Subsurface imaging based on polarization analysis of microtremor Rayleigh waves
Qingling Du , Qian Xu , Nan Guo , Shuai Liu , Shijie Liu , Denghui Gao
Journal of Seismic Exploration ›› 2026, Vol. 35 ›› Issue (1) : 83 -100.
The precise identification of adverse geological bodies, such as goafs, karst cavities, and faults, is crucial for engineering safety and economic viability. However, conventional drilling methods suffer from high costs, limited coverage, and the risk of overlooking anomalies. While existing geophysical techniques can address drilling’s limitations, they are often constrained by non-uniqueness and insufficient resolution. To address these challenges, this paper proposes a novel technique for stratigraphic evaluation based on the polarization analysis of microtremor surface waves, aiming to improve the accuracy and efficiency of identifying dynamic site parameters in complex geological settings. We systematically validated the feasibility of using the elliptical polarization ratio of Rayleigh waves for subsurface characterization through theoretical analysis and field data. Numerical simulations confirmed that the method can clearly identify localized geological anomalies under noise-free conditions. For field data processing, we developed a workflow to extract Rayleigh waves with a high signal-to-noise ratio from microtremors. This workflow isolates valid wave components using principal frequency filtering and directional discrimination, while mitigating noise impact on dispersion estimation. The final polarization ratio profile strongly correlated with magnetotelluric resistivity data, successfully imaging goafs, fractured zones, and bedrock interfaces. Stacking codirectional wave events further enhanced deep structural resolution and resulted in consistency. In conclusion, this study demonstrates that the polarization-based method is a feasible, flexible, and promising tool for engineering applications, offering a reliable foundation for fine-scale site characterization.
Microtremor Rayleigh wave / Elliptical polarization ratio / Site characterization / Numerical simulations
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