地震活动时空演化中看到的龙门山断裂带地震孕育的几个现象
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摘要
龙门山断裂带在先后5年中发生了2008年汶川M S8强震和2013芦山M S7强震。研究龙门山断裂的地震活动特点,分析地震发展形势成为人们关注的焦点。文中从龙门山断裂带40多年的地震时空演化出发探讨了汶川地震孕育过程中的几个现象:1)孕震范围远小于发震范围,说明在有限断层段上孕育的地震在快速失稳过程中可以连接和扩展成规模很大的失稳断层;2)汶川地震前孕震区小震密集,持续了8年以上,而无明显错动和变形,意味着汶川断层段可能经历了强烈的碎裂方式的挤压应变,在碎裂达到一定程度后失稳;3)为进一步了解震前主震区附近的变化,研究了紫坪铺水库专用台网记录的2004年以来主震附近区域的小震活动的时空过程。结果显示,震前主震附近区域的地震活动曾在2005年10月和2006年10月发生过2次沿断层走向的扩展,扩展时间恰巧与紫坪铺水库2次高水位相呼应。其中,2006年10月地震活动的扩展范围大,震级高。这对说明汶川地震最后的失稳过程十分重要。此外,文中还讨论了汶川地震的发生过程与断层几何相关以及芦山地震没有直接发生在汶川地震后,而是发生在多年后的可能原因。研究结果有助于认识逆断层型强震孕育过程。
Within almost five years,the 2008 Wenchuan MS 8.0 and 2013 Lushan MS 7.0 earthquakes ruptured the Longmenshan Fault zone successively.The characteristics of earthquakes and their development tendency on this fault zone have been a focus of subject of research.This article attempts to explore some features of seismic preparation process of the 2008 Wenchuan event from temporalspatial evolution of earthquakes along the Longmenshan Fault zone during more than 40 years.(1) The spatial range of the earthquake preparation,or seismic nucleation,is much smaller than that of coseismic rupturing.It indicates that the seismic source,probably consisting of some small asperities or barriers,prepared on a finite fault segment can be connected and expand into a large-scale rupture section along the fault when the fast instability occurs at the source.(2) Prior to the 2008 Wenchuan giant shock,its preparation area had experienced a dense distribution of small earthquakes for eight years or more,while no conspicuous slip and deformation were observed on the surface.This implies that the seismogenic fault segment of the Wenchuan event on the Longmenshan Fault was undergoing probably compressive deformation,accompanied with cataclastic process.When the cataclastic deformation of the great-shock source reached a critical state,fault instability occurred along the fault with rapid rupturing.(3) To further study the variations of the main-shock area prior to the event,this article analyzes the temporal-spatial processes of small earthquakes around the main shock since 2004 recorded by a special seismic network in the Zipingpu reservoir.The results indicate that the scope of the seismicity expanding along the fault took place along the fault in October 2005 and October 2006,respectively,in accordance with the time when the reservoir reached its high water level.Among them,the second expanding from October 2006 covered a relatively large area and with relatively big magnitudes,implying great importance for the study of the final instability process of the 2008 Wenchuan huge earthquake.Besides,this paper discusses the correlation of the rupturing process of the 2008 Wenchuan giant event with the geometry of the fault and the reason why the 2013 Lushan earthquake occurred many years after the Wenchuan event rather than immediately following this giant shock like usual big aftershocks.The research results are helpful for understanding of seismogenic processes of major earthquakes of the thrust type.
Within almost five years,the 2008 Wenchuan MS 8.0 and 2013 Lushan MS 7.0 earthquakes ruptured the Longmenshan Fault zone successively.The characteristics of earthquakes and their development tendency on this fault zone have been a focus of subject of research.This article attempts to explore some features of seismic preparation process of the 2008 Wenchuan event from temporalspatial evolution of earthquakes along the Longmenshan Fault zone during more than 40 years.(1) The spatial range of the earthquake preparation,or seismic nucleation,is much smaller than that of coseismic rupturing.It indicates that the seismic source,probably consisting of some small asperities or barriers,prepared on a finite fault segment can be connected and expand into a large-scale rupture section along the fault when the fast instability occurs at the source.(2) Prior to the 2008 Wenchuan giant shock,its preparation area had experienced a dense distribution of small earthquakes for eight years or more,while no conspicuous slip and deformation were observed on the surface.This implies that the seismogenic fault segment of the Wenchuan event on the Longmenshan Fault was undergoing probably compressive deformation,accompanied with cataclastic process.When the cataclastic deformation of the great-shock source reached a critical state,fault instability occurred along the fault with rapid rupturing.(3) To further study the variations of the main-shock area prior to the event,this article analyzes the temporal-spatial processes of small earthquakes around the main shock since 2004 recorded by a special seismic network in the Zipingpu reservoir.The results indicate that the scope of the seismicity expanding along the fault took place along the fault in October 2005 and October 2006,respectively,in accordance with the time when the reservoir reached its high water level.Among them,the second expanding from October 2006 covered a relatively large area and with relatively big magnitudes,implying great importance for the study of the final instability process of the 2008 Wenchuan huge earthquake.Besides,this paper discusses the correlation of the rupturing process of the 2008 Wenchuan giant event with the geometry of the fault and the reason why the 2013 Lushan earthquake occurred many years after the Wenchuan event rather than immediately following this giant shock like usual big aftershocks.The research results are helpful for understanding of seismogenic processes of major earthquakes of the thrust type.
