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Abstract To systematically investigate seismic azimuthal anisotropy in the Sumatra subduction zone and probe mantle dynamics associated with the subduction of the Australian Plate beneath the Sunda Plate, a total of 169 pairs of teleseismic XKS (including PKS, SKKS, SKS) and 115 pairs of localSsplitting parameters are obtained using broadband seismic data recorded at ~70 stations. Additionally, crustal anisotropy in the overriding Sunda Plate is measured by analyzing the moveout ofP‐to‐Sconversions from the Moho using a sinusoidal function. Comparison between the three sets of anisotropy measurements obtained using shear waves with different depths of origin suggests that (1) the crust of the Sunda Plate is anisotropic with mostly trench‐parallel fast orientations and a mean splitting time of 0.28 ± 0.05 s; (2) the mantle wedge is azimuthally anisotropic with dominantly trench‐parallel fast orientations and splitting times ranging from 0.22 to 0.81 s, which generally increase with the focal depth; and (3) subslab anisotropy is mostly trench‐normal beneath the fore‐arc region with an averaged splitting time of 1.48 ± 0.06 s, and becomes trench‐parallel beneath the arc and back‐arc areas with a mean splitting time of 0.33 ± 0.04 s. The resulting lateral and vertical distributions of anisotropy obtained using splitting of three types of shear waves advocate the presence of an entrained subslab flow that is deflected by the mantle transition zone. The flow enters the mantle wedge through a slab window and flows horizontally parallel to the trench.
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Receiver Function Investigations of Seismic Anisotropy Layering Beneath Southern California
Abstract Seismic azimuthal anisotropy characterized by shear wave splitting analyses using teleseismicXKSphases (includingSKS,SKKS, andPKS) is widely employed to constrain the deformation field in the Earth's crust and mantle. Due to the near‐vertical incidence of theXKSarrivals, the resulting splitting parameters (fast polarization orientations and splitting times) have an excellent horizontal but poor vertical resolution, resulting in considerable ambiguities in the geodynamic interpretation of the measurements. Here we useP‐to‐Sconverted phases from the Moho and the 410‐ (d410) and 660‐km (d660) discontinuities to investigate anisotropy layering beneath Southern California. Similarities between the resulting splitting parameters from theXKSandP‐to‐Sconverted phases from thed660 suggest that the lower mantle beneath the study area is azimuthally isotropic. Similarly, significant azimuthal anisotropy is not present in the mantle transition zone on the basis of the consistency between the splitting parameters obtained usingP‐to‐Sconverted phases from thed410 andd660. Crustal anisotropy measurements exhibit a mean splitting time of 0.2 ± 0.1 s and mostly NW‐SE fast orientations, which are significantly different from the dominantly E‐W fast orientations revealed usingXKSandP‐to‐Sconversions from thed410 andd660. Anisotropy measurements using shear waves with different depths of origin suggest that the Earth's upper mantle is the major anisotropic layer beneath Southern California. Additionally, this study demonstrates the effectiveness of applying a set of azimuthal anisotropy analysis techniques to reduce ambiguities in the depth of the source of the observed anisotropy.
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- Award ID(s):
- 1830644
- PAR ID:
- 10370955
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 123
- Issue:
- 12
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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