HR: 17:15h
AN: S52J-06    [PDF]
TI: Upper Mantle Seismic Velocity Structure beneath East Africa and the Arabian Peninsula
AU: * Benoit, M H
EM: mbenoit@geosc.psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802 United States
AU: Nyblade, A A
EM: andy@geosc.psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802 United States
AU: Pasyanos, M
EM: pasyanos1@llnl.gov
AF: Lawrence Livermore National Lab, L-205 P.O. Box 808, Livermore, CA 94551 United States
AU: VanDecar, J C
EM: vandecar@dtm.ciw.edu
AF: Carnegie Institution of Washinton, 5251 Broad Branch Road NW, Washington, DC 20015 United States
AB: The origin of Cenozoic tectonism in East Africa and the Arabian Peninsula remains enigmatic. Previous studies suggest that the existence of slow seismic velocities, that may extend into the lower mantle, are related to the tectonism. To further evaluate the origin of the tectonism, we investigate the depth extent of the anomalous seismic velocities. Using data collected from IRIS/PASSCAL broadband seismic experiments and permanent stations located in East Africa and the Arabian Peninsula we measure surface wave group velocity dispersion curves and tomographically invert them to constrain crustal and upper most mantle seismic velocities. Additionally, we use P and S wave body wave tomography to examine the upper mantle seismic velocity structure beneath Ethiopia. The Rayleigh and Love wave group velocities maps that we computed show the major tectonic features in the region. The short period maps (10-40s) resolve crustal features such as sedimentary basins, differences between continental and oceanic crust, and regions of crustal thickening and thinning. Longer period group velocity maps (50-80s) reveal anomalously slow velocities in the upper mantle beneath rifted and tectonically active regions, while also resolving fast, stable features like the Tanzania Craton. Though surface wave data can resolve lithospheric structure, body wave data is needed to resolve deeper structure. Results from the body wave tomographic study beneath Ethiopia shows a low velocity zone located in the upper mantle beneath the Afar triangle and rifted portion of the country. Additionally, the western half of the Ethiopian Plateau was underlain by slower seismic velocities then beneath the eastern half of the Plateau. Though the low velocity zone appears to extend into the transition zone, there is significant vertical smearing in our results, and resolution tests suggest that the low velocities are confined to the depths shallower than 400 km.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8180 Tomography
SC: Seismology [S]
MN: 2003 Fall Meeting