引文
陈运泰.2008a.汶川大地震的震源破裂过程[R].海峡两岸防震减灾学术研讨会.北京.2008年6月27—28日.CHEN Yun-tai.2008a.Rupturing processes of the Wenchuan great earthquake[R].Presented at the Symposium on Earthquake Prevention and Disaster Reduction in Both Sides of the Taiwan Straits.Beijing.27—28 June 2008(in Chinese).
陈运泰.2008b.汶川地震的成因断层、破裂过程与成灾机理[R].“科学技术与抗震救灾”科学技术论坛.成都.2008年7月24—26日.CHEN Yun-tai.2008b.The genesis fault,rupturing processes and mechanisms of disaster generation[R].Presented at the Forum of Science and Technology:“Science and Technology,Earthquake Resistance and Disaster Relief”.Chengdu.24—26 July 2008(in Chinese).
陈运泰,杨智娴,张勇,等.2013.从汶川地震到芦山地震[J].中国科学(D辑),43(6):1064—1072.CHEN Yun-tai,YANG Zhi-xian,ZHANG Yong,et al.2013.From 2008 Wenchuan earthquake to 2013 Lushan earthquake[J].Scientia Sinica Terrae(Ser D),43(6):1064—1072(in Chinese).
邓起东主编.2007.中国活动构造图[M].北京:地震出版社.DENG Qi-dong(ed).2007.Map of Active Tectonics in China[M].Seismological Press,Beijing(in Chinese).
邓起东,陈社发,赵小麟.1994.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,16(4):389—403.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin.1995.Tectonics,seismicity and dynamics of Longmenshan Mountains and Its adjacent regions[J].Seismology and Geology,16(4):389—403(in Chinese).
杜方,闻学泽,张培震,等.2009.2008年汶川8.0级地震前横跨龙门山断裂带的震间形变[J].地球物理学报,52(11):2729—2738.doi:10.3969/j.issn.0001—5733.DU Fang,WEN Xue-ze,ZHANG Pei-zhen,et al.2009.Interseismic deformation across the Longmenshan Fault zone before the 2008 Wenchuan M8.0 earthquake[J].Chinese J Geophys,52(11):2729—2738(in Chinese).
刘启元,陈九辉,李顺成,等.2008.汶川M S8.0地震:川西流动地震台阵观测数据的初步分析[J].地震地质,30(3):584—596.LIU Qi-yuan,CHEN Jiu-hui,LI Shun-chen,et al.2008.The M S8.0 Wenchuan earthquake:Preliminary results from the western Sichuan mobile seismic array observations[J].Seismology and Geology,30(3):584—596(in Chinese).
刘启元,李昱,陈九辉,等.2009.汶川M S8.0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,52(2):309—319.LIU Qi-yuan,LI Yu,CHEN Jiu-hui,et al.2009.Wenchuan M S8.0 earthquake:Preliminary study of the S-wave velocity structure of the crust and upper mantle[J].Chin J Geophys,52(2):309—319(in Chinese).
吕江宁,沈正康,王敏.2003.川滇地区现代地壳运动速度场与活动块体模型研究[J].地震地质,25(4):543—554.L Jiang-ning,SHEN Zheng-kang,WANG Min.2003.Contemporary crustal deformation and active tectonic block model of the Sichuan-Yunnan region,China[J].Seismology and Geology,25(4):543—554(in Chinese).
马瑾,陈顺云,扈小燕,等.2010.大陆地表温度场的时空变化与现今构造活动[J].地学前缘,17(4):1—14.MA Jin,CHEN Shun-yun,HU Xiao-yan,et al.2010.Spatial-temporal variation of the land surface temperature field and present-day tectonic activity[J].Earth Science Frontiers,17(4):1—14(in Chinese).
