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Introduction to Shear Wave Splitting

Introduction to Shear Wave Splitting. Erin Elliott Guofeng Yuan February 26, 2010. Outline. Concept Definitions History Applications Common Misunderstandings Conclusions. What is Shear Wave Splitting?.

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Introduction to Shear Wave Splitting

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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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