Shear Wave Structure and Radial Anisotropy beneath the Tanzania Craton

The Archean Tanzania craton, a segment of old continental lithosphere, is situated within the African superswell, which has been primarily believed to be plume-supported, and is surrounded by Proterozoic mobile belts which are disrupted by the Cenozoic East African rift system. It provides a unique opportunity to test the stability of Archean cratonic lithosphere and compare models and observations in an active tectonic province which has been affected by magmatism, uplift, active extension and rifting.

Vertical and transverse component seismograms from 90 events at 61 stations were filtered at 18 centre frequencies with a narrow bandwidth of 10 mHz with centre periods ranging from 20 to 166 s. These fundamental mode Rayleigh wave and Love wave data from the TBSE and AfricaArray networks are modeled for regional-average dispersion and 2-D phase velocity maps, employing the two-plane-wave tomography method while accounting for finite frequency effects. The structural variation with depth is explored by inverting the resulting phase velocity dispersion curves to obtain the shear wave velocity structure of the crust and upper mantle. 3-D, radially anisotropic velocity models are obtained for the first time for the region, by jointly inverting Love and Rayleigh wave phase velocities. The discrepancy between SV and SH velocity structure indicates the presence of radial anisotropy, which will be interpreted in terms of mantle flow from the African superplume, fossil anisotropy in the lithosphere, and shape-preferred orientation anisotropy in magmatic regions of the East African rift system.

The results will be compared with the Wyoming craton, which has experienced episodes of lithospheric rejuvenation and delamination in the past and present, facilitating characterization of the various geotectonic mechanisms interacting with the cratons and with each other.