Crustal velocity structure across the Main Ethiopian Rift: results
from two-dimensional wide-angle seismic modelling
Geophysical Journal International, 162 (3):
994--106 (September 2005)DOI: 10.1111/j.1365-246X.2005.02710.x
Abstract
We present the results of velocity modelling of a recently acquired
wide-angle seismic reflection/refraction profile across the Main
Ethiopian Rift. The models show a continental type of crust with
significant asymmetry between the two sides of the rift. A 2- to
5-km-thick layer of sedimentary and volcanic sequences is modelled
across the entire region. This is underlain by a 40- to 45-km-thick
crust with a c. 15-km-thick high-velocity lowest crustal layer beneath
the western plateau. This layer is absent from the eastern side,
where the crust is 35 km thick beneath the sediments. We interpret
this layer as underplated material associated with the Oligocene
flood basalts of the region with possible subsequent addition by
recent magmatic events. Slight crustal thinning is observed beneath
the rift, where Pn velocities indicate the presence of hot mantle
rocks containing partial melt. Beneath the rift axis, the velocities
of the upper crustal layers are 5-10 per cent higher than outside
the rift, which we interpret as resulting from mafic intrusions that
can be associated with magmatic centres observed in the rift valley.
Variations in seismic reflectivity suggest the presence of layering
in the lower crust beneath the rift, possibly indicating the presence
of sills, as well as some layering in the proposed underplated body.