Vol.5, No.8A1, 72-77 (2013) Natural Science
http://dx.doi.org/10.4236/ns.2013.58A1009
Spatial variation of coda wave attenuation using
aftershocks of the Al Hoceima earthquake of 24
February, 2004, Morocco
Abderrahim Boulanouar1*, Lahcen El Moudnib1,2, Mimoun Harnafi2, Taj-Eddine Cherkaoui2,
Abdelaali Rahmouni1, Mohamed Boukalouch1, Jamal Sebbani1
1Physics Department, Faculty of Science, Mohammed V University-Agdal, Rabat, Morocco;
*Corresponding Author: aboulanouar1@gmail.com
2Earth Science Department, Scientific Institute, Mohammed V University-Agdal, Rabat, Morocco
Received 6 July 2013; revised 6 August 2013; accepted 13 August 2013
Copyright © 2013 Abderrahim Boulanouar et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
On 24th February 2004 a significant earthquake
(Md = 6.4) occurred in the north of Morocco
causing great damage in the vicinity of Al Ho-
ceima region. This area is characterized by a
complex faulting system as a result of com-
pressional tectonic forces. Three short period
seismic stations are set in this area of interest
and recordings from these stations were used in
this study. In order to complete our knowledge
of attenuation, 60 local earthquakes are re-
corded a few days after the great earthquake
with magnitude Ml 2.6 - 5.0 to estimate seismic
attenuation. For this purpose, we applied the
single backscattering model of Aki & Chouet
1975 in the frequency range for 1 to 8 Hz. The
study of coda waves was limited to a relatively
short lapse time (20 Seco nds) in order to sample
the earth’s crust only. The values of Qc esti-
mated for all the three stations show a strong
frequency dependent relationship of the form Qc
= Q0fn, where Q0 is Qc at 1 Hz , and n represents
the degree of frequency dependence, and re-
flects the level of crustal heterogeneities to
varying degrees. The average frequency de-
pendent attenuation relationship has been ob-
tained which indicates that the attenuation is
high in this region. Finally to conclude our work,
the values of Q0 suggest that Al Hoceima area is
highly heterogeneous and the n parameter in-
dicates a meaning frequency dependence of Qc.
Keywords: Attenuation; Coda Waves; Single
Backscattering Model; Al Hoceima; Morocco;
Seismic; Earthquak e
1. INTRODUCTION
Al Hoceima is located among the most active seismic
zones in Morocco between the African and Eurasian
plates [1]. During the last 10 years, Al Hoceima has been
affected by two strong earthquakes [1,2], the first on
May 26th, 1994 (Mw = 6.0) and the later on February
24th, 2004 (Mw = 6.4). That’s why, the study of its seis-
micity is very important in order to establish the seismic
hazard assessment for this important area. Although this
is a very active seismic zone, little is known about the
seismic attenuation.
Attenuation, inverse of quality factor, is one of the
most fundamental proprieties of seismic waves from
which a lot of information about the earth can be de-
duced [3]. This parameter is an important factor for un-
derstanding the physical mechanism of seismic wave
attenuation in relation to the composition and physical
condition of the Earth’s interior and it is also an essen-
tial parameter for the quantitative prediction of strong
ground motion for the viewpoint of engineering seis-
mology [4]. This is also important for seismic hazard
measurement [4].
The attenuation can be described as the decay of the
seismic waves’ amplitude [5]. The single backscattering
model given by Aki and Chouet [5], has been used in this
study. This method is widely applied to studies in the
crustal structures in different parts in the world [3,6-11].
In the present study, the seismic attenuation was inves-
tigated in Al Hoceima region by analyzing a large num-
ber of short period local seismograms and comparing it
with other regions of the world [8]. The results of this
study are discussed and compared with previous results
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