2008年10月6日当雄M_s6.6级地震破裂过程
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摘要
2008年10月6日16时30分(北京时间),西藏自治区拉萨市当雄县发生M_s6.6级地震.震中位于亚东谷露近南北向裂谷带北段,是该活动构造带近年来发生的一次较大地震.我们利用中国地震台网中心(CENC)和美国地震学联合研究所(IRIS)提供的宽频带地震记录资料,基于点源和有限断层模型,通过波形拟合反演了该地震的震源过程.结果表明,本次地震的发震断层面走向为183.3°,倾角为49.5°,滑动角约为-115°,最大滑动量达130 cm,地震震源的深度为9.6 km,地震的标量地震矩为2.85×10~(18)N·m,破裂持续时间约10 s.根据地震破裂的几何学和运动学特征,推测该地震主要发生在亚东—谷露南北向裂谷活动构造带内的一个高角度西倾断层上,是一个以拉张为主且有一定的右旋分量的破裂事件,这与青藏高原现今GPS测量所揭示的该地区地壳运动特征基本一致,暗示了青藏高原南部从西向东地表运动从北北东向到南东东向的运动学转变所导致的地壳在近东西方向上的拉张变形特征.
The rupture process of the Oct.6, 2008 Damxung earthquake (M_s6.6) is studied by using the point source and finite fault model.The observed broadband seismograms used in the inversion were retrieved from DMC (Data Manager Center) of China Earthquake Networks Center (CENC) and of Incorporated Research Institute for Seismology (IRIS).Historical earthquake records indicated that this event is one of the strongest earthquakes in central Tibet in recent years, and its epicenter is located around the N-S trended Yadong-Golug rift zone in southern Tibet.Our inversion results show that the earthquake occurred on a west-dipping normal fault with the focal depth of 9.6 km, the fault plane has a strike of 183.3°, a dip of 49.5°. The rupture process lasted about 10 seconds with a maximum slip reaching 130 cm, consistent with a moment release of 2.84×10~(18) N·m.The dynamic rupture process obtained in this study consists with the crustal movement obtained from GPS observations, implying that this earthquake was triggered by extension stress induced by transition of crustal niovement from the direction of NNE to SSE from central southern Tibet to the eastern Himalaya Syntax.
The rupture process of the Oct.6, 2008 Damxung earthquake (M_s6.6) is studied by using the point source and finite fault model.The observed broadband seismograms used in the inversion were retrieved from DMC (Data Manager Center) of China Earthquake Networks Center (CENC) and of Incorporated Research Institute for Seismology (IRIS).Historical earthquake records indicated that this event is one of the strongest earthquakes in central Tibet in recent years, and its epicenter is located around the N-S trended Yadong-Golug rift zone in southern Tibet.Our inversion results show that the earthquake occurred on a west-dipping normal fault with the focal depth of 9.6 km, the fault plane has a strike of 183.3°, a dip of 49.5°. The rupture process lasted about 10 seconds with a maximum slip reaching 130 cm, consistent with a moment release of 2.84×10~(18) N·m.The dynamic rupture process obtained in this study consists with the crustal movement obtained from GPS observations, implying that this earthquake was triggered by extension stress induced by transition of crustal niovement from the direction of NNE to SSE from central southern Tibet to the eastern Himalaya Syntax.
引文
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[16] 吴中海,叶培盛,吴珍汉.2008年10月6日当雄M_s6． 6级强震的地震烈度控震构造和发震机理.地质通报,2009,28(6) :713～725 Wu Z H,Ye P S,Wu Z H.The seismic intensity,seismogenic tectonics and mechanism of the M_s6． 6 Damxung earthquake happened on October 6,2008 in southern Tibet,China.Geological Bulletin of China(in Chinese),2009,28(6) :713～725
[17] Lomax A,Michelini A,Piarsnesi A.An energy duration procedure for rapid and accurate determination of earthquake magnitude and tsunamigenic potential.Geophys.J.Int.,2007,170:1195～1209
[18] Molnar P,Tapponnier P.Active tectonics of Tibet.J.Geophys.Res,1978,83(B1l):5361～5375
[19] Harrison T M,Copeland P,Kidd W S F,Yin A.Raising Tibet.Science,1992,255:1663～1670
[20] Molnar P,England P,Martinod J.Mantle dynamics,uplift of the Tibetan Plateau,and the India monsoon.Rev.Geophy.,1993,31:357～396
[21] Mercier J L,Armijo R,Tapponnier P,et al.Change from Tertiary compression to Quaternary extension in southern Tibet during the India Asia collision.Tectonics,1987,6:275～304
[22] Molnar P,Tapponnier P.Cenozoic tectonics of Asia:effects of a continental collision.Science,1975,183:419～426
[23] Molnar P,Chen W P.Focal depths and fault plane solutions of earthquakes under the Tibetan plateau.J.Geophys.Res.,1983,88:1180～1196
[24] He J,Lu S,Wang X.Mechanical relation between crustal rheology,effective fault friction,and strike-slip distribution among the Xiaojiang fault system,southeastern Tibet.Journal of Asian Earth Sciences,2009,34,363～375
[25] He J,Cherry J.late Quaternary slip rates of the Altyn Tagh,the Kunlun and Karakorum faults(Tibet)from 3D mechanical modeling.Earth Planet.Sci.Lett.,2008,274:50～58
