Upper mantle seismic anisotropy at a strike-slip boundary: South Island, New Zealand
Name
Hager EAPS Zietlow et al 2014.pdf
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3.8 MB
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Author(s)
Zietlow, Daniel W.
Sheehan, Anne F.
Molnar, Peter H.
Savage, Martha K.
Hirth, Greg
Collins, John A.
Hager, Bradford H
Date Issued
February 2014
Journal
Journal of Geophysical Research: Solid Earth
Publisher
American Geophysical Union (AGU)
Citation
Zietlow, Daniel W., Anne F. Sheehan, Peter H. Molnar, Martha K. Savage, Greg Hirth, John A. Collins, and Bradford H. Hager. “Upper Mantle Seismic Anisotropy at a Strike-Slip Boundary: South Island, New Zealand.” Journal of Geophysical Research: Solid Earth 119, no. 2 (February 2014): 1020–1040. © 2013 American Geophysical Union
Version
Final published version
Abstract
New shear wave splitting measurements made from stations onshore and offshore the South Island of New Zealand show a zone of anisotropy 100–200 km wide. Measurements in central South Island and up to approximately 100 km offshore from the west coast yield orientations of the fast quasi-shear wave nearly parallel to relative plate motion, with increased obliquity to this orientation observed farther from shore. On the eastern side of the island, fast orientations rotate counterclockwise to become nearly perpendicular to the orientation of relative plate motion approximately 200 km off the east coast. Uniform delay times between the fast and slow quasi-shear waves of nearly 2.0 s onshore continue to stations approximately 100 km off the west coast, after which they decrease to ~1 s at 200 km. Stations more than ~300 km from the west coast show little to no splitting. East coast stations have delay times around 1 s. Simple strain fields calculated from a thin viscous sheet model (representing distributed lithospheric deformation) with strain rates decreasing exponentially to both the northwest and southeast with e-folding dimensions of 25–35 km (approximately 75% of the deformation within a zone 100–140 km wide) match orientations and amounts of observed splitting. A model of deformation localized in the lithosphere and then spreading out in the asthenosphere also yields predictions consistent with observed splitting if, at depths of 100–130 km below the lithosphere, typical grain sizes are ~ 6–7 mm.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
https://doi.org/10.1002/2013JB010676
