汶川地震序列早期特征及成因探讨
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摘要
地震序列的特征和震型判定工作有助于抗震救灾工作的开展,对其发生成因的研究是解决地震预报难题必须面对的科学问题。汶川8.0级地震序列的初步研究表明:①余震沿龙门山断裂带分布于宽100km,长约330km的带状区域内,并侧向于主震震中的北侧;②序列发展初期有2个快速衰减过程;③序列类型为主震—余震型,最大强余震6.4级;④序列的空间演化过程,强余震震源机制结果和地震精确定位结果分析表明,序列具有分段特征;⑤8.0级地震的发震构造是龙门山断裂带,发震构造在剖面上呈现出"犁形"或"铲形"。地球物理勘探和壳、幔结构反演结果表明,自青藏高原穿越龙门山到四川盆地存在地幔阶梯,上地幔阶梯的阻挡作用使得物质东移速率减慢,并蕴积了汶川8.0级地震所需能量。地震的产生正是东西向应力平衡被打破的结果,余震沿龙门山断裂的分布是高原地壳在印度板块的推挤作用下向北北东方向的运动得以继续的表现。整个龙门山断裂带都参与了活动,龙门山断裂带北端作为断裂带的止裂端与南段同期活动。
The features of Wenchuan M8.0 earthquake and judgment of the sequences are useful to develop the work of earthquake relief.The research of the causes of great earthquakes are useful to realize the earthquake prediction and forecast.The study results show that: ① The aftershocks of the earthquake distributed along the Longmenshan mountain fault zone,and mainly in the north side of the mainshock,the earthquake zone is 100km width,about 330km length.②There were two rapid energy attenuation in early period of the sequence.③ The type of Wenchuan M8.0 earthquake sequences was judged to be main-aftershock pattern.The max aftershock is Qingchuan M6.4 earthquake on May 25,2008.④ Time-space evolution,the focal mechanism of bigger aftershock and the results of aftershock precisely location in the sequence proved that the sequence shows an obvious segmented feature.⑤ The Longmenshan mountain fault zone is major triggering seismic fault with spade fault profile.A step of moho depth form Tibet to Sichuan basin,crossed through Longmenshan mountain,was revealed by the result of geophysical exploration and inversion of Crust-Mantle velocity structure.The step is a barrier of the crust of Tibet eastward movement and makes the movement rate slowed down and great energy of M8.0 Wenchuan accumulated.The broken east-westward stress balance generates the earthquake.The aftershocks of the sequences show zonal distribution along to Longmenshan mountain fault zone,and it's the result of north-eastward movement under the broaching of India plate.The south section and north end of the Longmenshan mountain fault zone moved simultaneously and the all fault zone was actived.
The features of Wenchuan M8.0 earthquake and judgment of the sequences are useful to develop the work of earthquake relief.The research of the causes of great earthquakes are useful to realize the earthquake prediction and forecast.The study results show that: ① The aftershocks of the earthquake distributed along the Longmenshan mountain fault zone,and mainly in the north side of the mainshock,the earthquake zone is 100km width,about 330km length.②There were two rapid energy attenuation in early period of the sequence.③ The type of Wenchuan M8.0 earthquake sequences was judged to be main-aftershock pattern.The max aftershock is Qingchuan M6.4 earthquake on May 25,2008.④ Time-space evolution,the focal mechanism of bigger aftershock and the results of aftershock precisely location in the sequence proved that the sequence shows an obvious segmented feature.⑤ The Longmenshan mountain fault zone is major triggering seismic fault with spade fault profile.A step of moho depth form Tibet to Sichuan basin,crossed through Longmenshan mountain,was revealed by the result of geophysical exploration and inversion of Crust-Mantle velocity structure.The step is a barrier of the crust of Tibet eastward movement and makes the movement rate slowed down and great energy of M8.0 Wenchuan accumulated.The broken east-westward stress balance generates the earthquake.The aftershocks of the sequences show zonal distribution along to Longmenshan mountain fault zone,and it's the result of north-eastward movement under the broaching of India plate.The south section and north end of the Longmenshan mountain fault zone moved simultaneously and the all fault zone was actived.
引文
[1]蒋海昆,黎明晓,吴琼,等.汶川8.0级地震序列及相关问题讨论[J].地震地质,2008,30(3):746-757.
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[3]吴开统,焦远碧,吕培苓,等.地震序列概论[M].北京:北京大学出版社,1990:97-98.
[4]蒋海昆,曲延军,李永莉,等.中国大陆中强地震余震序列的部分统计特征[J].地球物理学报,2006,49(4):1 110-1 117.
[5]谷继成,谢小碧,赵莉.强余震的时空分布规律及其理论解释[J].地球物理学报,1979,22(1):32-46.
[6]朱传镇,王林瑛.震群信息熵异常与地震预测[A].地震预报方法实用化攻关文集(地震学专辑)[C].北京:地震出版社,1989:229-242.
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[9]哈佛大学.http://www.globalcmt.org/CMTsearch.html
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[13]徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.
[14]张培震,徐锡伟,闻学泽,等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,2008,51(4):1 066-1 073.
