Seismic wave propagation in anisotropic rocks with applications to defining fractures in earth crust

Yong-Gang Li

Published February 1, 2016, SCEC Contribution #8135

Abundant evidence of rock anisotropy has been observed in most earth materials,
at least in the upper crust, using three-component seismometers in microearthquake
networks, borehole vertical seismic profiling (VSP), and reflection
seismic exploration. A fundamental observation of seismic anisotropy is shearwave
splitting, in which shear waves polarized in one direction travel faster than
orthogonally polarized shear waves in the anisotropic medium. With the increasing
resolution of seismometer in recent decades, wave polarization anomalies and
directional velocity variations of three distinct body waves referred to as qP, qSV
and qSH have been recorded in anisotropic media. Two shear waves also show
the difference in attenuation when they travel in the anisotropic medium. These
observations of seismic wave propagation anisotropy are becoming increasingly
useful in stratigraphic and lithological interpretations. In this chapter, we review
the principle and theory of seismic wave propagation in an anisotropic
medium induced by aligned cracks, the 3-D ray series method with applications
for inhomogeneous anisotropic medium, and observations and modeling of seismic
anisotropy in fractured crustal rocks, part of which have been introduced in
our previously published papers. The method and technique defining the orientation
and density of a population of crustal cracks described in this chapter are
helpful for further understanding the damaged structure in the earth crust and
also useful in exploration of geothermal reservoirs and hydro-fracturing shale

Key Words
Seismic wave polarization, Shear-wave splitting, Anisotropicmedium, Crack-induced anisotropy, Ray tracing, Vertical seismic profiling.

Li, Y. (2016). Seismic wave propagation in anisotropic rocks with applications to defining fractures in earth crust. In 0 (Eds.), Rock anisotropy, fracture and earthquake assessment, (Chapter 1, pp. 11-141) Beijing and Boston, China and USA: China High Education Press with De Gruyter