Source parameters of some recent earthquakes in the Gulf of Aqaba, Egyptمعاملات المصدر لبعض الزلازل الحديثه بخليج العقبه – مصر

Gulf of Aqaba is recognized as an active seismic zone where many destructive earthquakes have occurred. The estimation of source parameters and coda Q attenuation are the main target of this work. Fifty digital seismic events in eight short-period seismic stations with magnitude 2.5–5.2 are used. Most of these events occurred at hypocentral depths in the range of 7–20 km, indicating that the activity was restricted in the upper crust. Seismic moment, Mo, source radius, r, and stress drop, Δσ, are estimated from P- and S-wave spectra using the Brune’s seismic source model. The average seismic moment generated by the whole sequence of events was estimated to be 4.6E + 22 dyne/cm. The earthquakes with higher stress drop occur at 10-km depth. The scaling relation between the seismic moment and the stress drop indicates a tendency of increasing seismic moment with stress drop. The seismic moment increases with increasing the source radius. Coda waves are sensitive to changes in the subsurface due to the wide scattering effects generating these waves. Single scattering model of local earthquakes is used to the coda Q calculation. The coda with lapse times 10, 20, and 30 s at six central frequencies 1.5, 3, 6, 12, 18, 24 Hz are calculated. The Qc values are frequency dependent in the range 1–25 Hz, and are approximated by a least squares fit to the power law [\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {Q_c}(f) = {Q_o}{(f/{f_o})^\eta } $$\end{document}]. The average of Qc values increases from 53 ± 10 at 1.5 Hz to 700 ± 120 at 24 Hz. The average of Qo values ranges from 13 ± 1 at 1.5 Hz to 39 ± 4 at 24 Hz. The frequency exponent parameter η ranges between 1.3 ± 0.008 and 0.9 ± 0.001.