--> ABSTRACT: Shear Waves in an Anisotropic Earth, by Jack Cameron; #91030 (2010)

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Shear Waves in an Anisotropic Earth

Jack Cameron

Seismic shear waves propagate through an isotropic medium with a particle motion that is normal to the ray path. These seismic waves behave like light propagating through a crystal. Shear waves in an anisotropic earth exhibit the same features as light in an anisotropic crystal. The energy is split into two independent modes (birefringence), which are orthogonally polarized. There has been a great deal of optimism regarding the additional information that is available through the analysis of these waves. One potential application is detecting microfractures. The relationship between seismic measurements of polarized shear waves and microfractures is important.

If an abrupt change in anisotropy occurs, shear waves may split more than once, producing complex and ringy events. Data from the Silo field of southeastern Wyoming (courtesy of Colorado School of Mines) shows the occurrence of conflicting polarizations and multi-splitting of shear waves. Under these circumstances, interpretation of data is difficult and attempts to quantify fracturing may be misleading.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.