四川龙门山安县-灌县断裂带的特征——以汶川地震断裂带科学钻探3号孔(WFSD-3)岩心为例

汶川地震断裂带科学钻探(WFSD)是由科技部、国土资源部和中国地震局联合组织实施的汶川地震断裂带科学钻探研究项目,计划在同震地表破裂带(龙门山映秀-北川断裂和安县-灌县断裂)的上盘布置5口科学群钻:WFSD-1、WFSD-2、WFSD-3、WFSD-3P和WFSD-4,其中WFSD-3和WFSD-3P位于龙门山前山断裂安县-灌县断裂的上盘。以WFSD-3钻孔岩心为研究对象,进行详细的岩石学、构造学、野外编录等研究。WFSD-3钻孔岩心中的断裂岩主要由断层角砾岩、碎裂岩和断层泥组成,未见假玄武玻璃。钻孔中存在26条规模不等的断裂带,断裂密度显示FZ634、FZ1215和FZ1250为主要断裂带,而FZ1250可能为2008年汶川地震的主滑移带。安县-灌县断裂在地表和WFSD-3P、WFSD-3钻孔岩心中的断层倾角分别约为60°、46°和38°,显示安县-灌县断裂倾角从地表至深部逐渐变缓,为一铲式逆冲断层。

Features of the Anxian - Guanxian fault zone in Longmenshan area of Sichuan Province: A case study of No. 3 hole of Wenchuan Earthquake Fault Zone Scientific Drilling (WFSD-3)

Wenchuan Earthquake Fault Zone Scientific Drilling (WFSD) was organized jointly by Ministry of Science and Technology, Ministry of Land and Resources and China Bureau of Seismology. The WFSD project plans to drill five scientific wells on the hanging wall of the co-seismic surface rupture zone, including the Yingxiu-Beichuan fault and the Anxian-Guanxian fault in Longmenshan area. The five drilling holes include WFSD-1, WFSD-2, WFSD-3, WFSD-3P and WFSD-4. The WFSD-3 and WFSD-3P drill holes are located on the hanging wall of the Anxian-Guanxian fault. Basic studies were carried out for the WFSD-3 drilling cores in such aspects as petrology, structural geology and borehole logging. The results show that the fault-rocks in the WFSF-3 contain fault breccia, cataclastic rock and fault gouge. The pseudotachylite does not appear in this well. Twenty-six fault zones were detected in this well, including the three main major fault zones of FZ634, FZ1215 and FZ1250, with the FZ1250 being the possible primary slip zone during the 2008 Wenchuan earthquake. The dip angles of the trench, WFSD-3P and WFSD-3 are respectively about 60°, 46° and 38°. The variation of the dip angle indicates that the Anxian-Guanxian fault is a listric thrust fault with low dip angle.