An Inversion Model of Receiver Function for Moho Depth Determination Beneath Locations of the Ethiopian Seismic Network Stations and their Surroundings
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Date
2016-06
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Addis Ababa Universty
Abstract
Moho depths or crustal thicknesses at four stations of the Ethiopian Seismic Station
Network (ESSN) are estimated from Receiver Functions studies. We used
high quality seismic data recorded at ANKE (Ankober), DILA (Dila), HARE (Harar)
and SEME (Semera) stations for earthquakes located at epicentral distances ranging
from 30o to 100o and magnitude M 5:5. We applied frequency domain
deconvolution technique to remove all effects from the earthquakes source and
propagation path to make the RFs dependent only on the structure beneath the
seismic stations. A linearized-iterative inversion is applied on the generated radial
component of the Receiver functions. From the four stations in the study,
the minimum number of teleseismic earthquakes is 14 for Harar while the maximum
is 39 for Ankober. The estimated values for the Moho depth are 42 1:7km,
36 2km, 38 2kmand 26 2kmfor Ankober, Dila, Harar and Semera respectively.
We have achieved a reasonably good fit between the observed and synthetic RFs
which demonstrates the goodness of the inversion. The lowest Moho depth is observed
for Semera station which implies a thinned crust while the highest crustal
thickness is achieved for Ankober that lies along the western plateau margin. The
second low Moho depth is calculated for Dila station while the one for Harar is an
intermediate one. Our results agree with previous observations which strengthens
the fact that Moho depths estimated for stations that lie within the rift and
rift margins are lower than those located in the plateaus. On the other hand, our
RFs inversions show low velocity gradient at about 15km depth at Semera stations
while high velocity gradient is noticed at Ankober station. This may imply
a cooled magma from previous dike or sill intrusions beneath Ankober station
while the observation at Semera indicates the existence of melt at that depth
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Keywords
Moho Depth Determination