Attenuation of body waves in the crust beneath the vicinity of Cairo Metropolitan area (Egypt) using coda normalization method

Abstract

A digital waveform data set of 167 local earthquakes, recorded by the Egyptian Seismographic Network, was used to estimate the attenuation of body waves in the crust at the vicinity of Cairo Metropolitan area. The P-wave (Q−1α) and S-wave (Q−1β) attenuation were estimated by applying the coda normalization method to bandpass-filtered seismograms of frequencies ranging from 3 to 24 Hz. Q−1α values estimated at different frequency bands are ranged from 10.7 × 10−4 to 72.9 × 10−4, while the Q−1β values are ranged from 4.3 × 10−4 to 28.6 × 10−4. Estimates of Q−1α and Q−1β show a clear dependence on frequency. The frequency-dependent attenuation is found to be Q−1α = (19 ± 2) × 10−3f−0.8±.1 and Q−1β = (7 ± 1) × 10−3f−0.85±.1 for P and S waves, respectively. The ratio Q−1α/Q−1β is higher than unity in the entire analyzed frequency range. The obtained results are commonly observed in tectonically active regions characterized by high degree of heterogeneity.