Attenuation of Seismic Coda-Waves in Algeria: Algiers Vicinity and Mitidja Basin

A single backscattering method is used to estimate coda quality factor functions (Q(c)) from coda-wave attenuation for the Algiers vicinity and eastern part of the Mitidja Basin. The frequency-dependent Q(c) relation is determined using a high-quality data set with good signal-to-noise ratios (SNR > 5) of 228 accelerogram waveforms of local earthquakes in the magnitude range 2.3-5.3, with focal depth varying from 1.3 to 31 km and epicentral distances less than 65 km. We studied the frequency and lapse time dependence of coda-wave attenuation through the variation of coda window length of 20, 30 and 35 s for seven frequency bands in the range of 1.5-24 Hz. The obtained average Q(c) increases with increasing coda window length, implying an increase in sampled depth. The Q(c) of horizontal components (N and E) are slightly lower than the Q(c) of the vertical component (Z). The obtained low values of Q(c) and high values of frequency-dependent parameter n indicate that the penetration depth that consists of the crust and part of the upper mantle beneath the Algiers region is seismically active with a high level of heterogeneity. The average frequency-dependent Q(c) values in the three directions are Q(c)Z = (69.76 +/- 2.98)f((0.82 +/- 0.01)), Q(c)N = (60.2 +/- 4.86)f((0.88 +/- 0.03)) and Q(c)E = (59.63 +/- 5.07)f((0.88 +/- 0.03)) with a coda window length of 20 s in which the penetration depth is 56.2 km and the covered area is 8141 km(2).