Study on distribution law of geological disasters in karst mountainous area of east Yunnan

ZHANG Jie; ZHANG Weifeng; WEI Lei; DAI Xusheng; ZHANG Wenjun

doi:10.11932/karst20240612

Abstract：Based on a comprehensive and detailed investigation,coupled with a risk assessment of geological disasters at a scale of 1∶50,000 in the study area,this paper focuses on the unique characteristics of high mountain valleys and karst rock mountains prevalent within the region.Through a combination of data statistics and qualitative analysis,the distribution patterns and laws of geological disasters in the study area are meticulously elaborated in terms of landform,slope structure type,geological structure,geological engineering,and rock formation. The findings are listed as followings:(1)The terrain in northeast Yunnan is characterized by significant relief,with deep river valleys predominantly located along the plateau edges and valley slopes.Consequently,the distribution of geological disasters gradually diminishes from north to south,with a mean density of 8.62 per 100 km2.The northern alpine valleys and valley slope areas exhibit the most developed geological disasters,which are approximately 2 to 3 times more numerous than those in the central plateau basin. (2)Geological disasters are more prevalent in the geomorphic units dominated by the edges of plateaus and slopes of river valleys,with a total of 3,161 occurrences,which accounts for 29.67%of all recorded disasters.The geological disasters are not developed in the plateau areas of central and east Yunnan,where the plateau morphology is relatively intact and the terrain is gentle,with only 87 occurrences,accounting for 0.82%of the total disasters. (3)The geological disasters in the study area are mainly distributed in sections with slopes of 10°-30°,totaling of 7,028 occurrences,which account for 66.62%of all geological disasters.In contrast,the sections with slopes greater than 40° exhibit the fewest geological disasters,with only 797 occurrences,representing 7.55%of the total.Additionally,geological disasters in the study area are primarily concentrated in slope sections with orientations of 90°-135°,225°-270°,and 270°-315°,totaling 4,249 occurrences,which account for 39.88%of the overall.These disasters generally extend from north to south and west,demonstrating a correlation with the northeast-to-south and north structural patterns. (4)Geological disasters predominantly occur at the intersections of fault zones or in regions where the orientation of the primary faults changes.These disasters tend to be distributed in a linear or belt-like patterns.When faults remain continuously active,signs of multiple disasters events become apparent.The distribution of geological disasters correlates with structural features,including the orientation of faults,and the dip direction of slopes.Geological disasters are arranged in an imbricated pattern on both sides of the main controlling faults.In the case of strike-slip reverse faults,the distribution of geological disasters exhibits a notable"upper plate effect".Particularly,under seismic activities,the frequency of geological disasters on the upper plate is significantly greater than that on the lower plate. (5)In the study area,geological disasters are most prevalent in dip-slope formations that contain weak interlayers of mudstone and shale,with a total 2,995 occurrences,accounting for 31.94%of all recorded disasters.In contrast,slopes formations with orthogonal structures lack natural medium interfaces,which hinders the formation of continuous structural sliding surfaces.Consequently,geological disasters are less common in these areas,with only 901 occurrences,representing 9.61%of the total number of disasters. (6)The carbonate group containing weak interlayers is more susceptible to the development of joint fissures under tectonic forces.Surface water and groundwater can easily infiltrate these joint fissures,leading to the hydration and softening of the interlayers.Over time,this process may evolve into a slip zone for rock falls or landsides,resulting in a disaster-prone structural formation characterized by being solid and heavy on top,and soft and light below.This rock group is where geological disasters are most prevalent in the study area.The findings from this study can provide a geological foundation for comprehensive prevention and control of geological disasters,as well as a foundation for land use planning and regulation in the study area.