ANALYSIS OF INTENSITY AND REGULARITY OF GEOHAZARDS IN UPPER REACHES OF MINJIANG RIVER

The geological environment is complex and fragile in the upper reaches of Minjiang River. Geological hazards mainly landslides, collapses and debris flows in these areas are characterized by large quantity, large scale and serious harm. Especially, many geological hazards were triggered by the Wenchuan Earthquake. This study is based on the geological survey reports before and after the Wenchuan Earthquake, and uses GIS technology and programming computing technology. It makes the point density map, surface density map and volume density map of the upper reaches of Minjiang River with suitable control-points space and searching radius. It is proposed that geohazard intensity can be divided into 8 grades from weak to strong using the point density map, surface density map and volume density map. So, its analysis shows that the geohazard intensity is high in the upper reaches of Minjiang River. The accumulative geohazard intensity before the Wenchuan Earthquake is up to the highest 8^th grade(extremely intense activity). The highest geohazard intensity triggered by Wenchuan Earthquake is the 7^th grade, and most are the 2^th to the 6^th. The main reason of the high cumulative geohazard intensity in the upper reaches of Minjiang River is the frequent occurrence of extreme events such as historical strong earthquake and rainstorms. Generally, the geohazard intensity triggered by the Wenchuan Earthquake is high, and mainly along the Longmen Mountain fault zone and the southern valley area.