[15]Molnar P.,Tapponnier P.Cenozoic Tectonics of Asia:Effects of a Continental Collision:Features of recentcontinental tectonics in Asia can be interpreted as re-sults of the India-Eurasia Collision[J].Science,1975,189:419.
[16]Tapponnier,P,Molnar P.Active faulting and tectonicsin China[J].J Geophys Res,1977,82:2 905.
[17]Deng Qidong.Kinematic features and slip rates of theQuaternary active faulting of Qinghai-Xizang(Tibet)Plateau and kinematic characteristics of the Plateauand secondary blocks within it[M].Chengdu:Hima-layan Symposiums,China,1984:70-72.
[18]Auouac J.P.,Tapponnier P.Kinematic model of ac-tive deformation in Central Asia[J].Geophys ResLett,1993,20:895.
[19]Meyer B.,Tapponnier P.,Bourjot L.,et al.Crustalthickening in Gansu-Qinghai,lithospheric mantle sub-duction,and oblique,strike-slip controlled growth ofthe Tibet plateau[J].Geophys J Int,1998,135:1-47.
[20]王谦身,滕吉文,张永谦,等.龙门山断裂系及邻区地壳重力均衡效应与汶川地震[J].地球物理学报,2008,23(6):1 664-1 670.
[21]刘元龙,郑建昌.用地球物理资料研究中国深部地壳构造及矿产分布[J].长春地质学院学报,1993,23(4):430-438.
[22]滕吉文,白登海,杨辉,等.2008汶川Ms8.0地震发生的深层过程和动力学响应[J].地球物理学报,2008,51(5):1 385-1 042.
[2]国家地震局科技监测司.地震学分析预报方法程式指南[M].北京:地震出版社,1990:20-23.
[3]吴开统,焦远碧,吕培苓,等.地震序列概论[M].北京:北京大学出版社,1990:97-98.
[4]蒋海昆,曲延军,李永莉,等.中国大陆中强地震余震序列的部分统计特征[J].地球物理学报,2006,49(4):1 110-1 117.
[5]谷继成,谢小碧,赵莉.强余震的时空分布规律及其理论解释[J].地球物理学报,1979,22(1):32-46.
[6]朱传镇,王林瑛.震群信息熵异常与地震预测[A].地震预报方法实用化攻关文集(地震学专辑)[C].北京:地震出版社,1989:229-242.
[7]刘正荣,孔绍麟.地震频度衰减与地震预报[J].地震研究,1986,9(1):1-12.
[8]陈运泰,许力生,张勇,等.2008年5月12日汶川特大地震震源特性分析报告.2008:http://www.csi.as.cn/Sichuan/chenyuntai.pdf
[9]哈佛大学.http://www.globalcmt.org/CMTsearch.html
[10]朱艾澜,徐锡伟,刁桂苓,等.汶川Ms8.0级地震部分余震重新定位及地震构造初步分析[J].地震地质,2008,30(3):759-767.
[11]Waldnuser F,Ellsworth W.A double-difference earth-quake location algorithm:method and application tothe northern Hayward Fault[J].California BullSeism Soc Am,2000,90(6):1 353-1 368.
[12]赵珠,范军,郑斯华,等.龙门山推覆构造带地壳速度结构和震源位置的精确修订[J].地震学报,1997,19(6):615-622.
[13]徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.
[14]张培震,徐锡伟,闻学泽,等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,2008,51(4):1 066-1 073.
[15]Molnar P.,Tapponnier P.Cenozoic Tectonics of Asia:Effects of a Continental Collision:Features of recentcontinental tectonics in Asia can be interpreted as re-sults of the India-Eurasia Collision[J].Science,1975,189:419.
[16]Tapponnier,P,Molnar P.Active faulting and tectonicsin China[J].J Geophys Res,1977,82:2 905.
[17]Deng Qidong.Kinematic features and slip rates of theQuaternary active faulting of Qinghai-Xizang(Tibet)Plateau and kinematic characteristics of the Plateauand secondary blocks within it[M].Chengdu:Hima-layan Symposiums,China,1984:70-72.
[18]Auouac J.P.,Tapponnier P.Kinematic model of ac-tive deformation in Central Asia[J].Geophys ResLett,1993,20:895.
[19]Meyer B.,Tapponnier P.,Bourjot L.,et al.Crustalthickening in Gansu-Qinghai,lithospheric mantle sub-duction,and oblique,strike-slip controlled growth ofthe Tibet plateau[J].Geophys J Int,1998,135:1-47.
[20]王谦身,滕吉文,张永谦,等.龙门山断裂系及邻区地壳重力均衡效应与汶川地震[J].地球物理学报,2008,23(6):1 664-1 670.
[21]刘元龙,郑建昌.用地球物理资料研究中国深部地壳构造及矿产分布[J].长春地质学院学报,1993,23(4):430-438.
[22]滕吉文,白登海,杨辉,等.2008汶川Ms8.0地震发生的深层过程和动力学响应[J].地球物理学报,2008,51(5):1 385-1 042.
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