芦山地震发震构造及其与汶川地震关系讨论
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摘要
芦山地震发生在巴彦喀拉块体与华南块体之间龙门山推覆构造带南段。野外考察表明,芦山地震在震中区没有形成具有构造地质意义的地震地表破裂带,仅在各山前陡坡地带出现平行于山麓陡坡的张性地裂缝、山地基岩崩塌、滑坡等边坡震动失稳现象和震动引起的砂土液化现象。重新定位的芦山地震余震分布、震源机制解和地表构造地质等分析表明,芦山地震的发震断层为一条现今尚未出露地表、其上断点仍埋藏在地下9km以下地壳中的一条盲逆断层,走向212°,倾向NW,倾角38°±2°,上断点以上至地表的构造变形符合断层扩展背斜模型。根据汶川地震和芦山地震的余震空间分布、地震破裂过程、深浅构造关系等差异反映出它们是分别发生在龙门山推覆构造带中段和南段的两次独立地震破裂事件。
The Lushan earthquake occurred on the southern segment of the Longmenshan thrust belt between the Bayan Har and south China blocks.Field investigations indicated that there is no any earthquake surface rupture zone generated by this earthquake,only secondary surface breaks,such as extensional ground fissures,landslides,bedrock collapses,and liquefactions were found in the epicentral areas,which were caused by slope instability and earthquake vibration.The relocated aftershocks,focal mechanism solutions and surface structural geology further demonstrate that the seismogenic fault of the Lushan earthquake is a blind reverse fault which strikes 212° and dips toward NW with a dip angle of 38°±2°.The upper tip of this blind reverse fault is still at the depth of about 9 km in the upper crust.The structural deformation from above the tip to the ground surface is in accordance with a fault-propagation-anticline model.Besides,the differences in spatial aftershocks' distribution,rupturing process and seismogenic structure suggest that the Wenchuan and Lushan earthquakes are two independent rupturing events occurred along the middle segment and southern segment of the Longmenshan thrust belt,respectively.
The Lushan earthquake occurred on the southern segment of the Longmenshan thrust belt between the Bayan Har and south China blocks.Field investigations indicated that there is no any earthquake surface rupture zone generated by this earthquake,only secondary surface breaks,such as extensional ground fissures,landslides,bedrock collapses,and liquefactions were found in the epicentral areas,which were caused by slope instability and earthquake vibration.The relocated aftershocks,focal mechanism solutions and surface structural geology further demonstrate that the seismogenic fault of the Lushan earthquake is a blind reverse fault which strikes 212° and dips toward NW with a dip angle of 38°±2°.The upper tip of this blind reverse fault is still at the depth of about 9 km in the upper crust.The structural deformation from above the tip to the ground surface is in accordance with a fault-propagation-anticline model.Besides,the differences in spatial aftershocks' distribution,rupturing process and seismogenic structure suggest that the Wenchuan and Lushan earthquakes are two independent rupturing events occurred along the middle segment and southern segment of the Longmenshan thrust belt,respectively.
引文
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[21]谭锡斌,李元希,徐锡伟,等.低温热年代学数据对龙门山逆冲带南段新生代活动性的约束[J].地震地质,2013,35(2)(待刊).
[22]王椿镛,韩渭宾,吴建平,等.松潘-甘孜造山带地壳速度结构[J].地震学报,2003,25(3):229-241.
[23]朱介寿.汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报:自然科学版,2008,35(4):348-356.
[24]刘启元,李昱,陈九辉,等.汶川M S 8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,2009,52(2):309-319.
[25]郭飚,刘启元,陈九辉,等.川西龙门山及邻区地壳上地幔远震P波层析成像[J].地球物理学报,2009,52(2):346-355.
[26]李昱,姚华建,刘启元,等.川西地区台阵环境噪声瑞利波相速度层析成像[J].地球物理学报,2010,53(4):842-852.
[27]Zhang Z,Yuan X,Chen Y,et al.Seismic signature of the collision between the east Tibetan escape flow and the Si-chuan Basin[J].Earth and Planetary Science Letters,2010,292:254-264.
[28]Zhao G,Unsworth M J,Zhan Y,et al.Crustal structure and rheology of the Longmenshan and Wenchuan MW7.9earth-quake epicentral area from magnetotelluric data[J].Geology,2012,40(12):1139-1142.
[29]刘杰,易桂喜,张致伟,等.2013年4月20日四川芦山M7.0级地震介绍[J].地球物理学报,2013,56(4):1004-1407.
[30]曾祥方,罗艳,韩立波,等.2013年4月20日四川芦山M S 7.0地震:一个高角度逆冲地震[J].地球物理学报,2013,56(4):1418-1424.
[31]谢祖军,金笔凯,郑勇,等.近远震波形反演2013年芦山地震震源参数[J].中国科学:D辑,2013,43:1010-1019.
