Seismic attenuation of regional phases in the northern Middle East and the Tibetan Plateau

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] I study the regional seismic phase attenuation to (1) infer rheology and temperature of the crust and uppermost mantle and to (2) develop reliable and transportable nuclear discriminants. The methods used in my research have advantages over other methods by eliminating the influence of earthquake source, instrument response, and site responses. I have measured regional phase Q values for two continental-continental collision zones, the northern Middle East and the Tibetan Plateau. The regional phase Q is typically assumed as the intrinsic Q, whose lateral variation suggests temperature structure of the crust and the uppermost mantle. In the northern Middle East, large varations in regional phase Q models are observed, such as low Q within the Anatolian Plateau and high Q within much of the Arabian Plate. In Tibet, I have observed low Q in the northernmost Tibetan Plateau and high Q in the Qaidam basin. My method to solve site responses can be applied in earthquake hazard studies. Azimuthal anisotropy of Q has been observed, which is probably related to focusing/defocusing or crustal anisotropy. Intrinsic attenuation could be isolated by solving the inverse problems involving the effects of azimuthal anisotropy and small-scale scattering. Such intrinsic attenuation calculated from regional seismic phase has been used to estimate crustal temperature of the Tibetan Plateau.