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Insight into the lithospheric structure and deformation in Eastern

Geodynamics of Indentor Corners. Insight into the lithospheric structure and deformation in Eastern Tibet from splitting and traveltime variations of core phases. S. Sol, A. Meltzer, B. Zurek, X. Zhang, J. Zhang 1 Lehigh University, Bethlehem, PA

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Insight into the lithospheric structure and deformation in Eastern

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  1. Geodynamics of Indentor Corners Insight into the lithospheric structure and deformation in Eastern Tibet from splitting and traveltime variations of core phases S. Sol, A. Meltzer, B. Zurek, X. Zhang, J. Zhang 1Lehigh University, Bethlehem, PA 2Institute of Geology & Min. Res., Chengdu, China

  2. Map of the Eastern part of the Tibet plateau Study area

  3. LOCATION OF THE SEISMIC ARRAY

  4. Approximate expression for small anisotropy t=L* Shear-wave splitting or birefringence As a shear (S) wave propagates through an anisotropic medium, it will split into two roughly perpendicularly polarized shear waves and its components will propagate at different speeds, resulting in a differential arrival time (split time, t) between the components (shear-wave splitting or birefringence). { Fast polarization (F) Delay time Objectives: Assess the presence of seismic anisotropy and illuminate important questions about the processes of deformation in the Earth

  5. Where do we have evidence of anisotropy within the Earth? Causes of anisotropy? CRUST • - Thin isotropic layers • with different velocities • - Aligned, fluid fractures or cracks • - LPO of lower crustal phyllosilicates minerals MANTLE - LPO of mantle minerals (Olivine)

  6. Lattice-preferred orientations of olivine Pole figures of crystallographic orientation of deformed olivine aggregates - A-axis parallel to ductile shear - S-wave polarization parallel to a-axis The splitting technique can provide important information about mantle strain field.

  7. Paths of seismic phases used for the splitting analysis

  8. Local event SKS The bulk of the evidence for mantle seismic anisotropy comes from observations of SKS and SKKS phases. Seismograms showing the arrival of different phases

  9. Seismograms filtered appropriately for SKS phases

  10. Example of SKS splitting analysis

  11. How do you better constrain the depth of anisotropy of the observable splitting? From Savage, 1999 We can also use other geophysical methods!

  12. Physical processes for producing mantle anisotropy From Silver, 1996.

  13. Topographic map displaying splitting results from two distinct azimuths Pacific events Bolivia event

  14. Topographic map showing the preliminary splitting parameters at all the stations of the Eastern Syntaxis Experiment

  15. Comparing preliminary GPS results and splitting direction GPS measurements are courtesy of Liu Yuping and Peter Koons

  16. Complex anisotropic structure at the LHASA station (LSA) F=50 F=30-40 F=25 F=-7 F=60 F=-30

  17. Preliminary SKS relative traveltime analysis

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