Seismicity of Afar and the Main Ethiopian Rift From 2000 - 2002 G.C.
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Date
2011-06
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Addis Ababa University
Abstract
Earthquakes data recorded between 2000 and 2002 are used to study the seismicity of
Ethiopia mainly focused around Afar and the Main Ethiopian rift. The locations of 238
local earthquake are determined using P- and S- wave arrival times recorded on three
or more stations that resulted to a maximum of 1.5 root mean square (RMS). Previous
studies of seismicity by Brazier et al., 2006 has been revisited using the same data from
IRIS/PASSCAL broadband seismic experiments and adding more from ESSN (Ethiopian
Seismic Station Network) sources. Comparing the results in this study with Brazier et
al., 2006's, it is found that eight bogus events (earthquakes that didn't occur in the
real world) and six more teleseismic earthquakes are reported as if they occurred in the
Ethiopian neighborhood. On the other hand, it is observed that Brazier et al's work,
which is published in Bulletins of Seismological Society of America (BSSA), reported 25
earthquakes that are located with readings from seismic stations less than three which
puts doubt on the accuracy of the seismicity study. Another 53 new earthquakes are
identi ed in the database and located in this study which has improved details of the
seismicity of the region for the time period considered.
A Fortran program is written in 0.5 by 0.5 degree window and with 0.5 degree sliding
window in order to map the seismic energy release. The distribution of epicenter in this
study shows high seismic activity around 90N and 40:500E; 9:500N and 39:500E during the
study period, these epicenters are close to the N - S trending Ankober region, Kessem area
and Dofen volcano. Coda magnitudes are also estimated for the reported events. Similarly
b-values are estimated using both the least squares method and the maximum likelihood
method. b-value of 0.9 0.09 and 1.10 were obtained using the maximum-likelihood
method and using least square method determined respectively for the highly seismic
Ankober-Dofen region during the study period. On the other hand, seismic energy map
is developed for the whole region. The relatively high b-value estimated and the seismic
energy mapping showed that seismic energy are released in the form of small magnitude.
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Computational