[32]Yeats R S,Sieh K,Allen C R.The Geology of Earthquake[M].Oxford:Oxford University Press,1997:1-568.
[33]Stein R,King G.Seismic potential revealed by surface fold-ing:1983California,earthquake[J].Science,1984,224:869-872.
[34]Stein R,Yeats R S.Hidden earthquakes[J].Scientific American,1989,260:48-57.
[35]King G,Vita-Finzi C.Active folding in the Algerian earth-quake of10October1980[J].Nature,1981,292:22-26.
[36]张培震,邓起东,徐锡伟,等.盲断裂,褶皱地震与新疆1906年玛纳斯地震[J].地震地质,1994,16(3),193-204.
[37]Heaton T H,Hall J F,Wald D J.Response of high-rise and base-isolated buildings to a hypothetical M W 7.0blind thrust earthquake[J].Science,1995,13:206-211.
[38]单斌,熊熊,郑勇,等.2008年5月12日M W 7.9汶川地震导致的周边断层应力变化[J].中国科学:D辑,2009,39(5):537-545.
[39]Wang R,Lorenzo-Mart F,Roth F.PSGRN/PSCMP:A new code for calculating co-and post-seismic deformation,geoid and gravity changes based on the viscoelastic-gravitational dislocation theory[J].Computers and Geosciences,2006,32(4):527-541.
[40]甘卫军研究小组.4.20芦山M7.0地震区GPS站同震位移结果.2013-04-26.http:∥www.eq-igl.ac.cn/admin/upload/files/.
[41]Parsons T,Ji C,Kirby E.Stress changes from the2008Wen-chuan earthquake and increased hazard in the Sichuan Basin[J].Nature,2008:509-510.doi:10.1038/nature07177.
[42]Toda S,Lin J,Meghraoui M,et al.12May2008M=7.9 Wenchuan,China,earthquake calculated to increase failure stress and seismicity rate on three major fault systems[J].Geophysical Research Letters,2008,35(17):L17305.doi:10.1029/2008GL034903.
[2]王卫民,郝金来,姚振兴.2013年4月20日四川芦山地震震源破裂过程反演初步结果[J].地球物理学报,2013,56(4):1412-1417.
[3]徐锡伟,韩竹军,李传友,等.四川芦山7.0级强震:一次典型的盲逆断层型地震[J].科学通报,2013,58(15)(待刊).
[4]Tapponnier P,Xu Z,Roger F,et al.Oblique stepwise rise and growth of the Tibet Plateau[J].Science,2001,294:1671-1677.
[5]Xu X,Tan X,Yu G,et al.Normal-and oblique-slip of the 2008Yutian Earthquake:Evidence for eastward block mo-tion,northern Tibetan Plateau[J].Tectonophysics,2013,584:152-165.
[6]Dong S,Zhang Y,Wu Z,et al.Surface rupture and co-seis-mic displacement produced by the MS8.0Wenchuan earth-quake of May12th,2008,Sichuan,China:Eastwards growth of the Qinghai-Tibet Plateau[J].Acta Geologica Sini-ca,2008,82(5):801-840.
[7]徐锡伟,闻学泽,叶建青,等.汶川M S 8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.
[8]徐锡伟,陈桂华,于贵华,等.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,2010,53(10):2321-1336.
[9]Xu X,Wen X,Yu G,et al.Co-seismic reverse-and oblique-slip surface faulting generated by the2008MW7.9Wenchuan earth-quake,China[J].Geology,2009,37(6):515-518.
[10]Yu G,Xu X,Klinger Y,et al.Fault-scarp features and cas-cading-rupture model for the Wenchuan earthquake(M W 7.9),eastern Tibetan Plateau,China[J].Bulletin of the Seismo-logical Society of America[J].2010,100(5B):2590-2614.
[11]Hubbard J,Shaw J H.Uplift of the Longmen Shan and Tibetan Plateau,and the2008Wenchuan(M W 7.9)earth-quake[J].Nature,2009,458:194-197.doi:10.1038/nature07837.
[12]邓起东,高翔,陈桂华,等.青藏高原昆仑—汶川地震系列与巴颜喀喇断块的最新活动[J].地学前缘,2010,17(5):163-178.
[13]Xu X,Chen W,Ma W,et al.Surface rupture of the Kunlun earthquake(M S 8.1),Northern Tibetan Plateau,China[J].Seismological Research Letters,2002,73(6):884-892.
[14]Xu X,YU G,Klinger Y.Re-evaluation of surface rupture parameters and faulting segmentation of the2001Kunlunshan earthquake(M W 7.8),Northern Tibetan Plateau,China[J].Journal of Geophysical Research,2006,111:B05316.doi:10.1029/2004JB003488.
[15]Shi F,He H,Wei Z.Coseismic horizontal shortening associ-ated with the2008Wenchuan earthquake along the Baishahe segment from high resolution satellite images[J].Journal ofAsian Earth Sciences,2012,50:164-170.
