Earthquake Risk Assessment On The Southeast Section Of Bolhinur Fault

The Bolhinur-Aqikekuduke Fault cuts Tian Shan Mountain obliquely, is an active fault belt in large scale. This fault stretches along southeast direction from the southwest bank of Allah Lake Kazakhstan to southwestern margin of Turpan Basin and extends over 1000 km. Within the territory of China, The Bolhinur-Aqikekuduke Fault extends over 860 km, and most section of The Bolhinur-Aqikekuduke Fault are located at no man’s land of mountain and activity area of modern glacial. The fault belt generally headed northwest direction. Research shows, this fault is still active in the Holocene.According to some former works, this paper based on a great deal of field geological survey at the southeast section of the Bolhinur Fault and drew a conclusion of tectonic deformation characteristics, active slip rate of the southeast section of the Bolhinur Fault. In the process of field geological survey, large trench excavation and digital elevation model(DEM) establishment are used to get seismicity parameters of the fault. Data collected from field geological surveys indicate that T1 terrace has vertical cut for about 4.6m, T2 terrace has vertical cut for 11.2m, largest angle of reverse scarp is 27°, indicates that the reverse fault has some activities since Pleistocene. Combined with the dating data, the author has calculated the vertical slop rate of T1 terrace is 0.6mm/a and 0.93mm/a as to T2 terrace. According to the assumed geological section, we find the shortening rate of T3 terrace is 37.34 m, and the shortening rate of T3 terrace is 1.07mm/a.Through the correction of activity data, ancient seismic method and so on, the research indicates the average magnitude if history in the southeast section of the Bolhinur Fault is 7.3, and the maximum magnitude of potential earthquake is 7.5. The method of ancient seismic shows in this area there were at least 3 times of big earthquake has happened, the average earthquake recurrence period is 6~7ka. Last but not least, the probability of earthquake in the southeast section of the Bolhinur Fault within 50 years and 200 years is 0.3%~0.4% and 2%~3% separately.