HR: 16:30h
AN: S52J-03    [PDF]
TI: Crustal Velocity Structure Across the Main Ethiopian Rift
AU: * Mackenzie, G D
EM: gdm1@le.ac.uk
AF: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AU: Thybo, H
EM: thybo@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oester Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Maguire, P K
EM: pkm@le.ac.uk
AF: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AU: Mammo, T
EM: tmammo@hotmail.com
AF: Department of Geology \& Geophysics Addis Ababa University, PO Box 1176, Addis Ababa, ; Ethiopia
AU: Khan, M A
EM: mak@le.ac.uk
AF: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AB: As part of the project EAGLE (the Ethiopia Afar Geophysical Lithospheric Experiment) a 400 km NW-SE wide-angle reflection/refraction seismic profile, was recorded across the Main Ethiopian Rift in January 2003. Instruments were deployed at a nominal spacing of 1 km and consisted primarily of single component Reftek "Texan" recorders with 3 component Guralp CMG-6TD seismometers deployed every 4 - 5 km. Eight in-line borehole shots and eleven fan shots of between 1 and 2 tonnes were recorded over a 4-day period. The data show good energy propagation along the entire length of the profile with a wide coverage of Pg, PmP and Pn phases plus at least one intra-crustal reflected phase. Considerable variation is observed in the amplitude of the reflected Moho and intra-crustal phases across the entire length of the profile. We present preliminary 2D velocity models of the lithospheric structure of the rift from the modelling of this data using both tomographic and raytrace modelling methods. These show a low velocity surface layer across the length of the profile with a clear graben-like structure beneath the centre of the Rift. This layer is likely to represent layered basalts and Mesozoic sediments beneath the plateau region and Quaternary sediments and volcanics within the Rift. An approximately 38 km thick crust, thinning slightly beneath the Rift and including at least 1 intra crustal reflector is also modelled.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8109 Continental tectonics--extensional (0905)
DE: 8180 Tomography
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting