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Published byBarnaby Nelson Modified over 8 years ago
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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 2 Institute of Geology & Min. Res., Chengdu, China Geodynamics of Indentor Corners
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Map of the Eastern part of the Tibet plateau Study area
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LOCATION OF THE SEISMIC ARRAY
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Shear-wave splitting or birefringence t=L* Approximate expression for small anisotropy Fast polarization ( Delay time { 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). Objectives: Assess the presence of seismic anisotropy and illuminate important questions about the processes of deformation in the Earth
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Where do we have evidence of anisotropy within the Earth? Causes of anisotropy? - Thin isotropic layers with different velocities - Aligned, fluid fractures or cracks - LPO of lower crustal phyllosilicates minerals - LPO of mantle minerals (Olivine) CRUST MANTLE
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Lattice-preferred orientations of olivine The splitting technique can provide important information about mantle strain field. Pole figures of crystallographic orientation of deformed olivine aggregates - A-axis parallel to ductile shear - S-wave polarization parallel to a-axis
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Paths of seismic phases used for the splitting analysis
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Seismograms showing the arrival of different phases Local event SKS The bulk of the evidence for mantle seismic anisotropy comes from observations of SKS and SKKS phases.
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Seismograms filtered appropriately for SKS phases
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Example of SKS splitting analysis
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From Savage, 1999 How do you better constrain the depth of anisotropy of the observable splitting? We can also use other geophysical methods!
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Physical processes for producing mantle anisotropy From Silver, 1996.
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Pacific events Bolivia event Topographic map displaying splitting results from two distinct azimuths
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Topographic map showing the preliminary splitting parameters at all the stations of the Eastern Syntaxis Experiment
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Comparing preliminary GPS results and splitting direction GPS measurements are courtesy of Liu Yuping and Peter Koons
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Complex anisotropic structure at the LHASA station (LSA)
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Preliminary SKS relative traveltime analysis
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