Stanford University
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Steve Gao, MUST, A Synthesis of 10 Years of Geophysical Research on the East African Rift System

When:
Thursday, Oct 24, 2019 12:00 PM
Where:
Mitchell 350/372
Audience:
Faculty/Staff, Students, Alumni/Friends
Sponsor:
Geophysics Department

Steve Gao

Geology and Geophysics Program, Missouri University of Science and Technology

Title: New Insights into the Initiation and Development of Continental Rifts: A Synthesis of 10 Years of Geophysical Research on the East African Rift System

Host: Simon Klemperer (sklemp@stanford.edu)

To investigate rifting structure and dynamics especially the existence and depth extent of previously-proposed active thermal upwelling beneath the youngest (Okavango and Malawi) and most developed (Afar) sections of the East African Rift System (EARS), we deployed about 70 broadband seismic stations in five countries along four profiles with a total length of ~2500 km between 2010 and 2014 using NSF and Statoil funding. Analyses of these and other available data sets using an array of seismological techniques, such as shear wave splitting, receiver function imaging for the Moho and the 410 km and 660 km discontinuities bordering the mantle transition zone (MTZ), and seismic body and surface wave and ambient noise tomography, reveal various new characteristics in the crust and mantle beneath the EARS. For instance, stacking of receiver functions under the non-plane wave assumption demonstrates a general absence of high temperature anomalies in the MTZ, an observation that is inconsistent with the present-day presence of mantle plumes beneath the sampled regions of the EARS. Additionally, shear wave splitting analysis suggests that there is no localized anomaly in the mantle flow field beneath the investigated segments of the EARS.  These results, together with the observation that the vast majority of the world’s Cenozoic rifts were developed in previous orogenic belts which are zones of mechanical weakness and sudden changes in lithospheric thickness, suggest that rifting can be initiated and maintained by lateral variations in horizontal stress applied to the base of the lithosphere in places with sudden changes in lithospheric thickness.

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