Velocity Structure of the Uppermost Crust Along the Main Ethiopian Rift
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Date
2005-06
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Addis Ababa Universty
Abstract
Ethiopia is located at a plate tectonic triple-rift junction (Mohr 1980) where the East
African Rift System meets the Gulf of Aden and Red Sea with spreading axes at Afar.
A seismic study over the area has obvious implications on our knowledge concerning the
structure and evolution of the Earth. This study focuses on the determination of the
velocity structure of the uppermost crust along the Main Ethiopian Rift, which runs from
Awassa to Nazreth to a depth of 10km on a 104km seismic profile.
Seismic waves generated by explosive charges detonated in boreholes are used to study
the area. The seismograph Texans deployed on the surface are used to record the seismic
energy refracted back to the surface from geological interfaces.
The time of first arrivals of these refracted waves were picked, processed and inverted using the
General Reciprocal Method (GRM).
Basically three refractors at an average depth of, 2000m, 4500m, and 7000m were
identified with their corresponding average P wave velocities of 3950m/s, 5726m/s and
6320m/s. The geologic sections of the area are shown in Fig (6.11).
Attempts have been made to correlate the seismic layers with the various stratigraphic
units.
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Ethiopia