喜马拉雅地区S波分裂研究
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摘要
利用最小特征值法,分析了喜马拉雅地区56个台站的地震记录,其中有39个台站能观察到S波分裂,其平均分裂时间在0.8 s左右.沿台站GAIG-T0040连线的东西两侧各向异性参数呈现明显的差别:其以西地区,约有一半的台站没有观测到S波分裂,快波方向主要为NW和NWW方向;以东地区台站的快波方向在MBT(主边界断裂)以南为NNE向,平均分裂时间为1.05 s;低喜马拉雅地区为NE和NEE向,平均分裂时间为0.72 s;而在特提斯喜马拉雅地区为N-S和NNE向,平均分裂时间为0.68 s.综合其他研究结果,认为东西向各向异性参数的差异是由于印度块体向北推进时的横向不均匀性造成的,而南北向的变化与该地区构造单元的分布一致.
The records of 56 stations in Himalaya area were analyzed by using the method of minimizing the eigenvalue.Shear wave splitting was observed in thirty-nine stations of them.The average splitting time is about 0.8s.The parameters of splitting are not only different from south to north,but also different either side of the line joining the stations GAIG and T0040(AA′).To the west of the line,FPD(fast polarization direction) is mainly in the NWW or NW direction.To the east of it,FPD is in NNE to the south of MBT.FPD is NE or NEE in Lesser Himalaya and it becomes N-S or NEE in Tethys Himalaya.Comparing with other studies,we argue that the difference of splitting parameters between east and west is produced by lateral heterogeneous collision between Indian plate and Eurasia plate.The variation from south to north to the east of AA′ is produced by the complicated structure in this area.
The records of 56 stations in Himalaya area were analyzed by using the method of minimizing the eigenvalue.Shear wave splitting was observed in thirty-nine stations of them.The average splitting time is about 0.8s.The parameters of splitting are not only different from south to north,but also different either side of the line joining the stations GAIG and T0040(AA′).To the west of the line,FPD(fast polarization direction) is mainly in the NWW or NW direction.To the east of it,FPD is in NNE to the south of MBT.FPD is NE or NEE in Lesser Himalaya and it becomes N-S or NEE in Tethys Himalaya.Comparing with other studies,we argue that the difference of splitting parameters between east and west is produced by lateral heterogeneous collision between Indian plate and Eurasia plate.The variation from south to north to the east of AA′ is produced by the complicated structure in this area.
引文
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[34]张进,马宗晋.西藏高原西、中、东的分段性及其意义.地质学报,2004,78(2):218~227Zhang J,Ma Z J.East-west segmentation of the Tibetan Plateau andits implication.Acta Geologica Sinica(in Chinese),2004,78(2):218~227
[35]Pandy O P.Lithospheric mantle deformation beneath the Indiancratons.Journal of Geology,1999,107:683~692
[36]Ribe N M,Yu Y.On the relationship between seismic anisotropy andfinite strain.J.Geophys.Res.,1992,97:8737~8747
[37]Anderson.Theory of the Earth.Blackwell Scientific Publications,Boston,1989
[38]赵文津,薛光琦,吴珍汉等.西藏高原上地幔的精细结构与构造——地震层析成像给出的启示.地球物理学报,2004,47(3):449~455Zhao W J,Xue G Q,Wu Z H,et al.Fine velocity structure of theupper mantle beneath the Xizang plateau from tomography and itsgeological interpretations.Chinese J.Geophys.(in Chinese),2004,47(3):449~455
[39]Wang Q,Zhang P Z,Freymueller J T,et al.Present-day crustaldeformation in China constrained by Global Positioning Systemmeasurements.Science,2001,294:574~577
[2]Silver P G.Seismic anisotropy beneath the continents:probing thedepths of geology.Annu.Rev.Earth.Planet.Sci.,1996,24:385~432
[3]Vinnik L P,Makeyeva L,Milev A,et al.Global patterns of azimuthalanisotropy and deformation in the continental mantle.Geophys.J.Int.,1992,111:433~447
[4]Silver P G,Chan W.Shear wave splitting and mantle deformation.J.Geophys.Res,1991,96:16429~16454
[5]Levin V,Menke W,Park J.Shear wave splitting in the Appalachiansand Urals:a case for multilayered anisotropy.J.Geophys.Res.,1999,104:17975~17993
[6]Crampin S.A review of wave motion in anisotropic and crackedelastic-media.Wave Motion,1981,3:343~391
