Receiver function studies of crustal structure, composition, and evolution beneath the Afar Depression, Ethiopia
"The dissertation utilizes a set of sophisticated computer programs developed at the Geophysics group at Missouri S&T to characterize crustal properties beneath the Afar Depression in Ethiopia where extensional tectonics dominates. In this study, measurements of crustal thickness (H), crustal mean Vp/Vs [which is related to Poisson's ratio (Σ)], and the sharpness of the Moho (R) were determined using teleseismic data from 18 broadband seismic sensors that we deployed along a profile of 250 km long with a station spacing of ~ 10 km. The stations had been recording continuously for an entire year from December 2009 until December 2010. The measurements were determined by stacking P-to-S converted waves (PmS) and their multiples (PPmS and PSmS). Results suggest that the average crustal thickness beneath the Afar Depression is about 28.56±0.28 km and the crust is characterized by large Vp/Vs of 1.93±0.017 and smaller-than-normal overall stacking amplitude of the P-to-S converted phases beneath most stations. Our results suggest that the crust beneath the entire study area is significantly thinned and extensively intruded by mafic dikes, representing a transitional stage between continental and ocean crust. The Tendaho Graben has the thinnest and most mafic crust, which is also supported by the observation of gravity data which suggest that the active magmatic areas are characterized by higher gravity anomalies while the thicker crusts have smaller and negative anomalies. Thus, the crust beneath the center of the Tendaho Graben is likely to be oceanic-type, and becomes progressively more continental away from the center"--Abstract, page iii.
Missouri University of Science and Technology
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