<p>Northeastern Egypt and its adjoining seismic regions (Cairo-Suez district, Gulf of Suez, Triple Junction, Gulf of Aqaba) have historically experienced moderate-to-large earthquakes, highlighting the need for a detailed understanding of path attenuation and site response characteristics for effective seismic hazard assessment and mitigation. This study employs the generalized inversion technique (GIT) to estimate path attenuation and site parameters using earthquake recordings from multiple seismic stations in the region with magnitude larger than 3.0. In the first step of the inversion process, observed seismograms are decomposed into source, path, and site contributions, with a reference site constraint applied to ensure consistency in spectral decomposition and address the degrees of freedom issue and the trade-off between the decomposed factors. The attenuation models are developed as frequency-dependent functions, yielding the following S-wave quality factors: <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${Q}_{\text{S}}=162\pm 5.7 {f}^{0.86\pm 0.05}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Q</mi> <mtext>S</mtext> </msub> <mo>=</mo> <mn>162</mn> <mo>±</mo> <mn>5.7</mn> <msup> <mrow> <mi>f</mi> </mrow> <mrow> <mn>0.86</mn> <mo>±</mo> <mn>0.05</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>(NBST-reference site) and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">${Q}_{\text{S}}=166\pm 3.2 {f}^{0.84\pm 0.04}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Q</mi> <mtext>S</mtext> </msub> <mo>=</mo> <mn>166</mn> <mo>±</mo> <mn>3.2</mn> <msup> <mrow> <mi>f</mi> </mrow> <mrow> <mn>0.84</mn> <mo>±</mo> <mn>0.04</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>(TAMR-reference site). The frequency-dependent quality factor (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">${Q}_{\text{f}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Q</mi> <mtext>f</mtext> </msub> </math></EquationSource> </InlineEquation>) relationship indicates a low reference quality factor at 1 Hz (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">${Q}_{0}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Q</mi> <mn>0</mn> </msub> </math></EquationSource> </InlineEquation> < 200) and a strong frequency dependence (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">$n$</EquationSource> <EquationSource Format="MATHML"><math> <mi>n</mi> </math></EquationSource> </InlineEquation> > 0.8), characteristic of tectonically and seismically active regions. In the second step, site amplification characteristics at each recording station are quantified using site spectral amplitude ratios of horizontal to vertical components. Additionally, the predominant frequency at each recording station was calculated using the horizontal-to-vertical spectral ratio (HVSR) method. The predominant frequency values obtained from the HVSR method closely match those derived from the generalized inversion analysis at each station. The predominant frequencies obtained from these amplification curves allow for site classification, providing crucial insights into local site effects.</p>

Estimation of site effects and seismic Q factor using generalized inversion technique (GIT) in Northern Egypt

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发表日期：

2026年4月13日

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Hamada Saadalla,
Saleh Qaysi,
Abdalla Abdelnabi

摘要

Northeastern Egypt and its adjoining seismic regions (Cairo-Suez district, Gulf of Suez, Triple Junction, Gulf of Aqaba) have historically experienced moderate-to-large earthquakes, highlighting the need for a detailed understanding of path attenuation and site response characteristics for effective seismic hazard assessment and mitigation. This study employs the generalized inversion technique (GIT) to estimate path attenuation and site parameters using earthquake recordings from multiple seismic stations in the region with magnitude larger than 3.0. In the first step of the inversion process, observed seismograms are decomposed into source, path, and site contributions, with a reference site constraint applied to ensure consistency in spectral decomposition and address the degrees of freedom issue and the trade-off between the decomposed factors. The attenuation models are developed as frequency-dependent functions, yielding the following S-wave quality factors: ${Q}_{\text{S}}=162\pm 5.7 {f}^{0.86\pm 0.05}$ $Q_{S} = 162 \pm 5.7 f^{0.86 \pm 0.05}$ (NBST-reference site) and ${Q}_{\text{S}}=166\pm 3.2 {f}^{0.84\pm 0.04}$ $Q_{S} = 166 \pm 3.2 f^{0.84 \pm 0.04}$ (TAMR-reference site). The frequency-dependent quality factor ( ${Q}_{\text{f}}$ $Q_{f}$ ) relationship indicates a low reference quality factor at 1 Hz ( ${Q}_{0}$ $Q_{0}$ < 200) and a strong frequency dependence ( $n$ $n$ > 0.8), characteristic of tectonically and seismically active regions. In the second step, site amplification characteristics at each recording station are quantified using site spectral amplitude ratios of horizontal to vertical components. Additionally, the predominant frequency at each recording station was calculated using the horizontal-to-vertical spectral ratio (HVSR) method. The predominant frequency values obtained from the HVSR method closely match those derived from the generalized inversion analysis at each station. The predominant frequencies obtained from these amplification curves allow for site classification, providing crucial insights into local site effects.