Estimation of Coda Wave Attenuation in Northern Morocco

Abstract

We studied the attenuation of coda waves and its frequency and lapse-time dependence in northern Morocco. We analysed coda waves of 66 earthquakes recorded in this region during 2008 for four lapse time windows of length 30, 40, 50, and 60 s, and at five frequency bands with central frequency in the range of 0.75–12 Hz. We determined the frequency dependent Q c relation for the horizontal (NS and EW) and vertical (Z) component seismograms. We analyzed three-component broadband seismograms of 66 local earthquakes for determining coda-Q based on the single back-scattering model. The Q c values show strong frequency dependence in 1.5–12 Hz that is related to high degree of heterogeneity of the medium. The lapse time dependence of Q c shows that Q 0 (Q c at 1 Hz) significantly increases with lapse time that is related to the depth dependence of attenuation and hence of the level of heterogeneity of the medium. The average frequency-dependent Q c(f) values are $$Q_{\text{c}} = (143.75 \pm 1.09)f^{(0.864 \pm 0.006)},$$ $$Q_{\text{c}} = (149.12 \pm 1.08)f^{(0.85 \pm 0.005)}$$ and $$Q_{\text{c}} = (140.42 \pm 1.81)f^{(0.902 \pm 0.004)}$$ for the vertical, north–south and east–west components of motion, respectively. The frequency-dependent Q c(f) relations are useful for evaluating source parameters (Singh et al. 2001), which are the key inputs for seismic hazard assessment of the region.