Frequency dependent attenuation and relative site response of western Tibet

<p>We have formulated frequency dependent Lg and Pg attenuation tomographic models to investigate the<br />crustal Q values and its tectonic implications beneath western Tibet. The frequency dependent<br />behaviour of both Lg and Pg are studied for the frequency bands of 0.2-0.6, 0.6-1.0 and 1.0-1.4 Hz at<br />central frequencies of 0.4, 0.8, and 1.2 Hz, respectively, implementing both Two-Station Method<br />(TSM) and Reverse Two-Station Method (RTSM). The amplitudes of both the waves are fundamentally<br />sensitive to the crustal structures and are controlled by both scattering and intrinsic attenuation. The<br />frequency dependent characteristics of Q_Lg and Q_Pg are consistent in nature for the region. Moderate to<br />high Q values evident in the Lhasa terrane could supplement the trace of underthrusting Indian<br />lithosphere beneath the region. The average Q values for both Lg and Pg increase with increasing<br />frequency. The frequency dependent parameter &#951; shows quite high values, for both the waves using<br />TSM and RTSM, which may indicate strong heterogeneities present in the crust. Subsequently, relative<br />site responses at each station are studied using RTSM for the central frequencies of 0.4, 0.8, and 1.2<br />Hz. Weak to negative site responses are mostly dominant in western Tibet. Relative site responses are<br />found to vary with frequency which could be associated with the sampling depth. We found no<br />correlation of site responses with the elevation.</p>