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| Titel |
Absolute Plate Velocities from Seismic Anisotropy |
| VerfasserIn |
Corné Kreemer, Lin Zheng, Richard Gordon |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107718
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| Publikation (Nr.) |
 EGU/EGU2015-7431.pdf |
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| Zusammenfassung |
| The orientation of seismic anisotropy inferred beneath plate interiors may provide a means to
estimate the motions of the plate relative to the sub-asthenospheric mantle. Here we
analyze two global sets of shear-wave splitting data, that of Kreemer [2009] and an
updated and expanded data set, to estimate plate motions and to better understand the
dispersion of the data, correlations in the errors, and their relation to plate speed.
We also explore the effect of using geologically current plate velocities (i.e., the
MORVEL set of angular velocities [DeMets et al. 2010]) compared with geodetically
current plate velocities (i.e., the GSRM v1.2 angular velocities [Kreemer et al.
2014]).
We demonstrate that the errors in plate motion azimuths inferred from shear-wave
splitting beneath any one tectonic plate are correlated with the errors of other azimuths from
the same plate. To account for these correlations, we adopt a two-tier analysis:
First, find the pole of rotation and confidence limits for each plate individually.
Second, solve for the best fit to these poles while constraining relative plate angular
velocities to consistency with the MORVEL relative plate angular velocities. The
SKS-MORVEL absolute plate angular velocities (based on the Kreemer [2009] data set)
are determined from the poles from eight plates weighted proportionally to the
root-mean-square velocity of each plate. SKS-MORVEL indicates that eight plates (Amur,
Antarctica, Caribbean, Eurasia, Lwandle, Somalia, Sundaland, and Yangtze) have angular
velocities that differ insignificantly from zero. The net rotation of the lithosphere is
0.25±0.11º Ma-1 (95% confidence limits) right-handed about 57.1ºS, 68.6ºE. The
within-plate dispersion of seismic anisotropy for oceanic lithosphere (Ïă=19.2Ë ) differs
insignificantly from that for continental lithosphere (Ïă=21.6Ë ). The between-plate
dispersion, however, is significantly smaller for oceanic lithosphere (Ïă=7.4Ë ) than for
continental lithosphere (Ïă=14.7Ë ). Two of the slowest-moving plates, Antarctica
(vRMS=4 mm a-1, Ïă=29Ë ) and Eurasia (vRMS=3 mm a-1, Ïă=33Ë ), have two of
the largest within-plate dispersions, which may indicate that a plate must move
faster than ≈5 mm a-1 to result in seismic anisotropy useful for estimating plate
motion.
We will investigate if these relationships still hold with the new expanded data set and
with the alternative set of relative plate angular velocities.
We have found systematic differences between the SKS orientations and our predicted
plate motion azimuths underneath the Arabia plate, which suggests to us either plate-scale
mantle flow process not directly associated with that plate’s absolute motion or intrinsic
lithospheric anisotropy. We will discuss more of such discrepancies underneath other plates
using the enlarged data set. |
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