Upper Mantle Structure Beneath the Northern East African Plateau from P- and S-wave Body-wave Tomography
Open Access
- Author:
- Bressers, Cathleen
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 17, 2019
- Committee Members:
- Andrew Arnold Nyblade, Thesis Advisor/Co-Advisor
Charles James Ammon, Committee Member
Christelle Wauthier, Committee Member - Keywords:
- tomography
East African Rift System
AfricaArray
Uganda
Upper Mantle
VanDecar
lithosphere
multi-channel cross correlation
Kenya Rift
East African Plateau - Abstract:
- The AfricaArray NE Uganda Seismic Network was deployed to address the lack of resolution in existing upper mantle body wave tomography models beneath the northern part of the East African Plateau. The nine-station broadband seismic array ran from January 2017 to December 2018. Data from the network were added to an existing body-wave travel times dataset spanning 1985-2015 constructed using data from over 300 seismic stations throughout East Africa. Data from teleseismic earthquakes were used to generate P and S wave travel time residuals using a multichannel cross correlation method and then inverted for Vp and Vs tomographic images of the upper mantle. The resulting models show two new features referred to as Anomaly A and Anomaly B. Anomaly A is a fast wave-speed anomaly (FWA) located in north-central Uganda. The FWA extends from approximately 100 km to 300 km depth, it coincides with the location of the Ugandan Basement Complex, and it extends north of the Aswa Shear Zone (ASZ), indicating that the ASZ disrupts the upper mantle structure. Anomaly A may either be interpreted as the northwestern extension that is part of thick cratonic lithosphere of the Tanzania Craton or else a southeastern extension of the Congo Craton lithosphere. Anomaly B is a low wave-speed anomaly (LWA) in eastern Uganda along the border with Kenya that extends from depths of 100 km to 300 km. From tabular body resolution tests, Anomaly B appears to be an extension of an LWA beneath the Kenya Rift imaged in previous studies. Anomaly B extends beneath the northeastern corner of the East African Plateau away from the rift proper, and may be an extension of the African Superplume, which is upwelling around the thick lithosphere of the Tanzania Craton.