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1 Department of Applied Physics
University of Almería
Almería, Spain
2 Andalusian Institute of Geophysics
and Seismic Disasters Prevention
University of
Almería
Almería, Spain
ajlloret{at}ual.es
A method to determine the spectral parameters, spectral level
0, corner frequency f0, and attenuation
factor Q, using a genetic algorithm (GA), is presented. An
adequate strategy for the GA was chosen by means of the 2D Ackley
function. For modeling the seismic spectrum, a Boatwright source model and an
attenuation factor independent of the frequency were used. Several objective
functions are tested, and the best was found to be the L2 norm of the log
difference between the observed and modeled spectra. To check the accuracy of
the method, some tests with synthetic spectra were made, including spectra with
noise. Real data, which have been already studied with other spectral methods,
were analyzed to compare the results. The spectral parameters of 13 earthquakes
(Granada, southern Spain) were calculated, as well as its source parameters: the
seismic moment M0, the source radius r, and the
stress drop 
, following Brunes model. The seismic
moments ranged from 3.65E + 17 to 9.98E + 18 dyne cm; the radii were
between 0.08 and 0.2 km, and the static stress drops ranged from 0.32 to 1.73
bars. The attenuation factors ranged from 53 to 726, with an averaged value of
303. The results obtained are similar to those obtained by other researchers
working with events of comparable magnitudes in the region.
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