Retrieving detailed subsurface velocity structures down to the seismic bedrock at any given site is a crucial step to delineate the site amplification factors accurately and precisely. The present research work contributes first new estimations for detailed velocity structures down to the seismic bedrock beneath the Egyptian National Seismological Network (ENSN) stations, which are distributed in Egypt nationwide. We used the diffuse field assumption for earthquakes to reproduce the horizontal to vertical spectral ratios (EHVSR) at these stations. We accepted waveform database of 424 earthquakes recorded at 75 ENSN stations. After achieving the inverted subsurface velocity structures, we establish site-specific frequency-depth regression and map the V and seismic bedrock depth beneath Egypt. Because of comparability regarding the seismic site class of B and C, the regression coefficients of the newly established frequency-depth regression exhibit similarity with those achieved from previous regressions in Japan. Furthermore, we observe modest consistency between the seismic bedrock depths and the various geologic features, particularly agreement between basin-shape seismic bedrock depths and the existence of Cretaceous and Jurassic extensional basins. Our findings suggest that the Precambrian basement rocks can be interpreted as the seismic bedrock in Egypt. One of the most significant obstacles in the present work is the low-dense distribution of ENSN stations nationwide. However, the achieved results raise new questions and challenges regarding precise and accurate future estimations for site amplification calculations at different localities in Egypt, particularly for urban planning by engineers.

中文翻译：

---

通过地震扩散场假设反演埃及地震台网的地下速度结构


在任何给定地点检索详细的地下速度结构直至地震基岩是准确和精确地描述地点放大系数的关键步骤。目前的研究工作首次对埃及国家地震网络（ENSN）台站下方的地震基岩的详细速度结构进行了新的估计，这些台站分布在埃及全国范围内。我们使用地震的扩散场假设来重现这些台站的水平与垂直谱比 (EHVSR)。我们接受了 75 个 ENSN 台站记录的 424 次地震的波形数据库。在实现反演的地下速度结构后，我们建立了特定地点的频率深度回归并绘制了埃及下方的 V 和地震基岩深度。由于B级和C级地震站点的可比性，新建立的频率-深度回归的回归系数与日本以前的回归所得到的回归系数表现出相似性。此外，我们观察到地震基岩深度与各种地质特征之间有一定的一致性，特别是盆地形状的地震基岩深度与白垩纪和侏罗纪伸展盆地的存在之间的一致性。我们的研究结果表明，前寒武纪基底岩石可以解释为埃及的地震基岩。目前工作中最重要的障碍之一是全国范围内 ENSN 站的低密度分布。然而，所取得的结果提出了新的问题和挑战，涉及埃及不同地点场地放大计算的精确和准确的未来估计，特别是工程师的城市规划。