Study of Surface Effects on LG Wave Propagation in Heterogeneous Crusts by a GS-BE Hybrid Method
Final rept. 1 Jan 1995-31 Dec 1997
CALIFORNIA UNIV SANTA CRUZ INST OF TECTONICS
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The objective of this research is to study the effects of surface topography, near-surface sedimentary structure and the associated small-scale heterogeneities on regional wave propagation, which is critical for both discrimination and yield estimation in monitoring the Comprehensive Test Ban Treaty and the Nuclear Non-Proliferation Treaty. This subject is also relevant to determining crustal structures and static corrections in exploration seismology. Our aim is to develop a hybrid method which couples the recently developed fast screen propagator theory and methods Wu, 1994 Wu and Xie, 1994 Wu and Huang, 1995 with Boundary Integral Equation BIE or Boundary Element BE methods to treat the influences of both volume heterogeneities and irregular interfaces, including the influence of surface topography. Chens Global Generalized ReflectionTransmission Matrix method is tested, as is the traditional boundary element method in the hybrid method. Connection formulations between the screen method and the BIE, BE methods have been developed and tested for the SH case. The excellent agreement between seismograms from direct propagation and from propagation using the connection formulas proves the correctness of the theory and the connection formulations. Numerical simulations of the influence of surface topography, sedimentary layers with rough bottoms, and small-scale random heterogeneities demonstrate the feasibility of the methodology. It is also shown that rough surface topography and an irregular sedimentary layer with scales close to the dominant wavelength can efficiently attenuate Lg waves.