This study addresses the key scientific problem of urban safety in complex, hazard-inducing geological environments by focusing on representative towns in the Three Gorges Reservoir area. Through the integrated use of field investigations, numerical simulations, and multivariate statistical analysis, we developed a comprehensive model for assessing geological safety risk in reservoir-area towns. A four-tier deep safety evaluation system was constructed for two types of hazard-inducing geological environments, and a classification scheme for shallow susceptibility was proposed. On this basis, a five-tier integrated urban geological safety risk evaluation model was established that combines deep safety level, engineering sensitivity, shallow susceptibility, and prevention difficulty. The model exhibited strong performance (pseudo R² ≥ 0.914, p < 0.001) and indicates that risk is predominantly moderate (Grade III), with 85.7% of the 21 representative areas in Wushan, Fengjie, and other “2 + 4” towns falling into this category. Overall, the results provide an operational tool to support disaster risk reduction, risk-informed land-use governance, and resilient infrastructure planning, thereby contributing to sustainable urban development in reservoir-side mountainous regions.

The instability of soil slope boulders represents a prevalent geological hazard, characterized by its sudden onset and significant threats to engineering safety. However, the burial depth of boulders, a critical parameter for stability assessment, poses challenges for direct measurement. To facilitate rapid and accurate stability evaluations, this study introduces a method for assessing soil slope boulder stability based on natural vibration frequency. By simplifying the interaction between the boulder and the surrounding soil into a multi-degree-of-freedom spring-mass vibration model, we derive a dynamic characteristic model for the boulder. This model integrates the Limit Equilibrium Method with the dynamic framework to establish a stability evaluation model predicated on natural vibration frequency. The study identifies two primary failure modes for boulders: shear-sliding and rotational-toppling types. Utilizing the proposed model, we elucidate the quantitative relationships among natural vibration frequency, boulder burial depth, and boulder mass. Experimental investigations with boulder models of varying sizes demonstrate a nonlinear relationship between natural vibration frequency and both burial depth and mass. By combining the model with the Limit Equilibrium Method, we derive a formula for calculating the safety factor, which is validated through engineering case studies. The findings reveal that the calculated safety factor agrees well with numerical simulation results, thereby confirming the model’s applicability in practical engineering contexts. This study establishes a robust theoretical framework for monitoring and preventing geological disasters associated with the instability of boulders on soil slopes.