Accession Number : ADP204460

Title :   The Effects of Anisotropy on Regional Seismic Wave Propagation,

Corporate Author : YALE UNIV NEW HAVEN CT DEPT OF GEOLOGY AND GEOPHYSICS

Personal Author(s) : Park, Jeffrey ; Su, Liqiang ; Lilly, Jonathan

PDF Url : ADP204460

Report Date : 14 AUG 1995

Pagination or Media Count : 10

Abstract : We have examined the effect of seismic anisotropy on the scattering of surface waves in actively-deforming continental regions, many of which occur in areas of nonproliferation concern. We have approached the problem from three angles, (1) we have developed waveform inversion methods for Love-Rayleigh coupling in seismic data from the Tibetan Plateau and Tien Shan region, (2) we have developed a flat-layered surface wave code to study the effect of crust and upper-mantle anisotropy on crustal resonances, and (3) we have advanced wavelet-based signal processing methods to estimate the polarization of coherent seismic energy across a broadband seismic array. In data from the recent portable broadband PASSCAL deployment in Tibet, we found clear evidence of long-period Love-to-Rayleigh scattering that is best explained by lateral gradients of anisotropy in the upper mantle, developed in the course of the compression and uplift of the plateau. We developed a modal summation technique for waveform perturbations that allowed us to infer that both S and P wave anisotropy, with a ratio consistent with the mineral alignment of sheared peridotite, in the depth range 100-300 km are necessary to fit the observed data. Using a plane-layered geometry, we are investigating the effect of crust and upper mantle anisotropy on Love-Rayleigh coupling in the 5-30 second period range. Most previous studies have posited a horizontal or vertical axis of symmetry for seismic anisotropy, but our code can incorporate a tilted axis of symmetry, which enhances coupling and scattering effects. Such dipping geometries could develop in the crust as a result of thrust ramps in compressive tectonic regimes, either in the form of oriented crystals in shear zones or fine-layering of isotropic material.

Descriptors :   *SEISMIC DETECTION, *SEISMIC WAVES, *ARMS CONTROL, *NUCLEAR EXPLOSION DETECTION, *SEISMIC DISCRIMINATION, *EARTHQUAKES, SCATTERING, SYMPOSIA, SURFACE WAVES, MONITORING, ELASTIC PROPERTIES, FAULTS(GEOLOGY), SEISMIC DATA, WAVE PROPAGATION, ANISOTROPY, RESONANCE, EARTH CRUST, CALIFORNIA, TREATIES, PRIMARY WAVES(SEISMIC WAVES), RAYLEIGH WAVES, SEISMIC ARRAYS, EARTH MANTLE, TECTONICS, LOVE WAVES, LITHOSPHERE.

Subject Categories : Government and Political Science
      Seismology
      Seismic Detection and Detectors
      Nuclear Weapons
      Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE