汶川地震小鱼洞地区的地表破裂和同震位移及其机制讨论
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摘要
2008年5月12日在四川西部发生的汶川地震是一次以逆冲运动为主,兼有右旋走滑运动的斜滑型地震,形成了有史以来最长、最复杂的地表破裂之一。其中,很多复杂现象到目前为止还没有得到很好的解释或一致的认识,如小鱼洞地区出现的NW走向的小鱼洞断裂,在小鱼洞以北出现的2条相距11km的平行断裂同时破裂的现象等。通过在小鱼洞地区的详细野外调查,获得了详细的地表破裂分布及同震位移分布,在此基础上对小鱼洞地区地表破裂的机制进行了分析。结果表明,造成上述复杂地表破裂的根本原因是汶川地震的主断层北川-映秀断裂的产状变化,即北川-映秀断裂在小鱼洞以北向NW偏移约3.5km。其破裂机制是:1)北川-映秀断裂的右旋走滑运动在小鱼洞西侧的左阶挤压阶区引起的挤压隆升形成前冲断层,即小鱼洞断裂;2)由于北川-映秀断裂在小鱼洞以北向NW偏移3.5km,导致其断层面倾角变大,逆冲运动引起的断层上盘对下盘的挤压方向变化,结合右旋走滑引起的上盘对下盘的侧向推挤,两者共同作用突破了彭灌断裂,从而形成了2条相距11km的平行断裂同时错动的现象。另外,文中建议应该重视北川-映秀断裂右旋走滑运动分量、断层产状变化以及断层上、下盘的岩性差异对汶川地震地表破裂过程及地表破裂分布的影响。
The MW 7. 9 Wenchuan,China,earthquake is a large oblique reverse slip shock,whose main fault is dominated by reverse slip with right-lateral strike-slip component. It generated one of the longest and most complicated surface ruptures,and to many of the phenomena,we haven't had an appropriate interpretation or a common understanding,e. g. on the 7km-long NW-trending Xiaoyudong Fault and the coinstantaneous fracture on the two parallel thrust faults which are 11km apart on the north of Xiaoyudong area. Field investigation in the Xiaoyudong area shows clear co-seismic rupture and displacement,and on these bases,we analyzed the mechanism of the surface rupture in the Xiaoyudong area. Our study indicates that the change of attitude of Beichuan-Yingxiu Fault( BYF) , that is,the ca. 3. 5km step-over in the west of the Xiaoyudong area,is the primary cause of the above complex phenomena. Specific mechanisms are as follows: 1 ) The dextral strike-slip of the BYF results in compressional uplift in the left-restraining step-over,creating a frontal reverse fault,known as the Xiaoyudong Fault.; 2) The Pengguan Fault,which is parallel to and 11km apart from the BYF,is activated in the north of the step-over by a combination of the increased dip angle in the north of the step-over due to the ca. 3. 5km left step of the BYF and the lateral push of the hanging wall to the footwall of the BYF caused by the dextral strike-slip of the BYF. These results are helpful in deepening our understanding of the dynamic processes that produced surface ruptures during the Wenchuan earthquake. We also suggest that more attention shall be paid to the impact of the dextral strike-slip component,the change of primary fault's attitude and the difference of the rocks of the fault's two walls on the process and distribution of surface rupture.
The MW 7. 9 Wenchuan,China,earthquake is a large oblique reverse slip shock,whose main fault is dominated by reverse slip with right-lateral strike-slip component. It generated one of the longest and most complicated surface ruptures,and to many of the phenomena,we haven't had an appropriate interpretation or a common understanding,e. g. on the 7km-long NW-trending Xiaoyudong Fault and the coinstantaneous fracture on the two parallel thrust faults which are 11km apart on the north of Xiaoyudong area. Field investigation in the Xiaoyudong area shows clear co-seismic rupture and displacement,and on these bases,we analyzed the mechanism of the surface rupture in the Xiaoyudong area. Our study indicates that the change of attitude of Beichuan-Yingxiu Fault( BYF) , that is,the ca. 3. 5km step-over in the west of the Xiaoyudong area,is the primary cause of the above complex phenomena. Specific mechanisms are as follows: 1 ) The dextral strike-slip of the BYF results in compressional uplift in the left-restraining step-over,creating a frontal reverse fault,known as the Xiaoyudong Fault.; 2) The Pengguan Fault,which is parallel to and 11km apart from the BYF,is activated in the north of the step-over by a combination of the increased dip angle in the north of the step-over due to the ca. 3. 5km left step of the BYF and the lateral push of the hanging wall to the footwall of the BYF caused by the dextral strike-slip of the BYF. These results are helpful in deepening our understanding of the dynamic processes that produced surface ruptures during the Wenchuan earthquake. We also suggest that more attention shall be paid to the impact of the dextral strike-slip component,the change of primary fault's attitude and the difference of the rocks of the fault's two walls on the process and distribution of surface rupture.
