Abstract:
Objective The MS6.2 earthquake that struck Jishishan County, Gansu Province, on December 18, 2023, triggered a series of secondary geological disasters, including landslides, collapses, and debris flows. This earthquake is considered one of the most devastating seismic events in China in recent years. The study aims to analyze the characteristics of seismicity-induced disasters in the region and identify the underlying geological factors contributing to these secondary geological hazards. Specifically, the research focuses on how the geological environment influences the development of these disasters, particularly landslides, collapses, and debris flows. This understanding will help to develop better disaster prevention and mitigation strategies for similar seismic regions. Methods To investigate these issues, the study uses a combination of field investigations, remote sensing image interpretation, and the analytic hierarchy process (AHP). The AHP was employed to evaluate the relative importance of five key factors—faults, lithology, vegetation cover, slope, and precipitation—in the formation of secondary geological hazards. The analysis also includes a detailed spatial distribution study of these factors and how they interact under seismic conditions. This multi-method approach provides a comprehensive understanding of the complex geological environment in Jishishan. Results Based on the integrated analysis, the secondary geological hazard zones of the study area are primarily concentrated along the front edge of Lajishan, closely aligned with the VIII seismic intensity zone of the Jishishan MS6.2 earthquake. Fewer hazard zones are located at the northern edge of Lijia Village, Guantan Village, and Manisigou Township. The higher-risk areas are centered around Jishishan County, extending eastward toward Lijia Village and Hanji Town. The secondary geological disaster points are concentrated in Jishishan County and the area surrounding it, particularly in valleys where Quaternary strata are abundant, forming a band-like distribution. Landslides are most prevalent in Jishishan County and Dahejia Town, where steep terrain, fragile geological structure, and significant rock weathering make the area vulnerable. The lack of vegetation exacerbates surface instability. Debris flows mainly occur in Baizang Town and around Jishishan, where steep slopes, concentrated rainfall, and abundant loose materials create ideal conditions for disaster. These debris flow sites are located near rivers or lakes, indicating that water flow and increased soil saturation are key factors triggering such events. Landslide sites are generally scattered but concentrated in areas of significant topographic change, following the Quaternary strata in valleys. These sites are denser near the Lajishan fault zone, showing the influence of fault proximity and rainfall on landslide occurrence. Each type of geological disaster exhibits distinct spatial patterns: landslides and debris flows are more likely to occur in areas with steep slopes and proximity to water bodies, while collapses tend to occur in exposed rock areas, influenced by local lithology. Evidently, the distribution of secondary geological hazards in the study area is primarily influenced by weak geological conditions, with seismic activity, vegetation, topography, and precipitation compounding the risk. Hazard zones are concentrated along the front of Lajishan, matching the VIII seismic intensity zone. The disaster sites are primarily located in valleys with dense fourth-level strata, confirming the consistency between the simulated and actual hazard zones. Conclusion To conclude, lithology was found to be the most significant factor influencing disaster formation, with a weight of 42%, followed by fault zones (26%). While precipitation had the least impact, contributing only 6%, it still played a role in increasing the risk of landslides and debris flows. The high-risk disaster areas correspond closely to the seismic intensity zone VIII, particularly around the earthquake epicenter, where the geological conditions are most conducive to these hazards. The distribution of secondary geological disasters in Jishishan is primarily controlled by the weak geological conditions of the region. Besides, compared to the Wenchuan earthquake, where disasters were concentrated along the hanging wall of reverse faults, the disaster sites in Jishishan were mainly located in the down-thrust areas of fault zones. Additionally, fewer disaster points were observed in aftershock zones, suggesting that the main shock alleviated a significant amount of tectonic stress, leading to regional stabilization. [ Significance ] This study highlights the relationship between geological factors and seismicity-induced secondary disasters in Jishishan, emphasizing the need for targeted monitoring and protective measures in areas with loose Quaternary deposits and steep slopes. The results provide valuable insight for disaster prevention strategies in Jishishan and other seismic regions with similar geological conditions.
LU S M，WU Z H，HUANG T，2025. Characteristics of geological hazard development and disaster-inducing environment of the MS6.2 earthquake in Jishishan, Gansu Province[J]. Journal of Geomechanics，31（1）：139−155. doi: 10.12090/j.issn.1006-6616.2024069.
