TY - JOUR
T1 - Mapping P-wave azimuthal anisotropy in the crust and upper mantle beneath the United States
AU - Huang, Zhouchuan
AU - Zhao, Dapeng
N1 - Funding Information:
We thank the data center of the EarthScope/USArray project for providing the high-quality arrival-time data used in this study. This work was partially supported by the Global-COE Program of Earth and Planetary Sciences of Tohoku University, a grant (Kiban-S11050123) from Japan Society for the Promotion of Science to D. Zhao and a grant (No. 41204040) from National Natural Science Foundations of China to Z. Huang. Prof. G. Helffrich (the Editor) and two anonymous referees provided very thoughtful review comments that have improved the manuscript. We appreciate helpful discussions with Drs. You Tian, Jian Wang and Wei Wei. The figures are made using GMT ( Wessel and Smith, 1998 ).
PY - 2013/12
Y1 - 2013/12
N2 - Much progress has been made on revealing seismic structure and mantle dynamics beneath the United States (US) with the EarthScope/USArray project. Seismic anisotropy revealed by shear-wave splitting studies provides important constraints on constructing geodynamic models with regard to the seismic images, but the shear-wave splitting observations have poor vertical resolution and so their interpretations are often not unique. In this work we used a large number of arrival-time data from local and distant earthquakes recorded by the USArray to determine the first P-wave azimuthal anisotropy tomography of the crust and upper mantle beneath the US. Our results show that fast velocity directions (FVDs) in the lithosphere under the tectonically active areas correlate well with the surface tectonic features, suggesting that the P-wave anisotropy mainly reflects the present deformation. A circular pattern of the FVDs centered in the Great Basin is revealed, which is well consistent with the specific circular shear-wave splitting observations there, suggesting that the anisotropy occurs in the crust and uppermost mantle. In contrast, beneath the stable cratonic region, the FVDs revealed by this study differ from the shear-wave splitting observations but consistent with the features of gravity and magnetic anomalies, indicating that the P-wave FVDs mainly reflect the fossil anisotropy in the lithosphere, whereas the S-wave splitting observations mainly reflect the significant anisotropy in the asthenosphere. The present results shed new light on the seismic anisotropy in the crust and upper mantle and provide new constraints on constructing geodynamic models beneath the US.
AB - Much progress has been made on revealing seismic structure and mantle dynamics beneath the United States (US) with the EarthScope/USArray project. Seismic anisotropy revealed by shear-wave splitting studies provides important constraints on constructing geodynamic models with regard to the seismic images, but the shear-wave splitting observations have poor vertical resolution and so their interpretations are often not unique. In this work we used a large number of arrival-time data from local and distant earthquakes recorded by the USArray to determine the first P-wave azimuthal anisotropy tomography of the crust and upper mantle beneath the US. Our results show that fast velocity directions (FVDs) in the lithosphere under the tectonically active areas correlate well with the surface tectonic features, suggesting that the P-wave anisotropy mainly reflects the present deformation. A circular pattern of the FVDs centered in the Great Basin is revealed, which is well consistent with the specific circular shear-wave splitting observations there, suggesting that the anisotropy occurs in the crust and uppermost mantle. In contrast, beneath the stable cratonic region, the FVDs revealed by this study differ from the shear-wave splitting observations but consistent with the features of gravity and magnetic anomalies, indicating that the P-wave FVDs mainly reflect the fossil anisotropy in the lithosphere, whereas the S-wave splitting observations mainly reflect the significant anisotropy in the asthenosphere. The present results shed new light on the seismic anisotropy in the crust and upper mantle and provide new constraints on constructing geodynamic models beneath the US.
KW - Azimuthal anisotropy
KW - Deformation
KW - Lithosphere
KW - Seismic tomography
KW - Shear-wave splitting
KW - USArray
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U2 - 10.1016/j.pepi.2013.10.003
DO - 10.1016/j.pepi.2013.10.003
M3 - Article
AN - SCOPUS:84888293734
VL - 225
SP - 28
EP - 40
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
SN - 0031-9201
ER -