引文
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何宏林,孙昭民,王世元,等.2008.汶川MS8.0地震地表破裂带[J].地震地质,30(2):359—362(in Chinese).HE Hong-lin,SUN Zhao-min,WANG Shi-yuan,et al.2008.Rupture of the MS8.0Wenchuan earthquake[J].Seismology and Geology,30(2):359—362(in Chinese).
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刘静,张智慧,文力,等.2008.汶川8级大地震同震破裂的特殊性及构造意义:多条平行破裂同时活动的反序型逆冲地震事件[J].地质学报,82(12):1707—1722.LIU Jing,ZHANG Zhi-hui,WEN Li,et al.2008.The MS8.0Wenchuan earthquake co-seismic rupture and its tectonicimplications—An out-of-sequence thrusting event with slip partitioned on multiple faults[J].Acta GeologicaSinica,82(12):1707—1722(in Chinese).
徐锡伟,陈桂华,于贵华,等.2010.5·12汶川地震地表破裂基本参数的再论证及其构造内涵分析[J].地球物理学报,53(10):2321—2336.XU Xi-wei,CHEN Gui-hua,YU Gui-hua,et al.2010.Reevaluation of surface rupture parameters of the5·12Wenchuanearthquake and its tectonic implication for Tibetan uplift[J].Chinese Journal of Geophysics,53(10):2321—2336(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.The MS8.0Wenchuan earthquake surface ruptures and itsseismogenic structure[J].Seismology and Geology,30(3):594—629(in Chinese).
王卫民,赵连锋,李娟,等,2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of the M8.0Wenchuan earthquake ofSichuan,China[J].Chinese Journal of Geophysics,51(5):1403—1410(in Chinese).
Bayarsayhan C,Bayasgalan A,Enhtuvshin B,et al.1996.1957Gobi-Altay,Mongolia,earthquake as a prototype forsouthern California's most devastating earthquake[J].Geology,24:579—582.
Bowman D,King G,Tapponnier P.2003.Slip partitioning by elastoplastic propagation of oblique slip at depth[J].Science,300:1121—1123.
Dong S W,Zhang Y Q,Wu Z H,et al.2008.Surface rupture and co-seismic displacement produced by the MS8.0Wenchuan earthquake of May12th,2008,Sichuan,China:Eastwards growth of the Qinghai-Tibet plateau[J].Acta Geologica Sinica(English Edition),82(5):938—948.
Fu B,Shi P,Guo H,et al.2011.Surface deformation related to the2008Wenchuan earthquake,and mountain buildingof the Longmenshan,eastern Tibetan plateau[J].Journal of Asian Earth Sciences,40:805—824.
King G,Klinger Y,Bowman D,et al.2005.Slip-partitioned surface breaks for the MW7.82001Kokoxili earthquake,China[J].Bulletin of the Seismological Society of America,95:731—738.
Klinger Y,Xu X,Tapponnier P,et al.2005.High-resolution satellite imagery mapping of the surface rupture and slipdistribution of the MW7.8,November14,2001Kokoxili earthquake(Kunlun Fault,Northern Tibet,China)[J].Bulletin of the Seismological Society of America,95(5):1970—1987.
Lin A,Ren Z K,Jia D,et al.2009.Co-seismic thrusting rupture and slip distribution produced by the2008MW7.9Wenchuan earthquake,China[J].Tectonophysics,471:203—215.
Liu-Zeng J,Zhang Z,Wen L,et al.2009.Co-seismic ruptures of the12May2008,MS8.0Wenchuan earthquake,Sichuan:East-west crustal shortening on oblique,parallel thrusts along the eastern edge of Tibet[J].Earth andPlanet Science Letters,286:355—370.
