Publication Date:
2014-04-24
Description:
Anisotropy in the Earth's upper mantle is a signature of past and present deformation. Here we present a new dataset of ˜ 50,000 uniformly processed SKS shear wave splitting measurements that probe upper mantle anisotropy beneath seismic stations in the frequency band 0.02-0.1 Hz. The dataset consists of measurements obtained at ˜ 2,000 seismic stations from ˜ 2,000 events. We identify several stations characterised by an apparent absence of shear wave splitting (so-called 'null stations'). Station averaged measurements are obtained by stacking shear wave splitting error surfaces [ Restivo and Helffrich , 1999]. The stacked dataset shows excellent agreement with a compilation of previous SKS measurements [ Becker et al ., 2012]. The average amount of splitting beneath seismic stations (after error surface stacking) is 0.8s, slightly lower than that found previously by vectorial averaging of non-null measurement splitting parameters [ Becker et al ., 2012]. The dataset disagrees, however, with an azimuthally anisotropic surface wave tomography model (DKP2005) [ Debayle et al ., 2005], suggesting that caution should be exercised when using such models for geodynamic interpretation, especially in continental regions. Studying our dataset in detail, we find evidence that flow in the asthenosphere exerts partial control over SKS splitting in orogenic regions globally. In the active orogenic environment of the western USA - where we have the densest coverage - we find evidence that shallow asthenospheric flow is guided by a wall of thick lithosphere to the east.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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