The present study presents the analysis of a moderate earthquake (Mw 4.0) and its largest aftershocks located along the Red Sea coast, southwestern Saudi Arabia, with the aim to understand the enigma of peculiar seismicity in the Arabian Shield. We analyzed a high-quality waveform dataset collected from ten well-recorded earthquakes of moment magnitude ranging from 2.0 to 4.0 in order to determine the hypocenter locations and focal mechanisms. The focal mechanisms were retrieved from the regional moment-tensor inversion for the mainshock and using the P-wave polarities for the corresponding aftershocks of Mw ≥ 2.0, respectively. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. The combination of the nearby fault trends and the obtained results from hypocentral relocations, focal mechanism solutions, and stress tensor inversion emphasizes that the NE fault trend is likely to be the causative fault resulting in the 2017 Namas earthquake sequence, implying that the local tectonic setting is incompatible with the large-scale regional tectonics of the Red Sea opening. On the contrary, estimates of low-stress drops exhibit typical values compatible with those reported for the shallow plate-boundary earthquakes that occurred in the Red Sea, suggesting that the existing weak zones in the southernmost part of the Arabian Shield may be attributed to the large-scale regional tectonics of the Red Sea opening.

中文翻译：

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对沙特阿拉伯红海东翼中度地震的分析

本研究对位于沙特阿拉伯西南部红海沿岸的中等地震 (Mw 4.0) 及其最大余震进行了分析，旨在了解阿拉伯地盾中特殊地震活动的谜团。我们分析了从十次记录良好的地震中收集的高质量波形数据集，其矩震级范围为 2.0 到 4.0，以确定震源位置和震源机制。震源机制分别从主震的区域矩张量反演和 Mw ≥ 2.0 的相应余震的 P 波极性中得到。使用应力张量反演反演震源机制解以反演地震应力。结合附近断层趋势和震源重定位获得的结果，震源机制解，应力张量反演强调 NE 断层趋势很可能是导致 2017 年 Namas 地震序列的成因断层，这意味着局部构造背景与红海开放的大规模区域构造不相容。相反，低应力降的估计值与红海浅层板块边界地震报告的值一致，这表明阿拉伯地盾最南端的现有弱区可能归因于红海开放的大规模区域构造。这意味着当地的构造环境与红海开放的大规模区域构造不相容。相反，低应力降的估计值与红海浅层板块边界地震报告的值一致，这表明阿拉伯地盾最南端的现有弱区可能归因于红海开放的大规模区域构造。这意味着当地的构造环境与红海开放的大规模区域构造不相容。相反，低应力降的估计值与红海浅层板块边界地震报告的值一致，这表明阿拉伯地盾最南端的现有弱区可能归因于红海开放的大规模区域构造。