HR: 0830h
AN: S51C-0056    [PDF]
TI: Seismic Structure of the African Upper Mantle Determined from Multi-Mode Rayleigh Waveform Inversion
AU: Debayle, E
EM: eric_debayle@ulp-strasbg.fr
AF: CNRS and EOST, ULP, 5 rue Rene Descartes, Strasbourg, 67084 France
AU: * Priestley, K
EM: keith@esc.cam.ac.uk
AF: Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB30EZ United Kingdom
AU: Pilidou, S
EM: pilidou@esc.cam.ac.uk
AF: Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB30EZ United Kingdom
AB: We present a high-resolution shear wave velocity model of the African upper mantle based on waveform analysis of a large fundamental and higher mode Rayleigh wave data set. Our model is derived from all data currently available from permanent seismographs and temporary field experiments in the region. This allows us to restrict our analysis primarily to short epicenter-station paths ($<$ 6000 km) and minimizes spurious effects such as multipathing or focusing/defocusing while still achieving high path density. In addition, the analysis is undertaken at relatively long period ($\sim$50-160 s) with a small number of higher modes (up to the fourth) to avoid artifacts due to the neglect of mode coupling while still preserving good resolution in the whole upper mantle. The dense path coverage, wide azimuthal distribution, substantial higher mode content, and short path length of the data set enable us to build an upper mantle model for the region with a horizontal resolution of a few hundred kilometers extending to $\sim$400 km depth. The resulting model confirms that the high velocity lid associated with African cratonic roots is relatively thin extending to 180-200 km depth beneath southern Africa and $\sim$250 km beneath west Africa. The cratons are generally delimited by sharp boundaries. Eastern Africa is underlain by a well-resolved deep low velocity anomaly that extends from shallow depth beneath Afar to at least the transition zone suggesting deep upwelling with a possible connection with the tilted lower mantle, low velocity anomaly that has been observed in the global tomographic results. Some other Africans hotspots seem however, to have a shallower origin that could involve other processes such as small-scale convection in the upper mantle.
DE: 1010 Chemical evolution
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8109 Continental tectonics--extensional (0905)
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting