DISTRIBUTION REGULARITY AND DEVELOPMENT CHARACTERISTICS OF GEOHAZARDS IN YUSHU EARTHQUAKE AREA

At 7:49a.m. April 14th 2010,a Ms 7.1 earthquake occurred in Yushu county, Qinghai province, China. The Yushu earthquake not only resulted in destruction of lots of buildings and plenty of casualty, but also brought lots of geo-hazards such as debris flows, rock falls, landslides and ground cracks. So it evidently changed the distribution regularity and development characteristics of the geohazards at the region. Based on field investigations and statistics, the distribution regularity and development characteristics of the geohazards before and after the earthquake are analyzed. The results show that the geohazards scatter in the area and take place from May to July every year. The main types of the geohazards were debris flows and unstable slopes, as well as the main small scale of geohazards before the Yushu earthquake; After the earthquake, the numbers of geohazards increased obviously, and the distribution of geohazards concentrated in the areas where the main faults cross the Valley of Baqu river, the mountain areas of northern Jiegu town and southern of Zhaqu river, and the geohazards distribute sporadically in the areas where far away from the main faults or macroscopic epicenter. The geohazards are controlled evidently not only by the main faults, but also by the shape, altitude and gradient of slopes. The geohazards mainly distributed in the area of within 2km away from north of the main faults, and on the bulgy shape slopes, altitude of 3800～4000m, and the gradient of 25～40,focused on the gradient of 30～35.The geohazards induced by the ground cracks in the mountains develop distinctly, and the numbers of large and middle scales of geohazards increase clearly, so that the harm of geohazards increase greatly. Especially, the geohazards took place more frequently in rain season, which accelerates the development of geohazards in freezing and thawing periods.