Source parameters and stress drop variability in northeastern Egypt and their implications for seismic hazard assessment

Northeastern Egypt and its surrounding seismogenic provinces, including the Cairo–Suez district, the Gulf of Suez, the Gulf of Aqaba, and the Northern Red Sea, have experienced recurrent moderate-to-strong earthquakes. These events underscore the importance of robust constraints on earthquake source characteristics for reliable seismic hazard assessment. In this study, we apply the Generalized Inversion Technique (GIT) to broadband seismic recordings to simultaneously resolve source, path, and site effects for earthquakes with local magnitudes ranging from 3.0 to 6.1. Using a carefully selected reference site, the observed S-wave spectra are decomposed into their fundamental components, minimizing trade-offs between source and site terms. After correcting attenuation and site response, average S-wave displacement source spectra were obtained and interpreted using the classical circular crack model. Key spectral parameters, including the long-period spectral level and corner frequency, were estimated and used to derive seismic moment, moment magnitude, source radius, and stress drop. The analyzed spectra exhibit a pronounced high-frequency decay below 10 Hz within the investigated frequency band (0.8–50 Hz). Estimated corner frequencies range from 2.1 to 5.4 Hz, seismic moments from 7.4 × 10¹² to 1.04 × 10¹⁷ NM, moment magnitudes from 2.5 to 5.3, source radii from about 240 to 670 m, and stress drops from 0.2 to 93.8 MPa. The resulting scaling relationships are largely consistent with self-similar rupture behavior. The derived source parameters provide new, statistically robust constraints on earthquake rupture processes in northeastern Egypt. These results improve our understanding of regional seismotectonic and provide essential input for seismic hazard analysis and ground-motion modeling in densely populated and strategically important areas.