Abstract
To investigate the spatial and temporal variations of seismic azimuthal anisotropy in the vicinity of the conjugate fault network activated by the 4 July 2019 (UTC) M6.4 foreshock and the 6 July 2019 M7.1 mainshock in Ridgecrest, California, a total of 1,470 shear wave splitting measurements were obtained from local events recorded by five seismic stations over the period of July 2019 to January 2020. The results suggest a strong asymmetry in anisotropy forming mechanisms across the NW-SE striking Eastern Little Lake Fault, which is the main fault of the area. In the area located to the northeast of the main fault, the observed fast orientations are dominantly N-S, which is parallel to the maximum horizontal compressive stress. In the area surrounding the main fault, the fast orientations are primarily parallel to the strikes of multiple fault zones including the main fault and the crossing faults, rather than solely consistent with that of the main fault, which may indicate along-strike variations in fault strength of the main fault. To the southwest of the main fault, the observed anisotropy is jointly controlled by faults or regional stress. The observed NE-SW-oriented anisotropy in the vicinity of two previously proposed blind faults confirms the existence of faults. The splitting times of anisotropic areas with different inducements are independent of the focal depths, suggesting that either the stress- or structure-induced anisotropy is mostly located in a shallow layer in the top several kilometers. A nearly 90-degree switch in the fast orientations and greatly reduced splitting times from a group of nearby earthquakes may indicate fault zone healing.
Recommended Citation
Y. Jia et al., "Spatial and Temporal Variations of Seismic Azimuthal Anisotropy Following the 2019 Ridgecrest Earthquake Sequence in Southern California," Earth and Planetary Science Letters, vol. 644, article no. 118920, Elsevier, Oct 2024.
The definitive version is available at https://doi.org/10.1016/j.epsl.2024.118920
Department(s)
Geosciences and Geological and Petroleum Engineering
Publication Status
Open Access
Keywords and Phrases
2019 ridgecrest earthquake sequence; Crustal deformation; Fault zone healing; Seismic anisotropy; Shear wave splitting
International Standard Serial Number (ISSN)
0012-821X
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2024 Elsevier, All rights reserved.
Publication Date
15 Oct 2024
Comments
Natural Science Foundation of Zhejiang Province, Grant LR24D060001