摘要
汶川M_s8.0地震形成的地表破裂带主要沿松散沉积层分布,但在北川-映秀地表破裂带中,发现5处同震地表破裂带穿过基岩。通过详细介绍其中的4处基岩同震断层剖面,给出基岩同震断层泥的特点和识别标志。断层剖面位置从北向南:平武平溪、北川擂鼓、安县肖家桥和虹口八角庙。同震断层主要出露在相对较软的基岩中,断层长期活动形成了分带性特征显著的断层变形带,主要包括构造角砾岩、断层角砾、老断层泥和最新断层泥。其中,同震滑动产生的最新断层泥最为松软,厚度最薄,颜色最深,内部几乎不含角砾并与其他部分接触边界清晰平直。基岩同震断层泥的结构特征与断层围岩性质密切相关,当同震断层上下盘围岩由多种岩石组成,而且上下盘围岩强度差别较大时,断层变形带结构相对复杂,发育有厚层断层泥,局部存在多个滑动面;当上下盘围岩岩石组成相对单一时,断层变形带结构相对简单,断层泥厚度较薄。在野外断层变形带结构划分基础上,对部分断层剖面中的同震断层泥和断层岩进行了初步的显微结构分析,给出断层蠕滑和粘滑的显微结构特征,对同震断层泥中的流体活动方式进行了讨论。
Surface rupture zones formed by the Wenchuan Ms 8.0 earthquake are mainly in loose sediments,but in the Beichuan-Yingxiu surface rupture zone,five co-sesimic faults are found to cut into bed rocks. In this paper,four of them were studied through observing and analyzing of their fault gouge. These four faults are located from north to south in Pingxi Town of Pingwu County, Leigu Town of Beichuan County, Xiaojiaqiao Town of Anxian County, and Bajiaomiao of Hongkou Town. In these four faults there are breccia, old fault gouges,and new fault gouges. The new fault gouges are different from the old fault gouges. They are dark, very thin, and very fine-grained, and have no rubble. They have sharp and straight contact boundaries with wall rocks. The structures of gouges are strongly dependent on wall rocks. Where rocks across a co-seismic fault are very different in lithology and strength,the fault gouges are thicker and have more complex structures, for example, consisting of many small slip surfaces. Where rocks across a co-seismic fault are similar in lithology,the gouges are thinner and show rather simple structures. The micro-structural characteristics of the gouges were also studied. Fluid flow could play an important role in the formation of co-seismic fault gouges.
出处
《第四纪研究》
CAS
CSCD
北大核心
2010年第4期745-758,共14页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:40972146)
地震动力学国家重点实验室自主课题(批准号:LED2008A03和LED2009A01)
中国地震局地质研究所基本科研业务费(批准号:IGCEA0906)共同资助
