1. The document discusses seismic anisotropy, which is when seismic wave speeds vary depending on propagation direction through a medium. 2. Anisotropy in the mantle is caused by lattice preferred orientation of intrinsically anisotropic olivine crystals aligned by mantle flow. 3. Shear wave splitting is an indicator of anisotropy, where the fast and slow shear waves arrive at different times and have different polarizations, revealing information about stress and deformation.

1. Solid Earth Geophysics-Geop503 Ali Oncel [email_address] Department of Earth Sciences, KFUPM Anisotropy and Attenuation Reading: Fowler Chapter 8- Section 8.1

3. Reason to study Anisotropy? http://www.patentstorm.us/patents/5142501-description.html Crampin and Bush (1986) also pointed out that vertical S-wave birefringence might provide a useful tool for reservoir development. The polarization direction of the fast S-wave in simple cases gives the direction of maximum horizontal compressive stress, a quantity much in demand by those who induce fractures in reservoirs by techniques such as hydraulic fracturing Available evidence, (Winterstein, 1990) including offset VSP information supports the notion that the vertical S-wave birefringence is caused by horizontal stresses, and that the polarization direction of the fast S-wave lies in the direction of maximum horizontal compressive stress , even when subsurface structures are steeply dipping.

5. Anisotropy Shape-preferred orientation anisotropy A shear wave can be split into two pulses, each with a different polarity and traveling at a different speed Anisotropic materials cause seismic waves traveling through them to travel faster or slower depending on their direction. Shear-wave Splitting

7. a axis is fastest direction This is also dominant slip direction, so olivine crystals align in direction of plastic flow OLIVINE IS HOMEGENOUS BUT ANISOTROPIC Lattice-preferred orientation (LPO) anisotropy Babuska and Cara, 1991

8. East West South PROPAGATION DIRECTION V P anomaly (km s -1 ) Central Pacific Morris et al., (1969) JGR . ANISOTROPY FROM RELATIVE PLATE MOTION Stein 2003, pp. 180

10. Attenuation of Seismic Waves Q= Quality Factor= 2 π x elasticity energy stored in the wave Energy lost in one cycle or wavelength

11. From: Panning and Romanowicz, 2004 Radial Anisotropy Depth = 250 km

12. Under Pacific: transverse isotropy versus Q Anisotropy versus attenuation Central Pacific

13. Anisotropy See: pp. 346-348 of Fowler’s book Garnero, Ann. Rev. 2000 “ Scenario for CMB”

14. From: Sean Ford, 2004

15. From: Christine Thomas , 2004

16. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. B11, 2274, 2002 http://www.liv.ac.uk/earth/Staff/academic/TineThomas.htm For more information:

17. From: Sean Ford, 2004