Initial results of receiver function analysis across the Ethiopian Plateau: Where does the broad deformation end?

Abstract:

Existing seismic, geodetic and numerical analyses indicate that continental rifting in Ethiopia may include both localized shallow deformation, and deeper, distributed deformation, controlled by the mechanics of the continental lithosphere. To map the thickness and structure of the Ethiopian lithosphere throughout the region of deformation, a temporary broadband seismic network was deployed to expand the aperture of previous geophysical investigations around the Main Ethiopian rift. The Ethiopian Seismic Highland Investigation (ESHI) includes 26 stations on the Ethiopian Highlands as far west as the Sudanese border, and 4 stations on the Somali Plateau.

Here we report on the initial results of the analyses of teleseismic earthquakes recorded by the ESHI network between April 2014-2015. First-order crustal structure beneath the Ethiopian Highlands is inferred from radial receiver functions across the network. By examining stations located radially outward from the rift axis we observed a reduction in arrival time of the P-SV converted phase associated with the base of the crust. These P-SV arrivals are observed between 3.5 – 5.5 s following the direct P onset. The smaller values correspond to stations closer to the Sudanese border, with larger values corresponding to stations closer to the rift axis on the Ethiopian Plateau. The observations agree with previous receiver function studies that sampled similar regions of the Ethiopian Highlands.

These results suggest differences in the thickness or composition of the crust away from the rift axis across the plateau. We are modeling thickness and Vp/Vs ratios to provide initial constraints on crustal thickness and composition of the lithosphere, in which the Main Ethiopian Rift has formed.