马丽芳主编.2002.中国地质图集[M].北京:地质出版社.MA Li-fang(ed).2002.Geological Atlas of China[M].Geological Publishing House,Beijing(in Chinese).
闻学泽,张培震,杜方,等.2009.2008年汶川8.0级地震发生的历史与现今地震活动背景[J].地球物理学报,52(2):444—454.WEN Xue-ze,ZHANG Pei-zhen,DU Fang,et al.2009.The background of historical and modern seismic activities of the occurrence of the 2008 M S8.0 Wenchuan,Sichuan,earthquake[J].Chinese J GeoPhys,52(2):444—454(in Chinese).
徐锡伟,闻学泽,陈桂华,等.2008a.巴颜喀拉地块东部龙日坝断裂带的发现及其大地构造意义[J].中国科学(D辑),38(5):529—542.doi:10.1007/s11430-008-0097—1.XU Xi-wei,WEN Xue-ze,CHEN Gui-hua,et al.2008a.Discovery of the Longriba Fault zone in eastern Bayan Har block,China and its tectonic implication[J].Science in China(Ser D),51(9):1209—1223.
徐锡伟,闻学泽,叶建青.2008b.汶川M S8.0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.2008b.The M S8.0 Wenchuan earthquake surface ruptures and its seismogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
易桂喜,闻学泽,辛华,等.2013.龙门山断裂带南段应力状态与强震危险性研究[J].地球物理学报,56(4):1112—1120.doi:10.6038/cjg20130407.YI Gui-xi,WEN Xue-ze,XIN Hua,et al.2013.Stress state and major-earthquake risk on southern segment of Longmen Shan Fault zone[J].Chinese J Geophys,56(4):1112—1120(in Chinese).
张培震,徐锡伟,闻学泽.2008.2008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,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May 12 Wenchuan earthquake,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
张勇,冯万鹏,许力生,等.2008.2008年汶川大地震的时空破裂过程[J].中国科学(D辑),38(10):1186—1194.doi:10.1007/s11430-008-0097—1.ZHANG Yong,FENG Wan-peng,XU Li-sheng,et al.2009.Spatio-temporal rupture process of the 2008 great Wenchuan earthquake[J].Science in China(Ser D),52(2):145—154.
中国地震局监测预报司.2009.汶川8.0级地震科学研究报告[M].北京:地震出版社.Department of Monitoring and Prediction,China Earthquake Administration.2009.Scientific research report on the Wenchuan M S8.0 Earthquake[M].Seismological Press,Beijing(in Chinese).
“2006—2020年中国大陆地震危险区与地震灾害损失预测研究”项目组.2007.2006—2020年中国大陆地震危险区与地震灾害损失预测研究[M].北京:地震出版社.Research group of“Researches on Earthquake Risk Regions and Losses Prediction of China Continent during 2006 to2020”.2007.Researches on Earthquake Risk Regions and Losses Prediction of China Continent during 2006 to2020[M].Seismological Press,Beijing(in Chinese).
Chen J H,Froment B,Liu Q Y,et al.2010.Distribution of seismic wave speed changes associated with the 12 May 2008M W7.9 Wenchuan earthquake[J].Geophysical Research Letters,37(18).doi:10.1029/2010GL044582,2010.
Chen J,Liu Q,Li S,et al.2008.Dense seismic array observation in the Wenchuan M8.0 earthquake region[J].Eos Trans AGU,89(53):Fall Meet Suppl Abstract S23E-03.
Parsons T,Ji C,Kirby E.2008.Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan Basin[J].Nature,454:509—510.doi:10.1038/nature07177.
Shen Z K,Lü J,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibetan plateau[J].Journal of Geophysical Research,110(B11):B11409.doi:10.1029/2004JB003421.
Shen Z K,Sun J,Zhang P,et al.2009.Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchuan earthquake[J].Nature Geoscience,2(10):718—724.
Xu X,Wen X,Yu G,et al.2009.Coseismic reverse-and oblique-slip surface faulting generated by the 2008 M W7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.doi:10.1130/G25462A.1.
Yang Z X,Waldhauser F,Chen Y T,et al.2005.Double-difference relocation of earthquakes in central-western China,1992-1999[J].Journal of Seismology,9(2):241—264.doi:10.1007/s10950-005-3988-z.
