Study of Surface Effects on LG Wave Propagation in Heterogeneous Crusts by a GS-BE Hybrid Method

摘要

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. Chen's Global Generalized Reflection/Transmission 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.