| Wenchuan has happened the Richter scale 8.0 and magnitude scale 7.9 earthquakes, which caused serious casualties and property loss and it was the most earthquake disaster affecting the widest range, since the founding of new China. The result of this great disaster is that more than 87150 people died and a large number of houses and infrastructures were damaged, industrial and agricultural production has been suffered a heavy loss, the ecological environment has been severely damaged, with direct economic losses of RMB 845.1 billion Yuan.The number and scale of the avalanches landslides, mudslides and dammed lake,etc secondary geological disasters were immense. On the basis of the preliminary results in"5.12"Wenchuan earthquake, the earthquake area has increased more than 5 000 geologic hazards,the strains of which the familiar four geologic hazards take up more than 97 percents,are landslide ,debris flow ,callapse and unstable slope.The investigation date of 44 serious damaged countries show that the earthquake area developed more than 872 potential debris flow gullies ,among them,90 potential debris flow gullies belong to super-huge magnitude 91 huge magnitude,300middle magnitude and 355 little magnitude.The survey result come from Chinese Ministry of Land and Resources shows that,there are more than 24 country-level cities and 100 towns or villages was endangered by those potential debris flow.Wenchuan Beichuan and Mianzhu etc.of the strong damaged areas occurred regional debris flow on 24, September 2008,only 4 months after"5.12"Wenchuan earthquake,which caused more than 40 people dead and missed,the thousands and hundreds acres fertile lands and houses were bueied and damaged,and the disaster of the scale and destructive power is so strong that the other of the disasters are incomparable.Some areas of Sichuan province have rained enormously on 12～14,August 2010,less than two years after―9.24‖debris flow, so that the strong damaged areas occurred the critical debris flow again, which include Qingping village Mianzhu, Yingxiu town Wenchuan and Longchi town Dujiangyan. The two debris flows show that the earthquake areas have entered a new active time, in the next certain time, the areas will occur the debris flow more frequently.The paper analyes the distribution features of debris flow after the earthquake and the changes of the source, stimulating rainfall, activity in the west of SiChuan areas (especially near the fault zone).And take the Zoumaling debris flow after the earthquake as an example, it demonstratesthe features with that the amount of source will increas, stimulating rainfall will reduce and activities will enhance in ditch region after the earthquake. At the same time, with rain spread method back caculate the stimulating rainfall if the ditch happen the debris flow between the earthquake as the same scale as after, and with the appropriate modified Liu Xilin - Tang Chuan model to predict the frequency laid down in different Maling risk of debris flow accumulation body Range, then explained that the activity of the earthquake Zoumaling debris is greatly enhanced.On the basis of the analysis, this paper gets several points about the main cognition and the conclusion of the Zoumaling flow:(1) It is a new flow after the Wenchuan earthquake. It is located in the Yinxing scenic Mianzhu, and is the best palace for the summer before the earthquake. From the first rainy season after the earthquake, it began to break out the―9.24" flow, and then the Zoumaling flow went into the active time. So it is a representative debris flow caused by the earthquake.(2) The debris flow is bound up with the geologic structure and the characteristic stratum of the Zoumaling. If the earthquake was the blasting fuse of the flow, its geologic structure and the characteristic stratum was the essential element to bring out the flow. There is the Longmen mountain center fracture (Yingxiu-Beichuan fracture) to go across in the Zoumaling. And it was the center fracture that brings out the Wenchuan earthquake as the main fracture. Moreover, the main trench Zoumaling Cambrian stone under the head of systems Qingping mica and quartz sandstone shale, carbonaceous shale, weathered surface, soft rock crushing. Under earthquake they are prone to loosen as the source of debris flow.(3) Compared with the general source area replenishment, it is different from the general flow. The source mainly include three varieties: the collapse and landslide kind, the erosion of the slope kind, the accumulation kind, and the energy of them are supplied by the earthquake. Within the current channel may be involved in Zoumaling loose debris flow source of total solids 432.66×104m3, 50 year return frequency storm debris flow activity may be involved in the dynamic reserves of 121.06×104m3. In the certain time of future, the source will become a essential condition for debris flow.(4) Combined with the forecast range of debris flow risk (the results shown in Table 5-3 and Figure 5-8 to 5-12) and the inversion of rainfall, and before the earthquake to stimulating rainfall is 114.72mm / h, and after the earthquake to stimulate rainfall was 70mm / h (showing Table 5-8). We can conclude that, Zoumaling ditch stimulate rainfall greatly reduced, and the risk range also has increased with the rainfall frequency vary.(5) Through researching the prediction of dangerous areas and calculation the rainfall before the earthquake in Zoumaling, this paper demonstrates the impact between the earthquake and seismic source, rainfall, stimulate activity. And then also explains that Zoumaling debris flow is on development stage. In the next certain time, the activity of debris flow will be very frequent, and the debris flow activity will be stable, until the deposits both sides of the trench and bank on the slope is stable. |
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