根据GPS和InSAR数据反演2001年昆仑山口西地震同震破裂分布
摘要
2001年昆仑山口西地震经历了一个相当复杂的破裂过程,迄今为止用不同资料、不同方法和模型得到的同震破裂发布具有很大差异.我们采用地震前后GPS和InSAR观测数据得到的同震位移反演该地震的同震破裂分布。检验各种可能的模型参数,得到在数据与平滑优化约束下尽可能详尽的结果.建模过程经历三个步骤:(1)采用直立断层模型反演.根据解的分辨率和拟合差的折中曲线得到最优平滑约束;(2)改变断层倾角,找到使得观测数据和正演计算拟合最好的断层倾角;(3)根据前面两步得到的最优平滑约束和断层倾角求得地震同震破裂分布.比起前人的研究结果,我们得到的地表走滑分量随断层分布与地质考察数据符合得更好.我们还发现形变沿断层两盘并不对称.断层南盘的位移比北盘大10%～20%.这种位移场的不对称性可以由倾角约为80°～81°的南倾断层所解释.我们首次用大地测量数据揭示了太阳湖断层东端和东昆仑主断层西端～50 km的左阶断层上吸收了0.1～0.2 m的正断层分量,昆仑山口断层段吸收了～0.8 m的逆冲分量.地震释放的总地震矩为9.3×10~(20)N·m,对应于M_w8.0的地震.
The rupture process of the 2001 Ms 8.1 Kunlun Mountain Pass west earthquake was quite complex.Studies on its coseismic rupture distribution using different datasets,methods, and models have so far produced rather different results.We use coseismic displacement data obtained from the Global Positioning System(GPS)and Interferometric Synthetic Aperture Radar(InSAR)measurements made before and after the earthquake to invert for its rupture distribution.We test multiple model parameters,and provide a more detailed result than previous studies under an optimized smoothing constraint.The modeling process consists of three steps: First,assuming a vertical fault plane we obtain an optimal smoothing constraint for the solution based on balancing a trade-off between the solution resolution and model misfit.Second,we vary dipping angles of fault segments to search for optimal dipping angles in data fitting.Finally,we adopt the fault smoothing constraint and dipping angles obtained from previous two steps and invert for the coseismic rupture distribution.Comparing with previous studies,our results agree better with the field survey results on horizontal surface offsets.We also find that the coseismic displacement amplitudes are asymmetric across the seismic fault,with the displacements south of the fault about 10%～20% larger in amplitude than that north of the fault.This observation can be explained by the fault dipping 80°～81°to the south.We also demonstrate the first time that a left step of about 50 km length located between the west end of the rupture on the East Kunlun fault and the east end of the Sun Lake fault absorbed 0.1～0.2 m of normal faulting,and the Kunlun Pass fault absorbed about 0.8 m thrust faulting.The seismic moment release is estimated 9.3×10~(20)N·m,corresponding to a M_w 8.0 earthquake.
The rupture process of the 2001 Ms 8.1 Kunlun Mountain Pass west earthquake was quite complex.Studies on its coseismic rupture distribution using different datasets,methods, and models have so far produced rather different results.We use coseismic displacement data obtained from the Global Positioning System(GPS)and Interferometric Synthetic Aperture Radar(InSAR)measurements made before and after the earthquake to invert for its rupture distribution.We test multiple model parameters,and provide a more detailed result than previous studies under an optimized smoothing constraint.The modeling process consists of three steps: First,assuming a vertical fault plane we obtain an optimal smoothing constraint for the solution based on balancing a trade-off between the solution resolution and model misfit.Second,we vary dipping angles of fault segments to search for optimal dipping angles in data fitting.Finally,we adopt the fault smoothing constraint and dipping angles obtained from previous two steps and invert for the coseismic rupture distribution.Comparing with previous studies,our results agree better with the field survey results on horizontal surface offsets.We also find that the coseismic displacement amplitudes are asymmetric across the seismic fault,with the displacements south of the fault about 10%～20% larger in amplitude than that north of the fault.This observation can be explained by the fault dipping 80°～81°to the south.We also demonstrate the first time that a left step of about 50 km length located between the west end of the rupture on the East Kunlun fault and the east end of the Sun Lake fault absorbed 0.1～0.2 m of normal faulting,and the Kunlun Pass fault absorbed about 0.8 m thrust faulting.The seismic moment release is estimated 9.3×10~(20)N·m,corresponding to a M_w 8.0 earthquake.
