Velocity Structure of the Upper Crust Across the Main Ethiopian Rift
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Date
2004-06
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Addis Ababa,University
Abstract
Refraction t~e is one of the geophysical investigation methods used 10 map the subsurface
layers based upon the velocity variation of the seismic wave as it propagates through different
geological materials.
As a part of the Ethiopia Afar Geoscientfic Lithospheric Experiment (EAGLE) project conducted
in January 200\ the detail study of the crustal seismic P-waves has been carried out to produce
the seismic model down to the depth of 10 la)1 ·from Chefodonsa (E5 13296, N99264 10 to Kula
(E575823, N886441) for about 120Km profile length across the Main Ethiopian Rift.
Five shot points with inter shot separation of about 46Km were used as seismic source and the
data were recorded on 120 geophones deployed in the study area at I km spacing.
The first arrival times were picked, processed and inverted using the generalized reciprocal
method (ORM); and gave the four major seismic layers up to the depth of 10 km across the rift.
There is a steady increase in P-wave veloc ity from about 3000mls in the first layer to about
6365m1s in the last layer. Lateral Velocity vari ations are also observed in the layers ..
Attempts have been made to correlate the seismic layers with the known geological fonnations.
Boarder faults and other major faults have been clearly identified.
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Keywords
Velocity Structure