Liu-Zeng Jing,Li Wen,Jing Sun,et al.2010.Surficial slip and rupture geometry on the Beichuan Fault near Hongkouduring the Mw7.9Wenchuan earthquake,China[J].Bulletin of the Seismological Society of America,100(5B):2615—2650.
Michael A J.1990.Energy constraints on kinematic models of oblique faulting:Loma Prieta versus Parkfield-Coalinga[J].Geophysics Research Letters,17:1453—1456.
Ran Y K,Chen L C,Chen J,et al.2010.Paleoseismic evidence and repeat time of large earthquake at three sites alongthe Longmenshan Fault zone[J].Tectonophysics,491:141—153.
Xu X W,Wen X Z,Yu G H,et al.2009a.Co-seismic reverse-and oblique-slip surface faulting generated by the2008MW7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.
Xu X W,Yu G H,Chen G H,et al.2009b.Parameters of coseismic reverse-and oblique-slip surface ruptures of the2008Wenchuan earthquake,eastern Tibetan plateau[J].Acta Geologica Sinica(English Edition),(4):673—684.
Yu G H,Xu X W,Klinger Y,et al.2010.Fault-scarp features and cascading-rupture model for the Wenchuanearthquake(MW7.9),eastern Tibetan plateau,China[J].Bulletin of the Seismological Society of America,100(5B):2590—2614.
Yuan R M,Xu X W,Chen G H,et al.2010.Ejection landslide at northern terminus of Beichuan rupture triggered by the2008MW7.9Wenchuan earthquake[J].Bulletin of the Seismological Society of America,100(5B):2689—2699.
陈桂华,徐锡伟,郑荣章,等.2008.2008年汶川MS8.0地震地表破裂变形定量分析:北川-映秀断裂地表破裂带[J].地震地质,30(3):723—738.CHEN Gui-hua,XU Xi-wei,ZHENG Rong-zhang,et al.2008.Quantitative analysis of the co-seismic surface rupture ofthe2008Wenchuan earthquake,Sichuan,China,along the Beichuan-Yingxiu Fault[J].Seismology and Geology,30(3):723—738(in Chinese).
付碧宏,时丕龙,张之武.2008.四川汶川MS8.0大地震地表破裂带的遥感影像解析[J].地质学报,82(12):1679—1687.FU Bi-hong,SHI Pi-long,ZHANG Zhi-wu.2008.Spatial characteristics of the surface rupture produced by the MS8.0Wenchuan earthquake using high-resolution remote sensing imagery[J].Acta Geologica Sinica,82(12):1679—1687(in Chinese).
国家重大科学工程“中国地壳运动观测网络”项目组.2008.GPS测定的2008年汶川MS8.0级地震的同震位移场[J].中国科学(D辑),38(10):1195—1206.Research Group of Crustal Movement Observation Network of China.2008.The co-seismic displacement field of the2008MS8.0Wenchuan earthquake measured by GPS[J].Science in China(Ser D),38(10):1195—1206(inChinese).
何宏林,孙昭民,王世元,等.2008.汶川MS8.0地震地表破裂带[J].地震地质,30(2):359—362(in Chinese).HE Hong-lin,SUN Zhao-min,WANG Shi-yuan,et al.2008.Rupture of the MS8.0Wenchuan earthquake[J].Seismology and Geology,30(2):359—362(in Chinese).
李勇,黄润秋,Densmore A L,等.2009.龙门山小鱼洞断裂在汶川地震中的地表破裂及地质意义[J].第四纪研究,29(3):502—512.LI Yong,HUANG Run-qiu,Densmore A L,et al.2009.Surface rupture of Xiaoyudong Fault caused by Wenchuanearthquake and its geological significance[J].Quaternary Sciences,29(3):502—512(in Chinese).
刘静,张智慧,文力,等.2008.汶川8级大地震同震破裂的特殊性及构造意义:多条平行破裂同时活动的反序型逆冲地震事件[J].地质学报,82(12):1707—1722.LIU Jing,ZHANG Zhi-hui,WEN Li,et al.2008.The MS8.0Wenchuan earthquake co-seismic rupture and its tectonicimplications—An out-of-sequence thrusting event with slip partitioned on multiple faults[J].Acta GeologicaSinica,82(12):1707—1722(in Chinese).
