Analysis and evaluation of geohazard intensity of the Wenchuan earthquake, Sichuan

In order to study the evaluation method and index system of regional group-occurring geohazard activities, take for example the evaluation of the intensity of geohazard activity induced by the Wenchuan earthquake, the authors calculated the maximum surface density of distribution of geohazards induced by the Wenchuan earthquake on the basis of a simple analysis of the macroscopic features of geohazards induced by the earthquake and by using high-precision remote sensing interpretation data and GIS data. In addition, in combination with the recent analysis of historic data got by geohazard survey of Baoji City, Shaanxi, the authors proposed the basic idea of taking the maximum surface density of geohazard distribution as the indices of the intensity of regional geohazard activity and classification standard. Eight classes of the indices of the intensity of geohazard activity were preliminarily established, of which the highest intensity of geohazard activity induced by the Wenchuan earthquake is class 7, belonging to extremely strong activity. The area with the strongest geohazard activity (class 7 activity area) is located on both sides of the causative earthquake on both banks of the Minjiang River near Yingxiu Township and in the upper reaches of the Yinchang Gully, Hanwang Township, Mianzhu in the epicenter area of the strong earthquake. The area with the less strong geohazard activity (class 6 activity area) is situated on both bank of the Qianhe River in the seat of Beichuan County and on both banks of a small river northeast of Nanba Township, Pingwu County. It is revealed that the activity intensity of geohazards had a trend of significant decline from the causative fault zone toward both sides. Finally, the paper briefly discusses the main cause for so strong geohazard activities deduced by the Wenchuan earthquake and their development trend.