TY - JOUR AU - Mohiuddin Anwar, Long Maureen D. PY - 2015// TI - Mid-mantle seismic anisotropy beneath southwestern Pacific subduction systems and implications for mid-mantle deformation JO - Physics of the Earth and Planetary Interiors SP - 1 EP - 14 VL - 245 KW - Mantle deformation KW - Mid-mantle KW - Seismic anisotropy KW - Shear wave splitting KW - Subduction zones KW - N2 - Observations of seismic anisotropy can offer relatively direct constraints on patterns of mantle deformation, but most studies have focused on the upper mantle. While much of the lower mantle is thought to be isotropic, several recent studies have found evidence for anisotropy in the transition zone and uppermost lower mantle (the mid-mantle), particularly in the vicinity of subducting slabs. Here we investigate anisotropy at mid-mantle depths in the Tonga-Kermadec, Sumatra, New Britain, New Hebrides, and Philippines subduction zones using the source-side shear wave splitting technique. We measure splitting of direct teleseismic S phases originating from deep events (>300km) that have been corrected for the effect of upper mantle anisotropy beneath the seismic stations. We find evidence for considerable anisotropy at mid-mantle depths in all subduction systems studied, with delay times averaging ∼1.0–1.5s. Several measurements originating from depths greater than 600km exhibit delay times greater than 1s, suggesting a significant contribution from anisotropy in the uppermost lower mantle. We combine our results with those documented in previous studies into a quasi-global set of source-side shear wave splitting measurements that reflect mid-mantle anisotropy. We document significant variability in the dominant fast directions both within and among individual subduction systems, suggesting different deformation geometries among different subduction systems. As further constraints on the elasticity and deformation of mid-mantle minerals become available, our dataset can be used to constrain patterns of mid-mantle flow associated with subduction. SN - 0031-9201 UR - http://dx.doi.org/10.1016/j.pepi.2015.05.003 N1 - exported from refbase (http://publi.ipev.fr/polar_references/show.php?record=6152), last updated on Wed, 03 Jul 2024 19:05:41 +0200 ID - MohiuddinAnwar2015 ER -