引文
[1]中国地震局监测预报司．2001年昆仑山口西8．1级大地震．北京：地震出版社，2002．1～129 Department of Earthquake Monitoring and Prediction,CEA. The 2001 Ms8.1 large earthquake,west of the Kunlun Pass (in Chinese).Beijing:Seismological Press,2002.129
[2]Van der Woerd J,Ryerson FJ,Tapponnier P,et al.Uniform slip rate along the Kunlun fault:implications for seismic behavior and large-scale tectonics.Geophys.Res.Lett., 2000,27:2353～2356
[3]Van der Woerd J,Meriaux A S,Klinger Y,et al.The 14 November 2001,M_w=7.8 Kokoxili earthquake in northern Tibet(Qinghai Province,China).Seism.Res.Lett.,2002, 73(2),125～135
[4]青海省地震局、中国地震局地壳应力研究所．东昆仑活动断裂带．北京：地震出版社，1999．1～186 Qinghai Seismological Bureau and Institute of Crustal Dynamics,China Seismological Bureau.Eastern Kunlun Active Fault Zone(in Chinese).Beijing:Seismological Press, 1999.1～186
[5]沈正康，万永革，甘卫军等．东昆仑活动断裂带大地震之间的黏弹性应力触发研究．地球物理学报，2003，46(6)：786～795 Shen Z K,Wan Y G,Gun W J,et al.Viscoelastic triggering among large earthquakes along the east Kunlun fault system. Chinese J.Geophys.(in Chinese),2003,46(6):787～796
[6]Xu X,Chen W,Ma W,et al.Surface rupture of the Kunlunshan earthquake(M_s 8.1),northern Tibetan plateau, China.Seismol.Res.Lett.,2002,73:884～892
[7]Lin A,Fu B,Guo J,et al.Co-seismic strike-slip and rupture length produced by the 2001 M,8.1 Central Kunlun Earthquake.Science,2002,296:2015～2017
[8]陈杰，陈宇坤，丁国瑜等．2001年昆仑山口西8．1级地震地表破裂带．第四纪研究．2003，23(6)：629～639 Chen J,Chen Y K,Ding G Y,et al.Surface rupture zones of the 2001 earthquake M,8.1 west of Kunlun Pass,Northern Qinghai-Xizang Plateau.Quaternary Sciences(in Chinese), 2003,23(6):629～639
[9]Xu X,Yu G,Kinger Y,et al.Reevaluation of surface parameters and faulting segmentation of the 2001 Kunlunshan earthquake(Mw7.8),northern Tibetan Plateau,China.J Geophys Res,2006,111:1305316,doi;10.1029/ 2004JB003488
[10]任金卫，王敏．GPS观测的2001年昆仑山口西Ms8．1级地震地壳变形．第四纪研究，2005，25(1)：34～44 Ren J W,Wang M.GPS measured crustal deformation of the Ms8.1 Kunlun earthquake on november 14th 2001 in Qinghai-Xizang plateau.Quaternary Sciences(in Chinese), 2005,25(i):34～44
[11]乔学军，王琪，杜瑞林等．昆仑山口西M_s 8．1地震的地壳变形特征．大地测量与地球动力学，2002，22(4)：6～11 Qiao X J,Wang Q,Du R L,et al.Characteristics of crustal deformation relating to M_s8.1 Kunlunshan earthquake. Journal of Geodesy and Geodynamics(in Chinese),2002,22 (4),6～11
[12]万永革，王敏，沈正康等．利用GPS和水准测量资料反演2001年昆仑山口西8．1级地震的同震滑动分布．地震地质，2004，26(3)：393～404 Wan Y G,Wang M,Shen Z K,et al.Co-seismic slip distribution of the 2001 west of Kunlun Mountain Pass earthquake inverted by GPS and leveling data.Seismology and Geology(in Chinese),2004,26(3):393～404
[13]单新建，柳家航，马超．2001年昆仑山口西8．1级地震同震形变场特征的初步分析．地震学报，2004，26(5)：474～480 Shah X,Liu J,Ma C.Preliminary analysis on characteristics of coseismic deformation associated with M_s=8.1 western Kunlunshan Pass earthquake in 2001.Acta Seismologica Sicina,2004,17:526～533
[14]马超，单新建．昆仑山M_s8．1地震震源参数的多破裂段模拟研究．地球物理学报．2006，49(2)：428～437 Ma C,Shah X J.A multi-segment analytic modeling of hypocentral geometric characteristic parameters of the M_s 8.1 earthquake at the Kunlun Mountains.Chinese J.Geophys.( in Chinese),2006,49(2):428～437
[15]Lasserre C,Peltzer G,Cramp F,et al.Coseismie deformation of the Mw=7.8 Kokoxili earthquake in Tibet, measured by synthetic aperature radar interferometry.J. Geophys.Res.,2005,I10:B12408,doi:10.1029/ 2004JB003500
