Accession Number : ADP204438

Title :   Regional Wave Propagation in and around the Tibetan Plateau,

Corporate Author : SOUTH CAROLINA UNIV COLUMBIA

Personal Author(s) : Owens, T. J. ; Crotwell, H. P. ; McNamara, D. E. ; Randall, G. E.

PDF Url : ADP204438

Report Date : 14 AUG 1995

Pagination or Media Count : 10

Abstract : The Tibetan Plateau is a dominant structural feature influencing seismic wave propagation in Central Asia. Using data from the 1991-92 Tibetan Plateau Seismic Experiment deployment of broadband PASSCAL sensors, we are studying the effects of the Tibetan Plateau on a variety of regional phases propagating within the plateau and crossing its boundaries. In this report, we summarize results from two such studies. First, the propagation and attenuation characteristics of Lg are used to document that Lg can propagate within the thickened crust of the Tibetan Plateau and to confirm previous studies showing that all boundaries of the plateau are effective barriers to Lg propagation. Our results further indicate that attenuation of Lg within the plateau is relatively high, comparable to areas of active tectonics, such as the Basin and Range Province. The second study involves waveform modeling of Pn and Sn waveforms from regional events of moderate magnitude. Source mechanisms for these events have been recently published, providing the necessary constraints to begin detailed structural modeling. It has been known for a decade that there are significant lateral variations in Sn propagation within the plateau, specifically that the central northern Tibetan Plateau blocks the propagation of high-frequency Sn phases. Using broadband regional seismograms from events within the plateau, we document that this blockage is strongly frequency-dependent. The available station spacing allows us to observe a rapid loss of high frequencies as regional S phases cross into the northern plateau while frequencies below 0.05Hz propagate throughout the plateau. Variations in the displacement pulse-shapes through the transition into the northern plateau are more easily explained by a changes in Poisson's ratio with depth than by simply rapid changes in the attenuation structure.

Descriptors :   *SEISMIC DETECTION, *SEISMIC WAVES, *ARMS CONTROL, *NUCLEAR EXPLOSION DETECTION, SYMPOSIA, SURFACE WAVES, UNDERGROUND EXPLOSIONS, NUCLEAR EXPLOSION TESTING, SEISMIC DATA, WAVE PROPAGATION, SEISMIC DISCRIMINATION, TREATIES, ASIA, PRIMARY WAVES(SEISMIC WAVES), POISSON RATIO, TECTONICS.

Subject Categories : Seismology
      Seismic Detection and Detectors
      Nuclear Weapons
      Government and Political Science

Distribution Statement : APPROVED FOR PUBLIC RELEASE