| Since the2008Wenchuan Earthquake, researches on the seismic landslidebecome one of the most popular research topics in the geological engineering field,According to field investigation, there are lots of large-scale seismic landslidesdistributed in groups along the Daduhe River in western China. And16large-scalelandslide accumulations were distributed between Detuo and Huangjinping reach,with the line density of0.25per kilometer, as the reach slope consisted of Proterozoicgranite and diorite. But seismic landslides triggered by Wenchuan Earthquake werealmost developed in layered sedimentary rocks or metamorphic rocks area, and onlysome collapses were developed in the Proterozoic granite and diorite area near theepicenter. What factors determined this huge difference? Dose the seismic landslidehave a direct or indirect impact on the geological environment of the Daduhe River?Many geologists were concerned about these questions. Systematic investigation andanalysis on the characteristics of seismic landslide developed in Daduhe River as wellas revealing its genetic mechanism have theoretical and practical significance. Fundedby the Geological Survey and the National Science Foundation of China, the authoruses the methods such as: high-precision remote sensing interpretation, fieldinvestigation, core-drilling, geophysical, large-scale geological survey, statisticalanalysis, qualitative analysis and numerical simulation, to do research on theevolution of the Daduhe valley, the stress concentration characteristics in this area, thedevelopment characteristics, the distribution feature and the genetic mechanism theseismic landslide. The achievements and conclusions are given as follow.(1) This paper reveals the evolution characteristics of the Daduhe valley for thefirst time. The author did geomorphologic analysis and ESR dating at terraces orplanation surfaces in different reaches of the Daduhe River. Combined with theprevious achievements related to the river’s evolution, the author complemented theevolution research of the whole river. Conclusions are obtained that the Daduhe River is mainly developed with3planation surfaces and4-6terraces, that both the upstreamand the downstream of this river are wide, that the middle stream is narrow and theriver strike is controlled by regional fault structures.(2) This paper summed up six high ground-stress concentration modes in theDaduhe River. The author analyzed the distribution characteristics of highground-stress with support of ground-stress testing data from related projects, andcomprehension of fault activity characteristics. This paper also reveals characteristicsand distribution of the high ground-stress concentration area, which is near XiaojinCounty, Danba County, Jintang District, Luding County, Dagangshan District,Pubugou District and Jinkouhe County. This paper firstly proposed six modes abouthigh ground-stress concentration including Echelon or intersection high ground-stressconcentration mode, ends of trapezoidal fault block high ground-stress concentrationmode, top of arc structure high ground-stress concentration mode, three groupsfracture intersections high ground-stress concentration mode, fracture tightening partshigh ground-stress concentration mode, intersection turning parts of NE-strikefracture and NW-strike fracture high ground-stress concentration mode.(3) The developing regularity of the Daduhe seismic landslides is also revealedin this paper.22landslides on the Daduhe geological zone (most of landslides arestudied in first time) were researched. Through statistical analysis of landslide, it wasconcluded that the landslides are large-scale, high source of slip, long distancemovement and caused river barrage. On the basis of investigation, researching theplan and cross section of serious seismic landslides, and the time of landslidesformation, this paper analyzed three-dimensional relationship and revealed two lawsin plan section (along the river, the fault zone plane distribution law was linear andalong the stress concentration zone was patchy); in cross section, landslides formationin Daduhe valley shoulder, accumulated in river bed and the Micro-topographicalwere special places (such as slope-break thin ridges, isolated hills, cliff and riverconcave bank) where the slope was steep slowly varying and could have the effect ofamplification of seismic waves apparently; on the time scale, the serious landslidescan be divided into two types-old landslides and ancient landslides. Specially, from0to1million and1.5to2.5million years ago, earthquake landslides occur frequently inresearch zone.(4) Deep analysis of Mogangling typical seismic landslide was also made in thispaper. By way of high-precision remote sensing interpretation, core-drilling,geophysical, large-scale geological survey, and ESR dating methods, starting from the geological environmental conditions, this paper analyzed the landslide boundary,composition, and mechanism, reaching the conclusion that the landslide have ejectionand damming characteristics. The high intensity environment, thin ridge topographyand the Detuo fault which pass through the accumulation are beneficial for theformation of landslide. The Mogangling landslide was direct triggered by Moxi7.75earthquake in1786. The genetic mechanism of this landslide is slopeunloading-vibration crack-fault affecting-projectile slip mode.(5) This paper summed up five landslide formation modes triggered byearthquake In Daduhe valley such as the vibration crack planar block slip; vibrationcrack cut slip; vibration crack projectile slip; vibration crack fault affecting projectileslip; vibration crack stage slip etc. |
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