Analysis of the Electrical Structure and Fluid Content of the Southern San Andreas Fault
Li Bao-Chun, Sun Shao-Huai*, Tai Bao-Qiang,*, Gao Cheng, Dong Ji-En, Zhang Kuo,
Zhang Xin-Yi, Kang Zhao-Yuan, and Guo Xiang-Guo
1. School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China
2. School of Resources and Environmental Engineering, Inner Mongolia University of Technology, Hohhot 010051, Inner Mongolia, China
3. Inner Mongolia Engineering Research Center of Geological Technology and Geotechnical Engineering, Inner Mongolia University of Technology, Hohhot 010051, China
4. Geological Survey of Qinghai, Xining 810000, China
Abstract：
The study of the electrical structure and fl uid content of the southern San Andreas Fault (SSAF) plays a significant role in understanding the geological processes and earthquake genesis. The paper analyzes the Bahr skew and G-B decomposition from magnetotelluric sounding data in the SSAF to determine the strike direction is north-eastward 135°. Using the Nonlinear Conjugate Gradient algorithm, a reliable 2D electrical structure model was obtained. The Mission Creek and Banning faults, components of the SSAF, exhibit high conductivity within the crust, whereas the Eastern Transverse Ranges to the northeast of the fault show high resistivity characteristics. By integrating the modified Archie's law, the relations between conductivity, temperature, salinity, and fl uid content were established, leading to conductivity-temperature and conductivity-fluid content relationships. Combining the results from the electrical structure model and fluid model of the SSAF, it is inferred that the fluid content in the high-conductivity crust reach up to 20 %. When the fl uid salinity is 10 wt%, the fluid content required to achieve the same high bulk conductivity reduces to 2 %. A comparison of the electrical structure and focal depth of the Tan-Lu Fault Zone reveals that the collision between the low-viscosity fl uids of the Mission Creek and Banning faults and the rigid Eastern Transverse Ranges contributes to the earthquake in the SSAF.
2025, Vol. 22 
