A Coupled Local Mode Investigation of Elastic Anisotropy in Shallow Water Environments: A Study of Antisotropy Beyond VTI
Final rept., 1 Jan 2003-31 Mar 2005
WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
Pagination or Media Count:
This paper presents theoretical and numerical results for the coupled mode, shallow water seismo-acoustic wavefield in generally anisotropic, range-dependent media. General anisotropy affects the form of the elastic stiffness tensor, which directly affects the polarization of the local modes, the frequency and angular dispersion curves, and the coupling of the local modes in range-dependent media. The effects of anisotropy 1-D models and the combination of anisotropy and lateral heterogeneity 2-D models are examined. Perhaps surprisingly, horizontally polarized particle motion cannot be ignored when sediment anisotropy is present. Depending on the propagation direction relative to the symmetry axis orientation, even weak anisotropy may have a significant impact on seismo-acoustic wave propagation, exhibiting particle motion polarization in all three coordinate directions. Transversely isotropic TI media with a non-vertical symmetry axis allow both quasi-P-SV and quasi-SH modes to carry energy. The discrete modes for an anisotropic medium are best described as generalized P-SV-SH modes with polarizations in all three Cartesian coordinate directions. The superposition of these generalized P-SV-SH modes describe the seismo-acoustic signal and illustrate the importance of using an elastic treatment of the seafloor bottomsub-bottom for low frequency shallow water seismo-acoustic wave propagation.
- Physical and Dynamic Oceanography