Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 41, Issue 10, Pages 3438-3446Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014GL059943
Keywords
Peru; Nazca Ridge; Shear Wave Splitting; Flat Subduction; Seismic Anisotropy; Mantle Deformation
Categories
Funding
- National Science Foundation [EAR-0943962, EAR-0944184, EAR-0943991]
- Directorate For Geosciences
- Division Of Earth Sciences [0943962] Funding Source: National Science Foundation
- Directorate For Geosciences
- Division Of Earth Sciences [0943991, 0944184] Funding Source: National Science Foundation
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The dynamics of flat subduction, particularly the interaction between a flat slab and the overriding plate, are poorly understood. Here we study the (seismically) anisotropic properties and deformational regime of the mantle directly above the Peruvian flat slab. We analyze shear wave splitting from 370 local S events at 49 stations across southern Peru. We find that the mantle above the flat slab appears to be anisotropic, with modest average delay times (similar to 0.28 s) that are consistent with similar to 4% anisotropy in a similar to 30 km thick mantle layer. The most likely mechanism is the lattice-preferred orientation of olivine, which suggests that the observed splitting pattern preserves information about the mantle deformation. We observe a pronounced change in anisotropy along strike, with predominately trench-parallel fast directions in the north and more variable orientations in the south, which we attribute to the ongoing migration of the Nazca Ridge through the flat slab system.
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