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Shear Wave Splitting: Understanding, History, and Applications

Delve into the concept, definitions, history, and applications of shear wave splitting in seismic birefringence. Explore common misunderstandings and conclusions drawn from this phenomenon, including its potential in earthquake prediction and CO2 injection mapping.

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Shear Wave Splitting: Understanding, History, and Applications

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  1. Introduction to Shear Wave Splitting Erin Elliott Guofeng Yuan February 26, 2010

  2. Outline • Concept • Definitions • History • Applications • Common Misunderstandings • Conclusions

  3. What is Shear Wave Splitting? • When a polarized shear-wave enters an anisotropic medium, it splits into two quasi shear-waves (fast and slow).

  4. Shear Wave Splitting (Seismic birefringence) http://garnero.asu.edu/research_images/anis/garnero_splitting.gif

  5. History

  6. Definitions • Microcrack • Azimuthally Aligned • Polarization Diagrams

  7. Microcracks Crack density

  8. Azimuthally Aligned • the angles that the arrivals or waves make with a reference point are all equal. • The waves are approximately parallel: http://en.wikipedia.org/wiki/Azimuth

  9. Polarization Diagrams(Hodograms) • Displays a 2-D projection of the trajectory of a point moving in space. • a cross plot of two components of motion over a time window. http://www.crewes.org/ResearchLinks/ExplorerPrograms/Hodogram/Hodogram.html

  10. Applications • Possible earthquake prediction • for earthquakes M 1.7 to M 7.7 • CO2 Injection mapping • in fractured carbonate reservoirs

  11. Common Misunderstandings • Polarizations of split shear waves are orthogonal • Crack anisotropy always decreases with depth as fluid filled cracks are closed by lithostatic pressure. • Signal-to-noise ratios of shear-wave splitting above small earthquakes can be improved by stacking.

  12. Conclusion • Stress aligned fluid-saturated microcracks are the predominant cause of the nearly universal observations of azimuthally aligned shear wave splitting both in the earth’s crust and in the upper mantle.

  13. Questions?

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