[16]孙鑫喆,徐锡伟,陈立春,等.2010年玉树地震地表破裂带典型破裂样式及其构造意义[J].地球物理学报,2012,55(1):155-170.
[17]朱艾斓,徐锡伟,周永胜,等.川西地区小震重新定位及其活动构造意义[J].地球物理学报,2005,48(3):629-636.
[18]易桂喜,闻学泽,王思维,等.由地震活动参数分析龙门山—岷山断裂带的现今活动习性与强震危险性[J].中国地震,2006,22(2):117-125.
[19]易桂喜,闻学泽,辛华,等.2008年汶川M S 8.0地震前龙门山—岷山构造带的地震活动性参数与地震视应力分布[J].地球物理学报,2011,54(6):1490-1500.
[20]Hubbard J,Shaw J H,Klinger Y.Structural setting of the 2008M W 7.9Wenchuan,China,earthquake[J].Bulletin of the Seismological Society of America,2010,100:2713-2735.
[21]谭锡斌,李元希,徐锡伟,等.低温热年代学数据对龙门山逆冲带南段新生代活动性的约束[J].地震地质,2013,35(2)(待刊).
[22]王椿镛,韩渭宾,吴建平,等.松潘-甘孜造山带地壳速度结构[J].地震学报,2003,25(3):229-241.
[23]朱介寿.汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报:自然科学版,2008,35(4):348-356.
[24]刘启元,李昱,陈九辉,等.汶川M S 8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,2009,52(2):309-319.
[25]郭飚,刘启元,陈九辉,等.川西龙门山及邻区地壳上地幔远震P波层析成像[J].地球物理学报,2009,52(2):346-355.
[26]李昱,姚华建,刘启元,等.川西地区台阵环境噪声瑞利波相速度层析成像[J].地球物理学报,2010,53(4):842-852.
[27]Zhang Z,Yuan X,Chen Y,et al.Seismic signature of the collision between the east Tibetan escape flow and the Si-chuan Basin[J].Earth and Planetary Science Letters,2010,292:254-264.
[28]Zhao G,Unsworth M J,Zhan Y,et al.Crustal structure and rheology of the Longmenshan and Wenchuan MW7.9earth-quake epicentral area from magnetotelluric data[J].Geology,2012,40(12):1139-1142.
[29]刘杰,易桂喜,张致伟,等.2013年4月20日四川芦山M7.0级地震介绍[J].地球物理学报,2013,56(4):1004-1407.
[30]曾祥方,罗艳,韩立波,等.2013年4月20日四川芦山M S 7.0地震:一个高角度逆冲地震[J].地球物理学报,2013,56(4):1418-1424.
[31]谢祖军,金笔凯,郑勇,等.近远震波形反演2013年芦山地震震源参数[J].中国科学:D辑,2013,43:1010-1019.
[32]Yeats R S,Sieh K,Allen C R.The Geology of Earthquake[M].Oxford:Oxford University Press,1997:1-568.
[33]Stein R,King G.Seismic potential revealed by surface fold-ing:1983California,earthquake[J].Science,1984,224:869-872.
[34]Stein R,Yeats R S.Hidden earthquakes[J].Scientific American,1989,260:48-57.
[35]King G,Vita-Finzi C.Active folding in the Algerian earth-quake of10October1980[J].Nature,1981,292:22-26.
[36]张培震,邓起东,徐锡伟,等.盲断裂,褶皱地震与新疆1906年玛纳斯地震[J].地震地质,1994,16(3),193-204.
[37]Heaton T H,Hall J F,Wald D J.Response of high-rise and base-isolated buildings to a hypothetical M W 7.0blind thrust earthquake[J].Science,1995,13:206-211.
[38]单斌,熊熊,郑勇,等.2008年5月12日M W 7.9汶川地震导致的周边断层应力变化[J].中国科学:D辑,2009,39(5):537-545.
[39]Wang R,Lorenzo-Mart F,Roth F.PSGRN/PSCMP:A new code for calculating co-and post-seismic deformation,geoid and gravity changes based on the viscoelastic-gravitational dislocation theory[J].Computers and Geosciences,2006,32(4):527-541.
[40]甘卫军研究小组.4.20芦山M7.0地震区GPS站同震位移结果.2013-04-26.http:∥www.eq-igl.ac.cn/admin/upload/files/.
[41]Parsons T,Ji C,Kirby E.Stress changes from the2008Wen-chuan earthquake and increased hazard in the Sichuan Basin[J].Nature,2008:509-510.doi:10.1038/nature07177.
[42]Toda S,Lin J,Meghraoui M,et al.12May2008M=7.9 Wenchuan,China,earthquake calculated to increase failure stress and seismicity rate on three major fault systems[J].Geophysical Research Letters,2008,35(17):L17305.doi:10.1029/2008GL034903.
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