[16]许力生，陈运泰．从长周期波形资料反演2001年11月14日昆仑山口地震时空破裂过程．中国科学(D辑)，2004，34(3)：256～264 Xu L S,Chen Y T.Temporal and spatial rupture process of the great Kunlun maintain pass earthquake of Nov.14, 2001,from GDSN long period waveform data.Science in China(D)(in Chinese),2004,34(3):256～264
[17]Lin A,Kikuchi M,Fu B.Rupture segmentation and process of the 2001 M_w 7.8 central Kunlun,China,earthquake. Bull.Seism.Soc.Amer.,2003,93:2477～2492
[18]Bouchon M,Vallee M.Observation of long supershear rupture during the M_s=8.1 Kunlunshan(Tibet) earthquake.Science,2003,301:824～826
[19]Antolik M,Abererombie R E,Ekstrom G.The 14 November 2001 Kokoxili(Kunlunshan),Tibet,earthquake: Rupture transfer through a large extensional step-over.Bull. Seismol.Soc.Amer.,2004,94(4):1173～1194
[20]Ozacar A A,Beck S L.The 2002 Denali fault and 2001 Kunlun fault earthquakes:Complex rupture process of two large strike-slip events.Bull.Seism.Soc.Amer.,2004, 94:278～292
[21]Tocheport A,Rivera L,Van der Woerd J.A study of the 14 November 2001 Kokoxili earthquake.,history and geometry of the rupture from teleseismic data and field observations. Bull Seismol Soc Amer,2006,96(5):1729～1741
[22]Shen Z K,Wang M,Li Y,et al.Crustal deformation associated with the Altyn Tagh fault system,western China, from GPS.J.Geophys.Res.,2001,106(B12):30607～30621
[23]王敏，沈正康，牛之俊等．现今中国大陆地壳运动与活动块体模型．中国科学(D辑)，2003，46(S1)：21～32 Wang M,Shen Z K,Niu g J,et al.Contemporary crustal deformation of the Chinese continent and tectonic block model.Science in China(D)(in Chinese),2003,46(Suppl): 25～40
[24]党光明，王赞军．青海昆仑山口西M_s8．1级地震地表破裂带特征与主要震害——对青藏高原区域稳定性评价的制约．地质通报，2002，21(2)：105～120 Dang G M,Wang Z J.Characteristics of the surface rupture zone and main seismic hazards caused by the M_s8.1 earthquake west of Kunlun pass,China——constraints on the regional stability of the Qinghai-Tibet plateau.Geological Bulletin of China(in Chinese),2002,21(2):105～108
[25]Klinger Y,Xu X,Tapponnier P,et al.High-resolution satellite imagery mapping of the surface rupture and slip distribution of the M_w～7.8,14 November 2001 Kokoxili earthquake,Kunlun fault,northern Tibet,China.Ball. Seismol.Soc.Amer.,2005,95(5):1970～1987
[26]Klinger Y,Michel R,King G C P,et al.Evidence for an earthquake harrier model from M_w7.8 Kokoxili(Tibet) earthquake slip-distribution.Earth and Planetary Science Letters,2006,242:354～364
[27]Jackson D D.The use of a priori data to resolve the non- uniqueness in linear inversion.Geophys.J.R.Astr.Soc., 1979,57:137～157
[28]Jackson D D,Matsu'ura M.A Bayesian approach to nonlinear inversion.J.Geophys.Res.,1985,90:581～591
[29]Shen Z K,Ge X B,Jackson D D,et al.Northridge earthquake rupture model based on Global Positioning System measurements.Bull.Seism.Soc.Amer.,1996,86(1B): 37～48
[30]Okada Y.Internal deformation due to shear and tensile faults in a half-space.Bull.Seisra.Soc.Amer.,1992,82:1018～1040
[31]陶玮，沈正康，万永革等．根据2001年M_w 7．8可可西里强震InSAR同震测量结果反演东昆仑断裂两侧地壳弹性介质差异．地球物理学报，2007，50(3)；90～97 Tao W,Shen Z K,Wan Y G,et al.Crustal elasticity contrast across the East Kunlun fault in Northern Tibet, inferred from InSAR measurements of the 2001 M_w 7.8 Kokoxili earthquake.Chinese J.Geophys.(in Chinese), 2007,50(3):90～97
