Geological Environment Quality Evaluation Of The Most Severely-afflicted Seismic Area In Mesopotamia Of Pengzhou City

The May 12,2008 Wenchuan M=8.0 earthquake was the most severe seismic hazard of our country in recent years. The secondary geological hazards triggered by the earthquake, such as the landslide, the collapse and the debris flow could cause huge casualties and property damages, let alone the geological environment. Baishui river and bailu river basin lie in the northwest of the epicenter, meanwhile, the Yinxiu beichuan fault passed through this area. Thus this area was most severely-afflicted caused by the earthquake. On the other hand, the Mesopotamia was the most important tourism of Pengzhou even Chengdu. In order to accelerate construction after the earthquake, rational develop and protect the geological environment of Mesopotamia, it was of significant meaning to quantitative evaluate the geological environment quality.This paper was based on existing geological environment evaluation of cities, mines, river basins and districts, comprehensively analyzed the key factor of geological environment quality. Therefore, evaluation index and assessment method were confirmed, which discussed the geological environment quality status and evolution law before and after the earthquake, and after the restoration by different level. And this paper was creative to establish assessment method, also brought penalty function into extreme condition, and proposed restoration and reconstruction after disasters in stages. A few acknowledges were achieved as follows:(1) The May 12, Wenchuan earthquake attacked the fragile geological environment zone, and destroyed the mountain at large. The internal and external process agents had speed up change of circumstances. Landform, the earth’s surface, mountain, hydrogeological condition and geological hazard feature were altered variously. The influence might last 5 to 10 years or even much longer.(2) Five first level evaluation factors were filtrated while nineteen second level.The natural environment, geological environment, seismic environment, geologic hazard and human engineering activity were first level factors. The seismic environment could be divided into three second level factors. They were surface diastrophism, fracture scale, and distance from evaluation unit to active fault. This kind of partitioning method was based on regional geological environment feature.(3) The evaluation shows, before the earthquake the dominant geological environment quality of Mesopotamia was level Ⅱ, which accounted for 49.8%, and 3.5% was level Ⅳ. After the earthquake, the dominant geological environment quality was level Ⅲ, which accounted for 46.9%, and level IV accounted for 17.8%. Due to the intense earthquake magnitude, Mesopotamia located in Longmen mountain fault zone was severely affected.(4) The restoration evaluation of typical geological hazards in the Mesopotamia shows the geological environment quality has been improved after the earthquake. Evaluation result has been increased by 3 to 9 points in the unit. Parts of the unit have raised one level, but still could not achieve the quality level before the earthquake.(5) The geological environment of Mesopotamia has been improved greatly by means of restoration. However because of its steep landform, secondary geological hazard, debris especially, might occur under the heavy rainfall and last for a long time. And equilibrium state might attain only been through long-term evolution. Therefore, restoration and reconstruction after disasters must follow evolution law and carry out in stages.