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Multistage tectonic evolution of the Tanlu fault: Insights from upper crustal azimuthal anisotropy of the Chao Lake segment
  • Song Luo,
  • Huajian Yao
Song Luo
University of Science and Technology of China

Corresponding Author:songluo@ustc.edu.cn

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Huajian Yao
University of Science and Technology of China
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The Tanlu fault is the largest strike-slip fault in eastern China. It has experienced multiple episodes of tectonic activity suggested mostly by near-surface geological analysis. However, little evidence comes from deformation at different depths in the crust. This study presents a three-dimensional (3-D) high-resolution upper crustal azimuthally anisotropic model of shear-wave velocity beneath the Chao Lake segment of the Tanlu fault zone (TFZ-CL) using surface wave dispersion data (0.5–12 s) extracted from ambient seismic noise. The results show that fast directions of azimuthal anisotropy are consistent with local geological units, hence interpreted as shape-preferred orientations (SPOs). A special depth-dependent anisotropic pattern is revealed beneath eastern Chao Lake, where the fast directions vary from nearly NE-SW at shallow depths, to NNE-SSW or nearly N-S at intermediate depths and back to NE-SW at great depths. The anisotropic model is combined with other previously published datasets to construct a deformation model at multiple depths. The deformation model suggests that lithospheric deformation is decoupled from the asthenosphere beneath the TFZ-CL, implying that the deep tectonic setting could have changed dramatically since the Mesozoic. By connecting the new anisotropic model and the local tectonic episodes, we further propose a four-stage tectonic evolution model of the TFZ-CL. The model can well interpret the generation of anisotropies, especially the specific anisotropic pattern beneath eastern Chao Lake, providing new evidence of deformation at great depths to support the multistage tectonic episodes along the Tanlu fault.
May 2021Published in Tectonophysics volume 806 on pages 228795. 10.1016/j.tecto.2021.228795