Spatial variation of coda wave attenuation using aftershocks of the Al Hoceima earthquake of 24 February, 2004, Morocco

Abstract

On 24th February 2004 a significant earthquake (M d = 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 Seconds) in order to sample the earth's crust only. The values of Q c esti-mated for all the three stations show a strong frequency dependent relationship of the form Q c = Q 0 f n , where Q 0 is Q c 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 Q 0 suggest that Al Hoceima area is highly heterogeneous and the n parameter in-dicates a meaning frequency dependence of Q c .