Zhang P Z.2013.Beware of slowly slipping faults[J].Nature Geoscience,6(5):323—324.doi:10.1038/ngeo1811.
Zhang P Z,Shen Z,Wang M,et al.2004.Continuous deformation of the Tibetan plateau from global positioning system data[J].Geology,32(9):809—812.doi:10.1130/G20554.
Zhang K L,Wei D P.2011.Implications from the kinematic pattern of the Longmenshan region[J].Tectonophysics,504(1):57—64.doi:10.1016/j.tecto.2011.01.019.
Ма Цзинь,Лю Личиань,Лю Ксиа,Лю.Пэшун,Чэнь Шуньюнь,Ма Сэнли,Гуо Уаньшуан.2009.Вэньчаньское землетрясение в мае 2008 г.ВКитае.геология.сейсмлогия.Природа,5:39—47.
陈运泰.2008b.汶川地震的成因断层、破裂过程与成灾机理[R].“科学技术与抗震救灾”科学技术论坛.成都.2008年7月24—26日.CHEN Yun-tai.2008b.The genesis fault,rupturing processes and mechanisms of disaster generation[R].Presented at the Forum of Science and Technology:“Science and Technology,Earthquake Resistance and Disaster Relief”.Chengdu.24—26 July 2008(in Chinese).
陈运泰,杨智娴,张勇,等.2013.从汶川地震到芦山地震[J].中国科学(D辑),43(6):1064—1072.CHEN Yun-tai,YANG Zhi-xian,ZHANG Yong,et al.2013.From 2008 Wenchuan earthquake to 2013 Lushan earthquake[J].Scientia Sinica Terrae(Ser D),43(6):1064—1072(in Chinese).
邓起东主编.2007.中国活动构造图[M].北京:地震出版社.DENG Qi-dong(ed).2007.Map of Active Tectonics in China[M].Seismological Press,Beijing(in Chinese).
邓起东,陈社发,赵小麟.1994.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,16(4):389—403.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin.1995.Tectonics,seismicity and dynamics of Longmenshan Mountains and Its adjacent regions[J].Seismology and Geology,16(4):389—403(in Chinese).
杜方,闻学泽,张培震,等.2009.2008年汶川8.0级地震前横跨龙门山断裂带的震间形变[J].地球物理学报,52(11):2729—2738.doi:10.3969/j.issn.0001—5733.DU Fang,WEN Xue-ze,ZHANG Pei-zhen,et al.2009.Interseismic deformation across the Longmenshan Fault zone before the 2008 Wenchuan M8.0 earthquake[J].Chinese J Geophys,52(11):2729—2738(in Chinese).
刘启元,陈九辉,李顺成,等.2008.汶川M S8.0地震:川西流动地震台阵观测数据的初步分析[J].地震地质,30(3):584—596.LIU Qi-yuan,CHEN Jiu-hui,LI Shun-chen,et al.2008.The M S8.0 Wenchuan earthquake:Preliminary results from the western Sichuan mobile seismic array observations[J].Seismology and Geology,30(3):584—596(in Chinese).
刘启元,李昱,陈九辉,等.2009.汶川M S8.0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,52(2):309—319.LIU Qi-yuan,LI Yu,CHEN Jiu-hui,et al.2009.Wenchuan M S8.0 earthquake:Preliminary study of the S-wave velocity structure of the crust and upper mantle[J].Chin J Geophys,52(2):309—319(in Chinese).
吕江宁,沈正康,王敏.2003.川滇地区现代地壳运动速度场与活动块体模型研究[J].地震地质,25(4):543—554.L Jiang-ning,SHEN Zheng-kang,WANG Min.2003.Contemporary crustal deformation and active tectonic block model of the Sichuan-Yunnan region,China[J].Seismology and Geology,25(4):543—554(in Chinese).
马瑾,陈顺云,扈小燕,等.2010.大陆地表温度场的时空变化与现今构造活动[J].地学前缘,17(4):1—14.MA Jin,CHEN Shun-yun,HU Xiao-yan,et al.2010.Spatial-temporal variation of the land surface temperature field and present-day tectonic activity[J].Earth Science Frontiers,17(4):1—14(in Chinese).
马丽芳主编.2002.中国地质图集[M].北京:地质出版社.MA Li-fang(ed).2002.Geological Atlas of China[M].Geological Publishing House,Beijing(in Chinese).