[26] Liu M,Yang Y.The collapse of Tibetan plateau:Insights from 3-D finite element modeling.J.Geophys.Res.,2003,108(B8) ,2361,doi:10． 1029/2002JB002248
[2] Armijo R,Tapponier P,Mercier J L,Han T L.Quartenary extension in Southern Tibet:field observations and tectonic implications.J.Geophys.Res.,1986,91(B14) :13803～13872
[3] Cogan M J,Nelson K D,Kidd W S F,et al.Shallow structure of the Yadong-Gulu rift,southern Tibet,from refraction analysis of project INDEPTH commom midpoint data.Tectonics,1998,17:46～61
[4] Seeber L,Armbruster J G.Some elements of continental subduction along the Himalayan front.Tectonophysics,1984,105:263～278
[5] Salichon J,Lundgren P,Delouis B,et al.Slip history of the 16 October 1999 M_w7． 1 Hector Mine Earthquake(California)from the Inversion of InSAR,GPS,and Teleseismic Data.Bull.Seismol.Soc.Am.,2004,94,2015～2027
[6] 纪晨,姚振兴.时间域内有限地震断层的反演问题.地球物理学报,1997,40:691～701 Ji C,Yao Z X.The inverse problem of finite fault study in time domain.Chinese J.Geophys.(in Chinese),1997,40:691～701
[7] 王卫民,李丽,赵连锋等.2003年2月24日新疆伽师M_s6． 5级地震震源破裂过程研究.地球物理学报,2003,48:343～351 Wang W M,Li L,Zhao L F,et al.Rupture process of Jiashi,Xinjiang earthquake(M_s6． 5) of Feb.24,2003． Chinese J.Geophys.(in Chinese),2003,48:343～351
[8] 李娟,王卫民,赵连锋等.2004年7月11日西藏M_s6． 2级地震震源破裂过程研究.地球物理学报,2005,48:843～850 Li J,Wang W M,Zhao L F,et al.Rupture process of July,11,2004,Tibet(M_s6． 2) earthquake.Chinese J.Geophys.(in Chinese),2005,48:843～850
[9] Hartzell S,Liu P C.Calculation of earthquake rupture histories using a hybrid global search algorithm:application to the 1992 Landers California earthquake.Phys.Earth.Planet.Inter.,1996,95:79～99
[10] Ji C,Wald D J,Helmberger D V.Source description of the 1999 Hector Mine,California,earthquake,Part Ⅱ:complexity of slip history.Bull.Seism.Soc.Am.,2002,92:1208～1126
[11] 郭志,高星,王卫民.2006年12月26日台湾南部滨海M_s7． 2级地震破裂过程研究.地球物理学报,2008,51:1103～1113 Guo Z,Gao X,Wang W M.Rupture process of southern Taiwan offshore M_s7． 2 earthuqake of Dec.12,2006． Chinese J.Geophys.(in Chinese),2008,51:1103～1113
[12] 姚振兴,郑天愉,曹柏如等.用P波波形资料测定中强地震震源过程的方法.地球物理学进展,1991,6:1～26 Yao Z X,Zheng T Y,Cao B R,et al,The method of determining middle and strong earthquake's process using P waveform data.Progress in Geophysics(in Chinese),1991,6:1～26
[13] Oslon A H,Apsel R.Finite fault and inversion theory with application to the 1979 Imperial Valley earthquake.Bull.Seism.Soc.Am.,1982,72(6A):1996～2001
[14] Kirkpatrick S,Gelatt C D Jr,Vecchi M P.Optimization by simulated annealing.Science,1983,220(4598) :671～680
[15] Metropolis N,Ulam S.The Monte-Carlo method.J.Amer.Stat.Assoc.,1949,44:335～341
[16] 吴中海,叶培盛,吴珍汉.2008年10月6日当雄M_s6． 6级强震的地震烈度控震构造和发震机理.地质通报,2009,28(6) :713～725 Wu Z H,Ye P S,Wu Z H.The seismic intensity,seismogenic tectonics and mechanism of the M_s6． 6 Damxung earthquake happened on October 6,2008 in southern Tibet,China.Geological Bulletin of China(in Chinese),2009,28(6) :713～725
[17] Lomax A,Michelini A,Piarsnesi A.An energy duration procedure for rapid and accurate determination of earthquake magnitude and tsunamigenic potential.Geophys.J.Int.,2007,170:1195～1209
[18] Molnar P,Tapponnier P.Active tectonics of Tibet.J.Geophys.Res,1978,83(B1l):5361～5375
[19] Harrison T M,Copeland P,Kidd W S F,Yin A.Raising Tibet.Science,1992,255:1663～1670
[20] Molnar P,England P,Martinod J.Mantle dynamics,uplift of the Tibetan Plateau,and the India monsoon.Rev.Geophy.,1993,31:357～396
[21] Mercier J L,Armijo R,Tapponnier P,et al.Change from Tertiary compression to Quaternary extension in southern Tibet during the India Asia collision.Tectonics,1987,6:275～304
[22] Molnar P,Tapponnier P.Cenozoic tectonics of Asia:effects of a continental collision.Science,1975,183:419～426
[23] Molnar P,Chen W P.Focal depths and fault plane solutions of earthquakes under the Tibetan plateau.J.Geophys.Res.,1983,88:1180～1196
[24] He J,Lu S,Wang X.Mechanical relation between crustal rheology,effective fault friction,and strike-slip distribution among the Xiaojiang fault system,southeastern Tibet.Journal of Asian Earth Sciences,2009,34,363～375
[25] He J,Cherry J.late Quaternary slip rates of the Altyn Tagh,the Kunlun and Karakorum faults(Tibet)from 3D mechanical modeling.Earth Planet.Sci.Lett.,2008,274:50～58
[26] Liu M,Yang Y.The collapse of Tibetan plateau:Insights from 3-D finite element modeling.J.Geophys.Res.,2003,108(B8) ,2361,doi:10． 1029/2002JB002248
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