The role of seismic triggering in a deep-seated mudstone landslide, China: Historical reconstruction and mechanism analysis

Deep-seated mudstone landslides are widely distributed in northwest China. The Zhengjiamo landslide occurred in 734 CE near Taijing, Tianshui region. It was triggered by the main shock of the historical Ms = 7.0734 CE earthquake. The earthquake also induced a wide range of landslides in this area, with hundreds of fatalities and many houses destroyed by landslide debris. Based on a detailed field survey, borehole data, and mapping, a detailed geological reconstruction of the slope was achieved and the geo-mechanical features of the claystone involved in the landslide were obtained. Using the Particle Flow Code to simulate the mechanism of the Zhengjiamo landslide, the features of the landslide dynamics were obtained using a 5-stage model. During the landslide process, the slip mass at the front and upper edges exhibited higher mobility than at the rear and bottom edges. Furthermore, the contact bond strength of the sliding body gradually weakened. The model indicates that the particle bond strength has a larger influence on the maximum runout distance and landslide debris morphology than the type of weak intercalated layers. The slip mass presented a rotational slide pattern and remained on the slip plane throughout the sliding process. Finally, the earthquake uplifted the slope toe, which prevented the slip mass from gliding. The modelled scenario provided a reasonably good fit to the actual topography, verifying the modelling results. After the historical earthquake, with the clay minerals swelling and shrinking under rainfall and efflorescence conditions, the structure of the soft rock changed, contributing to the weakening of the sliding rock mass. The landslide gradually crept and evolved to its current topography.