The Activity Of Litang-Yajiang Block And The Stability Evaluation Of Projects

Yalongjiang Lianghekou and Yageng hydropower station which is being programmed locates in the valley plot of middle and up river in Yalongjiang in Sichuan province Yajiang County. And they are in the centre belt of the Litang—Yajiang block. Further study of the character and activity of the block and evaluate regional structural stability have great significance for the programmed hydropower stations and the large projects.On the base of a great deal of the geological survey, this paper has dissected the structural character and activity of the block and evaluated the suitability of the project. We supplied major geology reference material for the project program by through a series of new way, new technology, new method, such as neotectonics, activity structure, measure age of fault, and combine seismogeology, geophysics, remote sensing technology.Litang—Yajiang block locates in the interior of west Sichuan plateau region and belongs to a part of Sichuan-Yunnan block. Having been surrounding by Xianshuihe fault, Yulongxi fault, Litang-Dewu fault and Ganzi fault, there are three secondary blocks neighbored—Longmenshan block, Liangshan block and Chuanxi block.These boundary faults in Litang—Yajiang block have different characters. Many small faults of Xianshuihe fault are arranged in Pinnate and it is deep dissectely about over 10 km into crust. Many research indicate that it trend to left lateral slip, and the movement is many period and inherit. The Yulongxi fault generally is a high angle thrust fault. And we first find the quaternary fault in the fault belt. Litang-Dewu fault is a left slide and twist fault, so did the Ganzi-Litang fault. We use SEM and ESR to test the movement age and find that they have obverse activity in Holocene.The inner of the block have the Songpan-Ganzi orogenic belt, which include Yajiang arc structural belt and the Zhushang arc structural belt. And the fault structure in amount and scale is little and small compared to the edge faults. The main fault is the NW striking fault and the secondary is the NE striking and the SN striking faults. Most of these faults are thrust fault. Analysis of geology and test of SEM and ESR indicate that movement is feebleness in Holocene. The edge of block is the change belt of physical geography character index such as bouguer gravity anomaly, magnetic anomaly, and the change related to structure character of the fault belt. The change belt is fitting the earthquake, which is present line type. Deep structure, remote sensing, surface features can prove that the three faults is the large scale fault belt which is deeply cut crust.The inner block is the area which the Moho surface depth of burial is the deepest and the physical geography character change gently, element and structure of crust lithosphere matter relatively simple.We choose indexes such as geology background condition, activity fault, seismic character and physical geography character to apply the geology analyses and the fuzzy mathemetics and indicate that Litang—Yajiang block is the basic stability area.Yanglongjiang across the Litang—Yajiang block in south north. The lower of the river in Yajiang County is being programmed the Lianghekou and Yageng hydropower engineering. According to the safety island method of Mister Li-siguang, these is also the safe area among the fiercely earthquake areas. The relatively safety area is the block surrounded by the large fault. Analysis and research from field and fuzzy math shows that Litang-Yajiang block is the fundamental steady area. Yalongjiang Lianghekou and Yageng hydropower station has located in the centre of block region. The two stations don't effect by the huge earthquake and induced earthquake, the project area has upper stability. Yageng station stands a rock mass directly, so it has higher stability. Some boundary faults may have definite effect to the project, but as a whole, it was possible to avoid being much affected from their activities. Litang-Yajiang block is suitable for construction of hydropower engineering the large projects.