Seismic anisotropy is sensitive to the alignment of minerals, fluid-filled cracks and fractures caused by fault deformation, thus providing a signature of fault deformation, especially in the aseismic layer. In this study, we use seismic traveltime anisotropy tomography to study the spatial distribution of azimuthal anisotropy in the region of the 2013 Mw 6.6 Lushan earthquake. Our analysis reveals both stress-induced and structure-controlled seismic anisotropy mechanisms. The distribution of seismicity and anisotropy clearly delineates conjugate faults in the seismogenic zone between depths of 8 and 15 km. Two near-vertical stripes or zones of strong seismic anisotropy reveal the continuation of these faults into the diagenetic or overlying aseismic crust. The anisotropic corridors associated with the conjugate faults are interpreted in terms of the crystal preferred orientation of fault rock minerals, which may be enhanced by shear-band compaction. Our results demonstrate how seismic anisotropy can provide new insights into fault deformation.
Bibliographical noteFunding Information:
The authors are grateful for Donna Eberhart‐Phillips for sharing her original seismic traveltime anisotropy code with us, which is adapted for our study. The authors also thank Associate Editor Victor Tsai and two anonymous reviewers for their helpful comments. This work is supported by the National Key R&D Program of China under Grant 2018YFC1504102, the National Natural Science Foundation of China (grants 42004034 and U1839205) and the China Scholarship Council award 201606340073.
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