Uppermost mantle P-wave velocity structure of the Main Ethiopian Rift

Open Access
Author:
Rouse, Stewart Desmond
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 02, 2010
Committee Members:
  • Andrew Arnold Nyblade, Thesis Advisor
Keywords:
  • Ethiopia
  • Main Ethiopian Rift
  • East Africa
  • Pn tomography
Abstract:
Although the Main Ethiopian Rift (MER) has been studied extensively over the past decade, little is known about the crust and mantle beneath its southern part. In this study, we investigate the upper mantle velocity structure of the MER with a focus on the uppermost mantle beneath the southern Main Ethiopian Rift. We use seismic data from the 27-station Ethiopian Broadband Seismic Experiment and the 29-station Ethiopian Afar Geoscientific Lithospheric Experiment to obtain Pn travel times for ~300 local and regional events. The Pn travel times have been inverted for Pn velocities using a standard singular value decomposition method, and the results show a low velocity zone in the uppermost mantle beneath both the northern Main Ethiopian rift (NMER) (7.4-7.5 km/s) and SMER (7.5-7.7 km/s). In contrast, an area of higher velocities is found under the central Main Ethiopian rift (CMER) (7.7-7.9 km/s). We suggest that the lower Pn velocities in the SMER and NMER compared to the CMER result from greater amounts of crustal thinning, which results in an increase in the modification of the uppermost mantle. The greater amounts of crustal thinning can in turn be attributed to the greater duration of extension in the SMER and NMER compared to the CMER.