Research On The Correlation Mechani Sm Between Site Safety And Rural Se Ttlement Distribution In Areas With Frequent Earthquakes

Due to the perennial influence of earthquake,landslide,collapse and other geological disasters,the safety of the site selection in Ludian County,Yunnan Province is greatly threatened.However,in mountainous and rural areas,most of the site selection failed geological prospecting,resulting in unreasonable site selection planning and lack of effective engineering means,weak seismic capacity,frequent collapses and landslides.Villagers living in mountainous areas often choose to move their settlements to areas with higher site safety because of the destruction and casualties caused by disasters,which has a great impact on the distribution of traditional villages in mountainous areas.Therefore,the study of the correlation mechanism between site safety and rural settlement distribution in multi-seismic mountainous areas is of great significance to the location and layout of villages.In this study,through the methods of on-the-spot investigation,standard consultation and previous research,37 kinds of site safety factors are selected from the aspects of topography and geomorphology,stratigraphic geology and seismic effect parameters according to different standards.and according to the theoretical analysis of the principles of comparability,uniqueness and maneuverability,the site safety factors suitable for Ludian County are screened and selected.Based on the theory of point density,nearest neighbor index and nuclear density,the relationship between village settlement distribution and site safety factors in Ludian County from1642 to 1980 is studied from the aspects of quantity,new quantity,point density and so on.1.From the seismic effect parameters:（1）when the historical maximum seismic intensity decreases in the interval interval,the new settlement point increases,and when the historical maximum seismic intensity increases in the interval interval,the new settlement point decreases.（2）in the annual interval with the least earthquake,the most new settlement points are added in the 3km buffer zone nearest to the fault zone.In the strong seismic intensity and frequent annual interval,the new settlement points are concentrated in the area away from the fault zone 6km and 9km.（3）the number of settlement distribution,the number of new settlement points are negatively correlated with the distribution of geological hazard hidden danger points.（4）in each statistical year,the distribution,new number and aggregation degree of settlement points increase with the increase of peak acceleration g.From the point of view of topography and geomorphology:（1）the number and new number of rural settlement points gradually decrease with the increase of relative height difference,and are mainly distributed in the relative height difference areas of 0-18 m,18-36 m and36-57m;（2）in each annual section,the buffer zone which is not affected by the slope direction of the fault zone is higher than that affected by the south-east slope direction of the fault zone.（3）the distribution,new quantity and point density of settlement points are mainly concentrated in the geomorphology area of eroded mountain deep cutting canyon and the middle alpine canyon area of tectonic denudation,and the proportion of other Quaternary main geomorphological areas is very small.（4）the distribution and new number of settlement sites increase with the increase of dangerous geomorphology.Comparing the historical maximum intensity and Ludian seismic fortification intensity,we can see that when it is higher than the seismic fortification,the degree of aggregation decreases with the maximum degree of dangerous geomorphology,and vice versa.3.From the point of view of stratigraphic geology:（1）in the distribution area of soft rock and semi-hard to hard rock group of engineering rock group,the distribution of settlement points,the number of new settlement points and the degree of accumulation are the largest.（2）in terms of settlement distribution and new quantity,it is mainly concentrated in the areas of quartz sand,fine sand and muddy silt and miscellaneous sand,while in terms of the degree of aggregation,it is mainly concentrated in the areas of quartz sand,fine sand and clay,and the areas without soil with the highest hardness are the lowest.（3）the distribution of settlement points and the number of new settlement points are higher according to the higher the degree of rock fragmentation,that is,the lower the degree of rock fragmentation,the higher the proportion of the number of settlement points and new settlement points.（4）Water carrying capacity: the distribution of settlement points,the number of new settlement points and the arrangement of point density from large to small（except for the interval from 1642 to 1750）are as follows: karst water area > fissure water area > pore water area.（5）the settlement distribution and new settlement points are mainly concentrated in the rock layer thickness of 0-200 m and the rock layer thickness of 400-600 m,and the degree of accumulation in these two areas is also large.On the other hand,it is discussed that residents are still more likely to choose areas with poor safety when choosing settlement sites,and the problems exposed are as follows: 1.Drinking water problem: often choose the area close to the river,the groundwater is the karst water area,the soil quality of the site is poor,it is convenient to obtain water resources through river water intake or drilling;2.Farming problems:often choose to erode the mountain and cut the canyon geomorphology area,easy to obtain the valley and close to the water source,convenient for farming;3.Construction technology problems: often choose areas with poor rock type and poor soil type to facilitate building foundation and soil wall construction.