The northern Red Sea in eastern Egypt is one of the world’s newest marine basins. The northern Red Sea is a very active seismic region and poses a significant hazard to the nearest cities on the Red Sea coast. On June 16, 2020, a moderate earthquake (M_L = 5.4), as published by the Egyptian National Seismic Network (ENSN), occurred in the northern Red Sea followed by several aftershocks, ranging in magnitude from 2.0 to 3.4. The best-fitting double-couple movement obtained using the full waveform moment tensor inversion of the main earthquake indicated strike-slip movement, with a minor normal component. The two nodal main shock planes were oriented NNE–SSW and ESE–WNW, respectively. The aftershocks sequences distribution did not coincide with the 16 Jun, 2020 main earthquake, neither in map view nor with respect to depth which may pointed to a secondary fault plane activation and stress triggered by the mainshock. The aftershocks clustered at the north western side of the main earthquakes and extend in the north western direction, which supported that the ESE–WNW plane is the fault plane. The spectral parameters of the S-wave displacement spectra of the main earthquake and its significant aftershock sequences were determined using the spectral inversion method and Brune’s $$\omega^{2}$$ω2 modulation. The obtained spectra are flat in the frequency range from 0.8 Hz to each corner frequency, and they decreased rapidly at frequencies of < 10 Hz. The calculated seismic moment, moment magnitude, corner frequency, source radius, and stress drop vary from 8.293E+18 to 7.541E+22 dyn·cm, 2.4 to 5.0, 2.2 to 8.2 Hz, 171 to 633 m, and 0.02 to 13 MPa, respectively. The moment magnitude is equal to or slightly higher than the local magnitude reported by ENSN. The calculated stress drops for the earthquakes increased with increasing earthquake size.

In order to distinguish between shallow earthquakes and quarrying activity, we evaluated 3069 seismic signals from 413 occurrences (112 explosions and 301 shallow earthquakes, depths 5 km), collected by the Aswan seismic sub-network in southern Egypt from 2010 to 2021. The spectral properties and related source parameters (e.g., seismic moment and corner frequency) using the estimated P-wave source spectra for both earthquakes and quarry blasts were investigated. The analysis showed that the P-wave source spectra of shallow earthquakes have higher corner frequencies (8.8–23 Hz) than quarry blasts (1.0–2.6 Hz) within the same magnitude range. The source spectra of quarry blasts exhibited significant misfits with the omega-square model and had steeper falloffs at high frequencies. The selected quarry blasts have a narrow seismic moment range, from 2.03 × 10¹¹to 1.35 × 10¹²Nm. Our results demonstrate that the evaluation of misfit of P-wave spectra from the omega-square source model, based on spectral amplitude characteristics of high- and low-frequency bands, is the most reliable discriminant method in the routine data analysis of the target area.

Aswan broadband seismic network with highly sensitive sensors and good station coverage gave the opportunity to study the seismicity distribution, focal depth, the fault plane solution, the attenuation of seismic wave, the station sites response, and the source spectra of Aswan earthquakes with magnitude ( M L ) \left({M}_{{\rm{L}}}) between 0.8 and 4.2 recorded from 2010 to 2023 comprehensively. Preliminary analysis of Aswan seismicity during the studied period indicated strike-slip mechanism with minor normal sense is dominant, relatively deep seismicity concentrated beneath Gabal Marawa, whereas shallow seismicity are dominant features of other zones in Aswan region, and the epicenter distribution characterized by cluster forms, frequently occurred earthquakes in the same patches, and concentrated in the intersection area between the two orthogonal fault systems. A generalized inversion technique (GIT) constrained by reference site is applied to separate the path effect, the recording station sites responses and the source spectra from the observed P- and S-waves by means of iterative least square analysis. The separated station sites effects show similar trend using P- and S-waves, with flat curve in the low frequency band from 0.8 to 8 Hz, whereas the station sites responses have peak amplitudes deviated from 4 to 10 in the higher frequencies. The attenuation through propagation is evaluated and empirically formulated Q p = ( 133 ± 2.09 ) f ( 0.54 ± 0.034 ) {{Q}}_{{\rm{p}}}\left=(133\left\pm 2.09){{f}}^{(0.54\left\pm 0.034)} and Q s = ( 91 ± 1.9 ) f ( 0.8 ± 0.045 ) {{Q}}_{{\rm{s}}}\left=(91\left\pm 1.9){{f}}^{(0.8\left\pm 0.045)} for P- and S-waves, respectively. The given attenuation fitting relation for P- and S-waves indicated the frequency dependence of seismic wave’s attenuation in the study area. The low-quality factor Q 0 {{Q}}_{0} at reference frequency ( f 0 {f}_{0} ) pointed that Aswan region is an active region. Furthermore, the low value of Q 0 {{Q}}_{0} would indicate that the medium is complex and highly heterogeneous. The third element separated from the observed seismogram is the displacement source spectra which modulated using Brune’s omega square. The advanced earthquake’s source parameters (seismic moment, corner frequency, moment magnitude, and static stress drop and source radius) and its scaling relations are computed using the converted windows of P- and S-waves. The displacement source spectra for seismic events with M L < 3 {M}_{{\rm{L}}}\lt 3 decayed rapidly at 20 Hz in the frequency bands of 0.8–50 Hz, whereas it is decreased rapidly at 10 Hz for seismic events with magnitude 3 ≤ M L < 4.2 3\le {M}_{{\rm{L}}}\lt 4.2 . The seismic moment, the source radius, and the corner frequency range from 9.50 × 10 ¹⁶ to 2.18 × 10 ²¹ dyne-cm, from 28 to 190 m, and from 4 to 36 HZ, respectively. The observed stress drops for the studied earthquakes vary from 0.01 to 12 Mpa, whereas the stress drop for S-portion ∆ σ S {\triangle \sigma }^{{\rm{S}}} ranged from 0.03 to 22 Mpa. The low stress drop values may reflect that reservoir–triggered earthquakes may have a lower stress drop than tectonic and crustal ones.

Well-recorded earthquakes located along the rift axis of the Red Sea, western Saudi Arabia, were investigated. These events are among the most significant recorded between 1997 and 2024 in this seismic zone. The moment tensor inversion, using full waveform data, was applied to determine the rifting mechanism and parameters of the investigated earthquakes. The optimum double-couple mechanism for investigated earthquakes revealed normal faulting with minor strike slip movement along the red sea spreading axis. The most recent earthquakes were felt in nearby cities, prompting a study to understand the fault mechanisms and assess the impact of strong ground motion parameters on western Saudi Arabian cities, which have rapidly developed along the Red Sea’s active rifting system. The stochastic simulation method, based on the site spectral model, was used to estimate the effects and strong ground motion parameters of the most recent and significant earthquakes in the western cities of Saudi Arabia: one on June 16, 2020 ( M L {M}_{{\rm{L}}} = 5.5), and another on April 14, 2023 ( M L {M}_{{\rm{L}}} = 4.5). The results suggest that Al-Muwaileh and Duba cities experienced peak ground accelerations of 9.113 and 8.673 cm/s ² from the June 16, 2020, earthquake and 2.347 and 1.707 cm/s² from the April 14, 2023, earthquake, respectively. The pseudo-seismic spectral acceleration values were 2.282 × 10 ¹ and 2.379 × 10 ¹ cm/s ² in Duba and Al-Muwaileh, respectively, for the June 16, 2020, earthquake and 4.837 and 6.752 cm/s ² for the April 14, 2023, earthquake.