal Project was a large-scale broadband seismic experiment designed specifically for geo-logical-scale imaging of the crust and upper mantle beneath the cratons and adjacent Proterozoic provinces of southern Africa (Fig. 1). The... 

Gore, J. 2002. Seismological structure of the crust and upper mantle of the Zimbabwe craton and Limpopo belt, southern Africa. PhD thesis. University of Zimbabwe, Harare. 

James, D. E., Carlson, R. W., Boyd, F. B. Janney, P. E. 2001a. Petrologic constraints on seismic velocity variations in the upper mantle beneath southern Africa. EOS Transactions, American Geophysical Union, 82(20, Abstract Suppl.), S247. 

Priestley, K. 1999. Velocity structure of the continental upper mantle evidence from southern Africa. Lithos, 48, 45-56. 

Zhao, M., Langston, C. A., Nyblade, A. A. Owens, T. J. 1999. Upper mantle velocity structure beneath southern Africa from modeling regional seismic data. Journal of Geophysical Research, 104, 4783-4794. 

The structure of the upper mantle beneath southern Africa... 

McWilliams 1977). Qiu et al. (1996) used earthquakes in southern Africa recorded at stations in Zimbabwe and South Africa (Fig. 1) to obtain an average velocity model for southern Africa. The main features of their model are a high shear-wave velocity lid in the upper mantle shown by both seismic and petrological data, below which there is a decrease in the shear-wave velocity shown by the seismic data. Priestley (1999) reexamined the seismograms studied by Qiu et al. (1996) and included additional data to determine... 

Fig. 3. (a) Sensitivity test of the higher-mode waveforms to the depth to the base of the upper-mantle lid for the SLR seismogram of the 18 July 1986 earthquake (Fig. 1, event 2). The continuous line is the observed waveform, the dotted line is the synthetic for the southern Africa velocity model of Qiu et al. (1996), and the dashed line is the synthetic for the same velocity model but with the lid base increased to the depth indicated at the left of each seismogram, (b) Same as (a) but for the SLR seismogram of the 10 March 1989 earthquake (Fig. 1, event 5). (c) Same as (a) but for the SUR seismogram of the 24 July 1991 earthquake to the minimum S-wave velocity of the low-velocity zone (LVZ). 

Recent work in southern Africa has focused on developing a teleseismic travel time tomography image for the upper mantle (James et al. 2001 James Fouch 2002). The objective of teleseismic travel time tomography is to determine a 3D seismic image for a volume of Earth beneath the seismie array based on the arrival times from a large number of source-receiver combinations. The 3D model is normally expressed in terms of perturbations to a reference model in which the velocity is a function only of radius, where the 3D perturbations account for that part of the travel time not explained by the reference model. 

Bloch, S., Hales, A. L. Landisman, M. 1969. Velocities in the crust and upper mantle of southern Africa from multi-mode surface wave dispersion. Bulletin of the Seismological Society of America, 59, 1599-1629. 

Priestley, K. McKenzie, D. 2002. The structure of the upper mantle beneath southern Africa. In Fowler, C. M. R., Ebinger, C. J. Hawkesworth, C. J. (eds) The Early Earth Physical, Chemical and Biological Development. Geological Society, London, Special Publications, 199, 45-64. 

Woodland, A.B. and Koch, M., 2003. Variation in oxygen fugacity with depth in the upper mantle beneath the Kaapvaal Craton, southern Africa. Earth Planet. Sci. Lett., 214, 295-310. 

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