Investigation of regional seismic wave attenuation and propagation in the Middle East
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This dissertation focuses on regional seismic attenuation studies in general but with some emphasis on the Middle East. I have several new approaches that have yielded insight into the behavior of regional seismic phase propagation. The research includes three main projects. Firstly, I developed a method combining the Two Station Method (TSM), Reverse Two Station Method (RTS), and Site Response (SS) measurements to tomographically map the attenuation quality factor Q and relative site responses for Lg and Sn waves. This method has allowed for the integration of three different observations into a single optimal model which is an important step forward in our ability to effectively measure high frequency wave attenuation as well as characterize site amplification. This method was then applied to the Caucasus. The results revealed significant lateral variations in seismic attenuation across the region, with high attenuation in Eastern Anatolia and significant lateral variations in the Lesser and Greater Caucasus regions. Notable impacts from sediments and shallow geology on regional seismic amplitudes were also observed. Secondly, the Double Two Station Method (DTSM) was employed to examine the effects of epicentral distance and source depth on Lg wave attenuation. This method is broadly applicable to regional wave propagation, but we tested this method in the northern Middle East. The findings demonstrated a positive correlation between epicentral distance and Qv measurements for certain regions, suggesting a significant influence of Sn-to-Lg conversion and possibly a deeper sampling by longer paths. The source depth of crustal events showed negligible impact on Lg attenuation. Lastly, a logistic regression model was used to produce the first quantitative Lg blockage map for the Middle East. The model identified widespread blockage in regions with oceanic crust and transition zones, such as the Mediterranean Sea and Caspian Sea. High blockage probabilities were also observed in eastern Anatolia, western Caucasus, and the Zagros fold belts. These works contribute to a better understanding of seismic wave propagation and attenuation in general and especially in the Middle East.
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Ph. D.