Investigation of the structure and dynamic response of granite weathering crust slopes based on microtremor recordings: A case study of a landslide in Lishui, Zhejiang Province

Granite weathering crust slopes are widely distributed in southeastern China and are highly susceptible to mass landslides during rainy events. Investigating the structure of granite weathering crust slopes and studying the dynamic responses of these slopes are crucial for preventing and mitigating such geological disasters. This paper examines a landslide in Lishui, Zhejiang Province, with field investigations conducted in July 2019 immediately following the landslide event. The results indicate that the slope consists of a coarse-grained granite weathering layer and a granodiorite weathering layer. In November 2024, subsequent microtremor monitoring was carried out on the slope. Utilizing the horizontal-to-vertical spectral ratio (HVSR) method, the anlaysis identified distinct predominant frequencies at the top, middle, and base of the slope. Shear wave velocity inversion based on the HVSR method showed that from the exterior to the interior, the slope mainly consists of granite weathered residual soil layers and fully to moderately weathered layers, with 2 to 3 potential underground interfaces that could evolve into sliding surfaces. The slope exhibits the most significant amplification effect in the direction of the slope, and as the elevation increases, the amplification effects significantly intensify within the 3 to 22 Hz vertically and 4～60 Hz horizontally, with synchronization of amplification at the same frequencies across different stations, which is detrimental to the slope stability under dynamic loading. However, the asynchronization of amplification across different frequencies is beneficial to the stability of the slope under dynamic loading.