汶川M_w 7.9级地震同震断层陡坎类型与级联破裂模型  

Earthquake fault scarps and cascading-rupture model for the Wenchuan earthquake.

作　　者：于贵华[1] 徐锡伟[1] Yann Klinger 刁桂苓[3] 陈桂华[1] 冯向东[3] 李陈侠[4] 朱艾斓[5] 袁仁茂[1] 郭婷婷[1] 谭锡斌[1] 安艳芬[1] 孙鑫喆[1] 

机构地区：[1]中国地震局地质研究所,国家活动断层研究中心,北京100029 [2]国家科学研究中心地球科学院 [3]河北省地震局,河北石家庄050021 [4]中国地震局兰州地震研究所,甘肃兰州730000 [5]上海地震局,上海200062

出　　处：《地学前缘》2010年第5期1-18,共18页Earth Science Frontiers

基　　金：国家自然科学基金项目(40974057;40821160550)

摘　　要：2008年5月12日,汶川Mw7.9级地震在青藏高原东缘沿龙门山逆冲断裂带中段形成了两条NE向和一条NW向逆冲走滑型地表破裂。依据同震地表陡坎形态特征,将其分为8种类型:逆断层陡坎、上盘垮塌陡坎、挤压推覆陡坎、右旋挤压推覆陡坎、断层相关褶皱陡坎、后冲挤压陡坎、上冲叠覆陡坎和局部正断层陡坎。汶川地震所形成的同震地表破裂主要由以逆冲为主的映秀破裂段和兼具逆冲、右旋走滑的北川破裂段两部分组成,这两个破裂段分别对应于Mw7.8与Mw7.6级地震事件;它们还可进一步细分为分别对应于Mw7.5、Mw7.7、Mw7.0和Mw7.5等4个次级事件的4个次级破裂段。这些次级破裂段的级联破裂可以用来解释为什么汶川地震的持续时间长达110 s。余震震源机制分析结果表明,发震断层的倾角随深度的增加而变缓,且从西南向北东逐渐变陡可以用来解释走滑分量增加的成因。此次大地震还表明,沿青藏高原东缘地形抬高的主要驱动力可能是地壳挤压缩短,而不一定是下地壳物质流动和膨胀引起上地壳的隆升。The 2008 Mw 7.9 Wenchuan earthquake had caused the rupture of two NE-striking imbricated reverse faults and one NW-striking reverse fault along the Longmenshan range,which forms the eastern boundary of the Tibetan Plateau.On the basis of the morphology of the co-seismic fault scarp,we distinguish eight different categories of fault scarps,namely： the simple thrust scarp,the hanging-wall collapse scarp,the simple pressure ridge,the dextral pressure ridge,the fault-related fold scarp,the back-thrust pressure ridge,the local normal fault scarp and the pavement suprathrust scarp.The surface rupture zone can be divided into two parts,the Yingxiu segment and the Beichuan segment.The Yingxiu segment is dominated by reverse deformation with a smaller component of right-lateral motion,and the Beichuan segment is dominated by right oblique-slip faulting with comparable horizontal and vertical motion.These two segments correspond to a Mw 7.8 event and a Mw 7.6 event,respectively.They can in turn be divided into four second-order sub-segments,which are equivalent to four sub-events of Mw 7.5,Mw 7.7,Mw 7.0 and Mw 7.5,respectively.The cascading-rupture can be used to explain why the earthquake lasted for 110 seconds.The analytical results of the aftershock focal mechanism show that the seismogenic fault dip angle is slowing down with depth,and is gradually steepening from southwest to northeast,which could be used to explain the increases of strike-slip component.This major earthquake confirms that upper crustal shortening can produce the high topography of the Longmenshan without calling on other uplift mechanisms.

关 键 词：汶川地震 地震地表破裂带 断层分段 级联破裂 龙门山冲断裂带 青藏高原 

分 类 号：P315.73[天文地球—地震学]