闻学泽,张培震,杜方,等.2009.2008年汶川8.0级地震发生的历史与现今地震活动背景[J].地球物理学报,52(2):444—454.WEN Xue-ze,ZHANG Pei-zhen,DU Fang,et al.2009.The background of historical and modern seismic activities of the occurrence of the 2008 M S8.0 Wenchuan,Sichuan,earthquake[J].Chinese J GeoPhys,52(2):444—454(in Chinese).
徐锡伟,闻学泽,陈桂华,等.2008a.巴颜喀拉地块东部龙日坝断裂带的发现及其大地构造意义[J].中国科学(D辑),38(5):529—542.doi:10.1007/s11430-008-0097—1.XU Xi-wei,WEN Xue-ze,CHEN Gui-hua,et al.2008a.Discovery of the Longriba Fault zone in eastern Bayan Har block,China and its tectonic implication[J].Science in China(Ser D),51(9):1209—1223.
徐锡伟,闻学泽,叶建青.2008b.汶川M S8.0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.2008b.The M S8.0 Wenchuan earthquake surface ruptures and its seismogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
易桂喜,闻学泽,辛华,等.2013.龙门山断裂带南段应力状态与强震危险性研究[J].地球物理学报,56(4):1112—1120.doi:10.6038/cjg20130407.YI Gui-xi,WEN Xue-ze,XIN Hua,et al.2013.Stress state and major-earthquake risk on southern segment of Longmen Shan Fault zone[J].Chinese J Geophys,56(4):1112—1120(in Chinese).
张培震,徐锡伟,闻学泽.2008.2008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,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May 12 Wenchuan earthquake,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
张勇,冯万鹏,许力生,等.2008.2008年汶川大地震的时空破裂过程[J].中国科学(D辑),38(10):1186—1194.doi:10.1007/s11430-008-0097—1.ZHANG Yong,FENG Wan-peng,XU Li-sheng,et al.2009.Spatio-temporal rupture process of the 2008 great Wenchuan earthquake[J].Science in China(Ser D),52(2):145—154.
中国地震局监测预报司.2009.汶川8.0级地震科学研究报告[M].北京:地震出版社.Department of Monitoring and Prediction,China Earthquake Administration.2009.Scientific research report on the Wenchuan M S8.0 Earthquake[M].Seismological Press,Beijing(in Chinese).
“2006—2020年中国大陆地震危险区与地震灾害损失预测研究”项目组.2007.2006—2020年中国大陆地震危险区与地震灾害损失预测研究[M].北京:地震出版社.Research group of“Researches on Earthquake Risk Regions and Losses Prediction of China Continent during 2006 to2020”.2007.Researches on Earthquake Risk Regions and Losses Prediction of China Continent during 2006 to2020[M].Seismological Press,Beijing(in Chinese).
Chen J H,Froment B,Liu Q Y,et al.2010.Distribution of seismic wave speed changes associated with the 12 May 2008M W7.9 Wenchuan earthquake[J].Geophysical Research Letters,37(18).doi:10.1029/2010GL044582,2010.
Chen J,Liu Q,Li S,et al.2008.Dense seismic array observation in the Wenchuan M8.0 earthquake region[J].Eos Trans AGU,89(53):Fall Meet Suppl Abstract S23E-03.
Parsons T,Ji C,Kirby E.2008.Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan Basin[J].Nature,454:509—510.doi:10.1038/nature07177.
Shen Z K,Lü J,Wang M,et al.2005.Contemporary crustal deformation around the southeast borderland of the Tibetan plateau[J].Journal of Geophysical Research,110(B11):B11409.doi:10.1029/2004JB003421.
Shen Z K,Sun J,Zhang P,et al.2009.Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchuan earthquake[J].Nature Geoscience,2(10):718—724.
Xu X,Wen X,Yu G,et al.2009.Coseismic reverse-and oblique-slip surface faulting generated by the 2008 M W7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.doi:10.1130/G25462A.1.
Yang Z X,Waldhauser F,Chen Y T,et al.2005.Double-difference relocation of earthquakes in central-western China,1992-1999[J].Journal of Seismology,9(2):241—264.doi:10.1007/s10950-005-3988-z.
Zhang P Z.2013.Beware of slowly slipping faults[J].Nature Geoscience,6(5):323—324.doi:10.1038/ngeo1811.
Zhang P Z,Shen Z,Wang M,et al.2004.Continuous deformation of the Tibetan plateau from global positioning system data[J].Geology,32(9):809—812.doi:10.1130/G20554.
Zhang K L,Wei D P.2011.Implications from the kinematic pattern of the Longmenshan region[J].Tectonophysics,504(1):57—64.doi:10.1016/j.tecto.2011.01.019.
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