Spectral inversion of S-wave spectra: implications for source characterization and seismic hazard simulation in Dahshour region, Northwestern Egypt

Abstract A Spectral Inversion Method (SIM), constrained by reference sites, is applied to separate path effects, site responses, and source spectra from observed S-waves using iterative least squares analysis. Results indicate that site responses inverted using the NBNS-reference site exhibit higher amplification than those using the NKOT-reference site at specific frequency ranges, with noticeable peaks in the 20 – 50 Hz range and moderate-frequency deamplification in some stations. Seismic wave attenuation is characterized by empirical relations, Q S = 259 f 0.76 (NBNS-reference site) and Q S = 261 f 0.77 (NKOT-reference site), highlighting frequency-dependent attenuation in the study area. The displacement source spectra decrease rapidly below 10 Hz for seismic events with 3.0 ≤ M L < 4.0. The obtained displacement source spectra exhibit a steeper high-frequency decay, deviating from the standard ω −2 source model. Derived source parameters include seismic moment (3.97E + 20 – 1.19E + 21 dyne cm), corner frequency (3.4 – 4.6 Hz), fault radius (163 – 221.9 m), and stress drop (1.7 – 10.1 MPa). To assess seismic hazards in the Dahshour region, stochastic simulations were performed for Earthquakes with M W ≥ 3.0 at the 6 October City site, which exhibited the highest amplification ( A O = 7.4). The highest simulated values for peak ground acceleration (PGA = 6.556 cm/s 2 ), peak ground velocity (PGV = 0.126 cm/s), peak ground displacement (PGD = 0.005 cm), and pseudo-spectral acceleration (PSA = 23.58 cm/s 2 ) correspond to the January 02, 2015, Earthquake at an epicentral distance of 28 km. These findings provide critical insights into seismic hazards in the Dahshour region, contributing to a better understanding of Earthquake risks in Northwestern Egypt.