Propagation of regional seismic phases (Sn and Lg) in the Middle East and East Asia
Abstract
I have studied the propagation of the regional seismic waves (Sn and Lg) in the Middle East (ME) and East Asia. The methods used in this study are : (1) the reverse two-station method (RTM) to determine the attenuation and site response, (2) the logistic regression/Bayesian lasso method to predict the probability of observing Sn and (3) the LSQR method to generate attenuation and predicted probability tomography. I have constructed new frequency-dependent Lg and Sn attenuation models in China. The results show high Lg Qs in SE and NE China and the Tarim basin, while low Lg Qs are found in the Tibetan plateau. High Sn Qs are found in the Sichuan basin and the Ordos and Tibetan plateaus. Low Sn Qs are found in eastern China and northern, eastern Tibetan plateau. I have also estimated the site response with both Lg and Sn in China. With the differential site response results, I found that the effective Sn attenuation may include the effect of the crustal legs, which is supposed to be eliminated in RTM. I have also constructed a model that shows the spatial variability in Sn propagation in the ME and East Asia. The model has successfully predicted the probability of observing Sn as well as being blocked. We observe high probabilities of observing Sn in stable and oceanic regions, such as the Arabian Plate, the Mediterranean Sea. In tectonically active areas, such as the Tibetan and Iranian plateaus, I have observed a low probability of observing Sn propagation. These models should help determine where existing attenuation models are significantly biased by systematic data censorship.
Degree
Ph. D.