[2]Van der Woerd J,Ryerson FJ,Tapponnier P,et al.Uniform slip rate along the Kunlun fault:implications for seismic behavior and large-scale tectonics.Geophys.Res.Lett., 2000,27:2353～2356
[3]Van der Woerd J,Meriaux A S,Klinger Y,et al.The 14 November 2001,M_w=7.8 Kokoxili earthquake in northern Tibet(Qinghai Province,China).Seism.Res.Lett.,2002, 73(2),125～135
[4]青海省地震局、中国地震局地壳应力研究所．东昆仑活动断裂带．北京：地震出版社，1999．1～186 Qinghai Seismological Bureau and Institute of Crustal Dynamics,China Seismological Bureau.Eastern Kunlun Active Fault Zone(in Chinese).Beijing:Seismological Press, 1999.1～186
[5]沈正康，万永革，甘卫军等．东昆仑活动断裂带大地震之间的黏弹性应力触发研究．地球物理学报，2003，46(6)：786～795 Shen Z K,Wan Y G,Gun W J,et al.Viscoelastic triggering among large earthquakes along the east Kunlun fault system. Chinese J.Geophys.(in Chinese),2003,46(6):787～796
[6]Xu X,Chen W,Ma W,et al.Surface rupture of the Kunlunshan earthquake(M_s 8.1),northern Tibetan plateau, China.Seismol.Res.Lett.,2002,73:884～892
[7]Lin A,Fu B,Guo J,et al.Co-seismic strike-slip and rupture length produced by the 2001 M,8.1 Central Kunlun Earthquake.Science,2002,296:2015～2017
[8]陈杰，陈宇坤，丁国瑜等．2001年昆仑山口西8．1级地震地表破裂带．第四纪研究．2003，23(6)：629～639 Chen J,Chen Y K,Ding G Y,et al.Surface rupture zones of the 2001 earthquake M,8.1 west of Kunlun Pass,Northern Qinghai-Xizang Plateau.Quaternary Sciences(in Chinese), 2003,23(6):629～639
[9]Xu X,Yu G,Kinger Y,et al.Reevaluation of surface parameters and faulting segmentation of the 2001 Kunlunshan earthquake(Mw7.8),northern Tibetan Plateau,China.J Geophys Res,2006,111:1305316,doi;10.1029/ 2004JB003488
[10]任金卫，王敏．GPS观测的2001年昆仑山口西Ms8．1级地震地壳变形．第四纪研究，2005，25(1)：34～44 Ren J W,Wang M.GPS measured crustal deformation of the Ms8.1 Kunlun earthquake on november 14th 2001 in Qinghai-Xizang plateau.Quaternary Sciences(in Chinese), 2005,25(i):34～44
[11]乔学军，王琪，杜瑞林等．昆仑山口西M_s 8．1地震的地壳变形特征．大地测量与地球动力学，2002，22(4)：6～11 Qiao X J,Wang Q,Du R L,et al.Characteristics of crustal deformation relating to M_s8.1 Kunlunshan earthquake. Journal of Geodesy and Geodynamics(in Chinese),2002,22 (4),6～11
[12]万永革，王敏，沈正康等．利用GPS和水准测量资料反演2001年昆仑山口西8．1级地震的同震滑动分布．地震地质，2004，26(3)：393～404 Wan Y G,Wang M,Shen Z K,et al.Co-seismic slip distribution of the 2001 west of Kunlun Mountain Pass earthquake inverted by GPS and leveling data.Seismology and Geology(in Chinese),2004,26(3):393～404
[13]单新建，柳家航，马超．2001年昆仑山口西8．1级地震同震形变场特征的初步分析．地震学报，2004，26(5)：474～480 Shah X,Liu J,Ma C.Preliminary analysis on characteristics of coseismic deformation associated with M_s=8.1 western Kunlunshan Pass earthquake in 2001.Acta Seismologica Sicina,2004,17:526～533
[14]马超，单新建．昆仑山M_s8．1地震震源参数的多破裂段模拟研究．地球物理学报．2006，49(2)：428～437 Ma C,Shah X J.A multi-segment analytic modeling of hypocentral geometric characteristic parameters of the M_s 8.1 earthquake at the Kunlun Mountains.Chinese J.Geophys.( in Chinese),2006,49(2):428～437
[15]Lasserre C,Peltzer G,Cramp F,et al.Coseismie deformation of the Mw=7.8 Kokoxili earthquake in Tibet, measured by synthetic aperature radar interferometry.J. Geophys.Res.,2005,I10:B12408,doi:10.1029/ 2004JB003500
