【摘要】 文章以龙门山中央断裂带映秀-北川断裂带为研究对象,重点对汶川地震破裂带南段虹口乡八角庙地区地表断裂带进行了详细研究,并结合汶川地震科学钻探1号孔(WFSD-1)岩芯部分研究成果,探讨龙门山中央断裂带的物质组成及其结构特征。研究表明,映秀-北川断裂带由很多次级小规模断裂(破碎带)以及夹持其中的块体所构成,其中断层泥的厚度由几毫米到25cm不等,与WFSD-1岩芯记录的地震断裂现象基本一致。从虹口乡八角庙露头来看,映秀-北川断裂带整体宽约120m,分布有近80条含有断层泥的次级断裂带。以台湾车笼埔断裂钻探项目(TCDP)和汶川地震科学钻探(WFSD)研究来看,一次大地震只能形成几毫米至约2cm厚的断层泥,推断映秀-北川断裂带中每层断层泥至少发生过1次到13次地震,该区总厚度约150cm的断层泥中发生地震次数至少为183次,说明沿着映秀-北川断裂带重复发生过多次强地震活动。每次地震活动并不完全沿袭老的地震断裂主滑移带滑动,而是沿着断层泥边部区域滑动。从整个断裂带中断层泥分布特征来看,地震断裂活动具有向断裂下盘迁移的趋势,并且断层泥的厚度与断裂活动性成正比关系,表明断裂带宽度与地震活动次数及其演化历史有着成因上的直接联系,多次地震活动叠加可能是龙门山形成的主要成因。更多还原

【Abstract】 This paper focuses on the research of the Yingxiu-Beichuan fault zone,which is the central fault of Longmuanshan fault belt.Detailed study was taken on the fault zone in Bajiaomiao village,Hongkou town at the coseismic surface rupture zone of Wenchuan earthquake.Combining with analyses of the drilling cores from the No.1 Well of the Wenchuan Earthquake Fault Scientific Drilling(WFSD-1)Project,the composition features and structure of the Longmenshan fault belt was discussed.Our research indicates that Yingxiu-Beichuan fault zone is composed by many small sub-faults(damage zone).The thickness of the gouge in the fault zone ranges from several millimeters to 25 centimeters,which is consistent with the fault characters recorded in the drilling cores of the WFSD-1.The width of Yingxiu-Beichuan fault zone is about 120m viewed from the outcrops in Bajiaomiao village.More than 80 small subfaults that contain gouge distributed in this area.Only several millimeters to approximately 2 centimeters gouge can be formed from the experiences in Taiwan Chelungpu-fault Drilling Project(TCDP)and Wenchuan Earthquake Fault Scientific Drilling(WFSD)Project,so we can infer that each layer of the gouge in Yingxiu-Beichuan fault zone might be produced by 1 to 13 large earthquakes at least.The total thickness of the gouge in this area is about 150cm,which indicates at least 183 earthquake events and suggests that strong earthquake repeatedly occurred along the Yingxiu-Beichuan fault zone.Each earthquake does not completely slip along the principal slip zone(PSZ)of the older earthquake,but rather along the edge of the gouge.According to the gouge statistics of the whole fault zone,seismic events have the obvious tendency towards the foot wall,and the thickness of gouge is proportional to the activity of the fault,indicating that the width of fault zone has the directly relation with the number of times and evolution history of earthquake event.Repeated earthquakes maybe the main cause of formation of Longmenshan Moutain.更多还原