徐锡伟,陈桂华,于贵华,等.2010.5·12汶川地震地表破裂基本参数的再论证及其构造内涵分析[J].地球物理学报,53(10):2321—2336.XU Xi-wei,CHEN Gui-hua,YU Gui-hua,et al.2010.Reevaluation of surface rupture parameters of the5·12Wenchuanearthquake and its tectonic implication for Tibetan uplift[J].Chinese Journal of Geophysics,53(10):2321—2336(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.The MS8.0Wenchuan earthquake surface ruptures and itsseismogenic structure[J].Seismology and Geology,30(3):594—629(in Chinese).
王卫民,赵连锋,李娟,等,2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of the M8.0Wenchuan earthquake ofSichuan,China[J].Chinese Journal of Geophysics,51(5):1403—1410(in Chinese).
Bayarsayhan C,Bayasgalan A,Enhtuvshin B,et al.1996.1957Gobi-Altay,Mongolia,earthquake as a prototype forsouthern California's most devastating earthquake[J].Geology,24:579—582.
Bowman D,King G,Tapponnier P.2003.Slip partitioning by elastoplastic propagation of oblique slip at depth[J].Science,300:1121—1123.
Dong S W,Zhang Y Q,Wu Z H,et al.2008.Surface rupture and co-seismic displacement produced by the MS8.0Wenchuan earthquake of May12th,2008,Sichuan,China:Eastwards growth of the Qinghai-Tibet plateau[J].Acta Geologica Sinica(English Edition),82(5):938—948.
Fu B,Shi P,Guo H,et al.2011.Surface deformation related to the2008Wenchuan earthquake,and mountain buildingof the Longmenshan,eastern Tibetan plateau[J].Journal of Asian Earth Sciences,40:805—824.
King G,Klinger Y,Bowman D,et al.2005.Slip-partitioned surface breaks for the MW7.82001Kokoxili earthquake,China[J].Bulletin of the Seismological Society of America,95:731—738.
Klinger Y,Xu X,Tapponnier P,et al.2005.High-resolution satellite imagery mapping of the surface rupture and slipdistribution of the MW7.8,November14,2001Kokoxili earthquake(Kunlun Fault,Northern Tibet,China)[J].Bulletin of the Seismological Society of America,95(5):1970—1987.
Lin A,Ren Z K,Jia D,et al.2009.Co-seismic thrusting rupture and slip distribution produced by the2008MW7.9Wenchuan earthquake,China[J].Tectonophysics,471:203—215.
Liu-Zeng J,Zhang Z,Wen L,et al.2009.Co-seismic ruptures of the12May2008,MS8.0Wenchuan earthquake,Sichuan:East-west crustal shortening on oblique,parallel thrusts along the eastern edge of Tibet[J].Earth andPlanet Science Letters,286:355—370.
Liu-Zeng Jing,Li Wen,Jing Sun,et al.2010.Surficial slip and rupture geometry on the Beichuan Fault near Hongkouduring the Mw7.9Wenchuan earthquake,China[J].Bulletin of the Seismological Society of America,100(5B):2615—2650.
Michael A J.1990.Energy constraints on kinematic models of oblique faulting:Loma Prieta versus Parkfield-Coalinga[J].Geophysics Research Letters,17:1453—1456.
Ran Y K,Chen L C,Chen J,et al.2010.Paleoseismic evidence and repeat time of large earthquake at three sites alongthe Longmenshan Fault zone[J].Tectonophysics,491:141—153.
Xu X W,Wen X Z,Yu G H,et al.2009a.Co-seismic reverse-and oblique-slip surface faulting generated by the2008MW7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.
Xu X W,Yu G H,Chen G H,et al.2009b.Parameters of coseismic reverse-and oblique-slip surface ruptures of the2008Wenchuan earthquake,eastern Tibetan plateau[J].Acta Geologica Sinica(English Edition),(4):673—684.
Yu G H,Xu X W,Klinger Y,et al.2010.Fault-scarp features and cascading-rupture model for the Wenchuanearthquake(MW7.9),eastern Tibetan plateau,China[J].Bulletin of the Seismological Society of America,100(5B):2590—2614.
Yuan R M,Xu X W,Chen G H,et al.2010.Ejection landslide at northern terminus of Beichuan rupture triggered by the2008MW7.9Wenchuan earthquake[J].Bulletin of the Seismological Society of America,100(5B):2689—2699.
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