Velocity Structure Of The Uppermost Crust Along The Main Ethiopian Rift

Ethiopia is located at a plate tectonic triple-rift junction (Mohr 1980) where the EastrnAfrican Rift System meets the Gulf of Aden and Red Sea with spreading axes at Afar.rnA seismic study over the area has obvious implications on our knowledge concerning thernstructure and evolution of the Earth. This study focuses on the determination of thernvelocity structure of the uppermost crust along the Main Ethiopian Rift, which runs fromrnAwassa to Nazreth to a depth of 10km on a 104km seismic profile.rnSeismic waves generated by explosive charges detonated in boreholes are used to studyrnthe area. The seismograph Texans deployed on the surface are used to record the seismicrnenergy refracted back to the surface from geological interfaces.rnThe time of first arrivals of these refracted waves were picked, processed and inverted using thernGeneral Reciprocal Method (GRM).rnBasically three refractors at an average depth of, 2000m, 4500m, and 7000m werernidentified with their corresponding average P wave velocities of 3950m/s, 5726m/s andrn6320m/s. The geologic sections of the area are shown in Fig (6.11).rnAttempts have been made to correlate the seismic layers with the various stratigraphicrnunits.

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