[16]许力生，陈运泰．从长周期波形资料反演2001年11月14日昆仑山口地震时空破裂过程．中国科学(D辑)，2004，34(3)：256～264 Xu L S,Chen Y T.Temporal and spatial rupture process of the great Kunlun maintain pass earthquake of Nov.14, 2001,from GDSN long period waveform data.Science in China(D)(in Chinese),2004,34(3):256～264
[17]Lin A,Kikuchi M,Fu B.Rupture segmentation and process of the 2001 M_w 7.8 central Kunlun,China,earthquake. Bull.Seism.Soc.Amer.,2003,93:2477～2492
[18]Bouchon M,Vallee M.Observation of long supershear rupture during the M_s=8.1 Kunlunshan(Tibet) earthquake.Science,2003,301:824～826
[19]Antolik M,Abererombie R E,Ekstrom G.The 14 November 2001 Kokoxili(Kunlunshan),Tibet,earthquake: Rupture transfer through a large extensional step-over.Bull. Seismol.Soc.Amer.,2004,94(4):1173～1194
[20]Ozacar A A,Beck S L.The 2002 Denali fault and 2001 Kunlun fault earthquakes:Complex rupture process of two large strike-slip events.Bull.Seism.Soc.Amer.,2004, 94:278～292
[21]Tocheport A,Rivera L,Van der Woerd J.A study of the 14 November 2001 Kokoxili earthquake.,history and geometry of the rupture from teleseismic data and field observations. Bull Seismol Soc Amer,2006,96(5):1729～1741
[22]Shen Z K,Wang M,Li Y,et al.Crustal deformation associated with the Altyn Tagh fault system,western China, from GPS.J.Geophys.Res.,2001,106(B12):30607～30621
[23]王敏，沈正康，牛之俊等．现今中国大陆地壳运动与活动块体模型．中国科学(D辑)，2003，46(S1)：21～32 Wang M,Shen Z K,Niu g J,et al.Contemporary crustal deformation of the Chinese continent and tectonic block model.Science in China(D)(in Chinese),2003,46(Suppl): 25～40
[24]党光明，王赞军．青海昆仑山口西M_s8．1级地震地表破裂带特征与主要震害——对青藏高原区域稳定性评价的制约．地质通报，2002，21(2)：105～120 Dang G M,Wang Z J.Characteristics of the surface rupture zone and main seismic hazards caused by the M_s8.1 earthquake west of Kunlun pass,China——constraints on the regional stability of the Qinghai-Tibet plateau.Geological Bulletin of China(in Chinese),2002,21(2):105～108
[25]Klinger Y,Xu X,Tapponnier P,et al.High-resolution satellite imagery mapping of the surface rupture and slip distribution of the M_w～7.8,14 November 2001 Kokoxili earthquake,Kunlun fault,northern Tibet,China.Ball. Seismol.Soc.Amer.,2005,95(5):1970～1987
[26]Klinger Y,Michel R,King G C P,et al.Evidence for an earthquake harrier model from M_w7.8 Kokoxili(Tibet) earthquake slip-distribution.Earth and Planetary Science Letters,2006,242:354～364
[27]Jackson D D.The use of a priori data to resolve the non- uniqueness in linear inversion.Geophys.J.R.Astr.Soc., 1979,57:137～157
[28]Jackson D D,Matsu'ura M.A Bayesian approach to nonlinear inversion.J.Geophys.Res.,1985,90:581～591
[29]Shen Z K,Ge X B,Jackson D D,et al.Northridge earthquake rupture model based on Global Positioning System measurements.Bull.Seism.Soc.Amer.,1996,86(1B): 37～48
[30]Okada Y.Internal deformation due to shear and tensile faults in a half-space.Bull.Seisra.Soc.Amer.,1992,82:1018～1040
[31]陶玮，沈正康，万永革等．根据2001年M_w 7．8可可西里强震InSAR同震测量结果反演东昆仑断裂两侧地壳弹性介质差异．地球物理学报，2007，50(3)；90～97 Tao W,Shen Z K,Wan Y G,et al.Crustal elasticity contrast across the East Kunlun fault in Northern Tibet, inferred from InSAR measurements of the 2001 M_w 7.8 Kokoxili earthquake.Chinese J.Geophys.(in Chinese), 2007,50(3):90～97
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