Activity characteristics of faults in the triangle structure area in northern part of Longmenshan in the Shaanxi--Gansu--Sichuan junction

The triangle structure area surrounded by three different strike fault zones in northern part of Longmenshan is one of the important areas associated with earthquake activity in China. This paper studies the activity characteristics and active age of some primary fault zones， such as the southern margin fault zone of Qinling， Pingwu--Qingchuan fault， Minjiang fault and Huya fault. The conclusions are as follows： ① The southern margin fault zone of Qinling is composed of Diebu--Zhouqu fault， Wudu--Kangxian--Lüeyang fault and Chadian--Mianxian fault. The last fault activity was in Late Pleistocene and faults were steady in Holocene. ② Pingwu--Qingchuan fault in northeastern segment of Longmenshan fault zone is a thrust fault with dextral strike-slip component. The last fault activity was in Late Pleistocene and steady in Holocene. ③ Minjiang fault and Huya fault were strongly active from Pleistocene to Holocene. ④ This area is still one of important areas for studying earthquake activity in the future.