Abstract: The Longmenshan Fault zone,trending in NE,lies between the Songpan-Ganzi orogenic belt and the Yangzi block.It consists of four major faults,such as the Houshan Fault,and related thrusting sheets.It is a nappe structure characterized by forward spreading.It formed during the Indo-China movement and was active many times since then.Since the Quaternary,this fault zone has been very active,and exhibits differential activity on its various sections.In this work,we make an integrated analysis of this fault zone based on data of geomorphology,geology,Bouguer gravity anomalies,and earthquakes.The results show that the near NS-striking Leidong Fault,located along Beichuan-Anxian,is the boundary between the middle and northeastern sections of the Longmenshan Fault zone.The two sections have high distinctive activity.The middle section is very active since late Pleistocene time with frequent medium-and small-sized earthquakes,while the northeastern section has weak activity since Quaternary with occasional small earthquakes.Due to the compression and uplift of the Tibetan Plateau and lateral sliding of blocks,the Sichuan-Qinghai block moves towards SEE,resulting in an active boundary of the block.This boundary includes the Mingshan uplift and the middle and southwestern sections of the Longmenshan Fault zone,both of which are truncated by the Mingshan uplift.And the northeastern section of the Longmenshan Fault zone has been abandoned.

Key words: Longmenshan Fault zone, activity segmentation, late-Quaternary

摘要： NE向展布于松潘-甘孜造山带与扬子陆块之间的龙门山断裂带,是由后山断裂等4条主干断裂及其控制的冲断构造岩片组成的具前展式发育特点的推覆构造带。它形成于印支运动,此后多次活动,第四纪以来活动强烈,但不同地段活动程度具有明显的非均一性。根据地貌、地质构造、布格重力异常和地震活动等资料的综合分析研究认为:1)以位于虎牙—北川—安县一线的近SN向虎牙断裂和擂东断裂为界划分出断裂带西南段和东北段,其活动性迥然不同,西南段晚更新世以来活动强烈,中小地震频繁;东北段第四纪活动微弱,仅偶有小震分布。2)在青藏高原被挤压隆升和块体侧向滑移的作用下,川青地块向SEE滑动,使它东缘发育的岷山隆起与被其截切的龙门山断裂带西南段一起构成了川青地块东部的活动边界,而龙门山断裂带东北段则被遗弃。

关键词: 龙门山断裂带, 活动性分段, 晚第四纪