Unraveling the unusual 22 November 2020 earthquake (Mw 3.5) in the Nile Delta Hinge Zone: Origin and tectonic implications

IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Journal of Seismology Pub Date : 2024-08-06 DOI:10.1007/s10950-024-10233-4
I.F Abu El Nader, Hany M. Hassan, Hazem Badreldin, Adel S. Othman, Ashraf Adly
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Abstract

On November 22, 2020, a moment magnitude of Mw 3.5 earthquake struck the highly populated Nile Delta. This event marked the first recorded earthquake in this area. We employed the polarity of P and S wave first motions, as well as SH and SV amplitudes and their respective ratios (SH/P and SV/SH), to constrain the focal mechanism solution. Furthermore, considering Brune's circular source model, kinematic source parameters were estimated through spectral analysis of available and reliable seismic data. The obtained solution reveals an oblique-slip fault mechanism, characterized by strike, dip, and rake angles of 341º, 69º, and -47º, respectively. Additionally, the two fault planes exhibit trends aligned with the E-W and NNW directions. This normal fault mechanism with a strike component aligns with previously identified events in various active areas of Egypt, indicating a dominant extensional stress regime. The trend/plunge of the P and T axes are determined to be 299º/46º and 42º/13º, respectively. Moreover, the NE trending of the T axis agrees well with the current extension stress field prevalent along the eastern border of Egypt. The average seismic moment and moment magnitude values for P and SH waves are estimated to be 1.86 × 1014 Nm, and 3.5, respectively. Furthermore, the average source values of radius and stress drop are calculated to be 304 m, and 29 bar, respectively. Through a comparative and comprehensive analysis of fault mechanism solutions in the Nile Delta region and its surroundings, we have concluded that the fault structures in the Hinge Zone and Cairo-Suez Shear Zone exhibit similarities. This finding provides evidence that the geodynamic processes and fault style are identical. In conclusion, the provided information contributes to our understanding of the seismotectonic characteristics and earthquake hazard in the epicentral region. Moreover, this study serves as a motivation for future site response and seismic hazard analyses based on a scenario-based approach.

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揭开尼罗河三角洲铰链区 2020 年 11 月 22 日不寻常地震(3.5 级)的神秘面纱:起源和构造影响
2020 年 11 月 22 日,人口稠密的尼罗河三角洲发生了 3.5 级地震。这次地震是该地区有记录以来的首次地震。我们利用 P 波和 S 波初动的极性,以及 SH 波和 SV 波的振幅及其各自的比率(SH/P 和 SV/SH)来约束焦点机制解决方案。此外,考虑到 Brune 的圆形震源模型,通过对现有的可靠地震数据进行频谱分析,估算了震源运动参数。得到的解决方案揭示了一个斜滑动断层机制,其特征是走向、倾角和倾斜角分别为 341º、69º 和 -47º。此外,两个断层面的走向与东西向和西北向一致。这种带有走向成分的正断层机制与之前在埃及多个活跃地区发现的事件相吻合,表明了一种主要的伸展应力机制。经测定,P 轴和 T 轴的走向/倾斜度分别为 299º/46º 和 42º/13º。此外,T 轴的东北走向与埃及东部边界目前普遍存在的延伸应力场十分吻合。据估计,P 波和 SH 波的平均地震力矩和力矩幅值分别为 1.86 × 1014 牛米和 3.5。此外,计算得出的半径和应力降的平均震源值分别为 304 米和 29 巴。通过对尼罗河三角洲地区及其周边地区的断层机制方案进行比较和综合分析,我们得出结论:铰链区和开罗-苏伊士剪切区的断层结构具有相似性。这一发现为地球动力过程和断层风格的相同提供了证据。总之,所提供的信息有助于我们了解震中地区的地震构造特征和地震危害。此外,本研究还为未来基于情景方法的场地响应和地震灾害分析提供了动力。
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来源期刊
Journal of Seismology
Journal of Seismology 地学-地球化学与地球物理
CiteScore
3.30
自引率
6.20%
发文量
67
审稿时长
3 months
期刊介绍: Journal of Seismology is an international journal specialising in all observational and theoretical aspects related to earthquake occurrence. Research topics may cover: seismotectonics, seismicity, historical seismicity, seismic source physics, strong ground motion studies, seismic hazard or risk, engineering seismology, physics of fault systems, triggered and induced seismicity, mining seismology, volcano seismology, earthquake prediction, structural investigations ranging from local to regional and global studies with a particular focus on passive experiments.
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