The Effects of Anisotropy on Regional Seismic Wave Propagation,

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.

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Document Details

Document Type
Technical Report
Publication Date
Aug 14, 1995
Accession Number
ADP204460

Entities

People

  • Jeffrey Park
  • Jonathan Lilly
  • Liqiang Su

Organizations

  • Yale University

Tags

Communities of Interest

  • Air Platforms
  • Sensors

DTIC Thesaurus Topics

  • Doppler Effect
  • Earth Models
  • Forward Scattering
  • Frequency
  • Geology
  • Geometry
  • Geophysics
  • Group Velocity
  • Love Waves
  • Phase Velocity
  • Plane Waves
  • Rayleigh Waves
  • Scattering
  • Seismic Waves
  • Surface Waves
  • Wave Propagation
  • Waveforms

Readers

  • Electromagnetic Wave Scattering and Antenna Radiation Engineering
  • Materials Science and Engineering.
  • Seismology

Technology Areas

  • AI & ML
  • AI & ML - Bayesian Inference