汶川8级大地震同震破裂的特殊性及构造意义——多条平行断裂同时活动的反序型逆冲地震事件  

The M_S 8.0 Wenchuan Earthquake Co-seismic Rupture and Its Tectonic Implications——An Out-of-sequence Thrusting Event with Slip Partitioned on Multiple Faults

作　　者：刘静[1] 张智慧[1] 文力[1] 孙杰[1] 邢秀臣[1] 胡古月[2] 许强[1] Paul TAPPONNIER 曾令森[2] 丁林[1] 刘延乐 

机构地区：[1]中国科学院青藏高原研究所,北京100085 [2]中国地质科学院地质研究所,北京100037 [3]Laboratoire de Tectonique,Institut de Physique du Globe,parisfrance75005 [4]江苏省赣榆县地震局,江苏赣榆222100

出　　处：《地质学报》2008年第12期1707-1722,共16页Acta Geologica Sinica

基　　金：国家自然科学基金(编号40672141);中国科学院知识创新工程引进国外优秀人才"百人计划";中国科学院院长基金特别项目资助的成果

摘　　要：汶川地震是有仪器记录以来发生的世界上最大的板内逆冲型地震之一。野外调查表明,沿北东走向的龙门山断裂带上,至少有两条逆冲断裂同时参与汶川地震的同震破裂过程,即北川断裂和安县-灌县断裂(彭灌断裂)。倾向北西的高角度北川逆冲断裂上的地表破裂长度大于200km,可能达225km。运动方式在南部表现为以北西盘抬升的逆冲为主,往北东转为逆冲右旋走滑,走滑分量与垂向陡坎高度相当,陡坎高度最大值约为11m。在彭灌断裂上,地表破裂表现为北西盘抬升的近纯逆冲性质的破裂,破裂长度达70km,陡坎最高达3～3.5m。汶川地震是世界上第一次明确记录到多条平行断裂参与同震破裂的逆冲型地震,而且因发震断层是龙门山断裂带内部的高角度逆冲断裂,而非断裂带前锋的低角度逆冲断裂,所以汶川地震属于反序型逆冲断裂活动。这与1999年我国台湾7.5级集集地震和2005年克什米尔7.6级地震类似,说明反序型逆冲地震具有普遍性。汶川地震这一震级大、破裂长的逆冲地震事件是对目前流行的青藏高原下地壳流动的变形假说提出的严峻挑战,同时也表明加强青藏高原东缘南北地震带上其他滑动速率较低但同样具有发生大地震可能性的活动断裂的滑动速率和古地震定量研究的紧迫性,因为这一地区人口密度与东部相当,但发生强震的频率更高。The Ms 8.0 Wenchuan earthquake ranks as one of the world＇s largest intraplate mega-thrust the last 150 years. Field investigation shows clear surface breaks along two thrusts, Beiehuan and An Xian-Guan Xian （Pengguan） faults, of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping high angle Beichuan fault is over 200 km, possibly 225 km long. Slip on this fault is dominantly NW hanging-wall up thrust in the south; to the northeast, it changes to oblique thrust with near equal amounts of thrust and right-lateral components. Maximum scarp height reaches -11 m locally. Basin-ward of this rupture, another continuous surface break is observed for over 70 km on the parallel, shallower-NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of 3-3. 5 m. Wenchuan rupture is one ofthe very few reported instance of coseismic surface rupture on parallel thrusts. Because the co-seismic rupture is partitioned on the high-angle thrusts within the imbricate thrust system, rather than the frontal thrusts, Wenchuan rupture is thus an out-of-sequence thrusting event, similar to the 1999 Chi-chi M 7. 5 and the 2005 Kashmir M 7. 6 earthquakes, suggesting that out-of-sequence thrusting events are more common than previously thought. This long rupture, large-offset, thrusting event calls for a re-evaluation of the lower crustal channel flow models, which anticipate little or no active shortening of the upper crust along that edge of the plateau, and for an urgent quantitative re assessment of slip rates and paleoseismic behavior on other slow-moving yet with potential of large earthquakes, active faults along the densely-populated eastern margin of the Tibetan plateau.

关 键 词：汶川地震 地表破裂带 同震破裂位移分配 反序型逆冲地震事件 下地壳管道流模型 

分 类 号：P315.2[天文地球—地震学]