East Antarctic Seismic Anisotropy from Shear-wave Splitting Analysis of AGAP Seismograms
Abstract
Energetic teleseismic PKS, SKS and SKKS phases are used to constrain the orientation and magnitude of upper mantle seismic anisotropy in East Antarctica. As part of the AGAP/GAMSEIS deployment, 26 broadband seismic stations were installed over 2 field seasons and are centered over the Gamburtsev Subglacial Mountains in two linear arrays. Drawing from 348 candidate events, we analyzed 7,872 unique event-station pairs. Analysis windows were chosen using the automated methodology of Teanby et. al. [2004] which in turn employs the eigenvalue method of Silver and Chan [1988]. Each phase was individually analyzed for quality control. High-quality results from each station were then stacked to obtain best-fit splitting parameters; only 291 individual phases from original data were of significant quality to merit this further analysis. Individual measurements were qualitatively ranked and categorized using the methodology of Barklage et al. [2009]. Our array is generally located over thick and old continental lithosphere and shows a wide range of delay times (0.3 to 1 s). Splitting directions indicate the existence of 2 or more distinct tectonic regimes in East Antarctica. Splitting parameters along the north-striking array through the heart of the mountains orient perpendicular to magnetic anomalies seen in McLean et. al. [2009]. Fast directions do not seem to show any correlation with absolute plate motion vectors, suggesting fabric generation via ancient orogenic event(s). Indeed, we interpret the seismic anisotropy as a manifestation of strain-induced lattice-preferred orientation caused by large-scale deformational episodes. Shear-wave splitting studies provide methods for extending seismology into the Proterozoic and Archaean and for resolving the deformational history of a continental craton 98% of which is covered by ice.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMDI13A1849H
- Keywords:
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- 0799 CRYOSPHERE / General or miscellaneous;
- 1236 GEODESY AND GRAVITY / Rheology of the lithosphere and mantle;
- 7208 SEISMOLOGY / Mantle;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general