[7]Savage M K.Seismic anisotropy and mantle deformation:What havewe learned from shear wave splitting?Reviews of Geophysics,1999,37:65~106
[8]曾融生,吴大铭,Owens T J.中美合作课题“青藏高原地壳上地幔结构以及地球动力学的研究”介绍.地震学报,1992,14(增刊):521~522Zeng R S,Wu D M,Owens T J.An introduction to the Sino-US jointproject“Lithospheric structure and dynamics in Tibetan Plateau”.Acta Seismologica Siniea(in Chinese),1992,14(Suppl.):521~522
[9]Schulte-Pelkuml V G,Monsalve G,Sheehan A,et al.Imaging theIndian subcontinent beneath the Himalaya.Nature,2005,435:1222~1225
[10]Herquel G,Wittlinger G,Guibert J.Anisotropy and crustal thicknessof Northern-Tibet.New Constraints for tectonic modeling.Geophys.Res.Lett.,1995,22:1925~1928
[11]Vergne J,Wittlinger G,Farra V,et al.Evidence for upper crustalanisotropy in the Songpan-Ganze(northeastern Tibet)terrane.Geophys.Res.Lett.,2003,30,1552,doi:10.1029/2002GL016847
[12]McNamara D E,Owens T J,Silver P G,et al.Shear wave anisotropybeneath the Tibetan Plateau.J.Geophys.Res.,1994,99:13655~13665
[13]Hirn A,Jiang M,Spain M,et a1.Seismic anisotropy as an indicator ofmantle flow beneath Himalayas and Tibet.Nature,1995,375:571~574
[14]Herquel G,Tapponnier P.Seismic anisotropy in western Tibet.Geophys.Res.Lett.,2005,32,L17306,doi:10.1029/2005GL023561
[15]Sandvol E,Ni J F,Hearn T M,et al.Seismic anisotropy beneath thePakistan Himalayas.Geophys.Res.Lett.,1994,21:1635~1638
[16]Sandvol E,Ni J,Kind R,et al.Seismic anisotropy beneath thesouthern Himalaya Tibet collision zone.J.Geophys.Res.,1997,102:17813~17823
[17]Huang W C,James F,Frederic T,et al.Seismic polarizationanisotropy beneath the central Tibetan Plateau.J.Geophys.Res.,2000,105:27979~27989
[18]丁志峰,曾融生.青藏高原横波分裂的观测研究.地球物理学报,1996,39(2):211~220Ding Z F,Zeng R S.Observation and study of shear wave anisotropyin Tibetan plateau.Chinese J.Geophys.(in Chinese),1996,39(2):211~220
[19]姜枚,许志琴,Hirn A等.青藏高原及部分邻区地震各向异性和上地幔特征.地球学报,2001,22(2):111~116Jiang M,Xu Z Q,Hirn A,et al.Teleseismic anisotropy andcorresponding features of the upper mantle in Tibet plateau and itsneighboring areas.Acta Geoscientia Sinica(in Chinese),2001,22(2):111~116
[20]史大年,董英君,姜枚等.西藏定日-青海格尔木上地幔各向异性研究.地质学报,1996,70(4):291~297Shi D N,Dong Y J,Jiang M,et al.Shear wave anisotropy of theupper mantle beneath the Tingri of Tibet to Golmud of Qinghai.ActaGeologica Sinica(in Chinese),1996,70(4):291~297
[21]吕庆田,马开义,姜枚等.青藏高原南部下的横波各向异性.地震学报,1996,18(2):215~223LüQ T,Ma K Y,Jiang M,et al.Seismic anisotropy of transversebeneath the Tibet Plateau.Acta Seismologica Sinica(in Chinese),1996,18(2):215~223
[22]郑斯华,高原.中国大陆岩石层的方位各向异性.地震学报,1994,16(2):131~140Zheng S H,Gao Y.Azimuth anisotropy of lithosphere of continental.Acta Seismologica Sinica(in Chinese),1994,16(2):131~140
[23]Liu K,Zhang Z J,Hu J F,et al.Frequency band-dependence of S-wave splitting in China mainland and its implications.Science inChina(Series D),2001,44:659~665
[24]Chen W P,Ozalaybey S.Correlation between seismic anisotropy andBouguer gravity anomalies in Tibet and its implications for lithosphericstructures.Geophys.J.Int.,1998,135:93~101
[25]Yin A,Harrision T M.Geologic evolution of the Himalayan-Tibetanorogen.Annu.Rev.Earth Planet.Sci.,2000,28:211~280
[26]Torre T L,Sheehan A F.Broadband seismic noise analysis of theHimalayan Nepal Tibet seismic experiment.Bull.Seismol.Soc.Am.,2005,95:1202~1208
[27]高名修.青藏高原南缘现今地球动力学研究.地震地质,1996,18(2):144~155Gao M X.A study on recent geodynamics at the southern margin ofthe Qinghai-Xizang(Tibet)plateau.Seismology and Geology(inChinese),1996,18(2):144~155
[28]Ramesh D S,Bhartur R N,Prakasan K S,et al.Predominance ofplate motion-related strain in the south Indian shield.Current.Sci.,1996,70:843~847
[29]Pandey M R,Tandukar R P,Avouacb J P,et al.Seismotectonics ofthe Nepal Himalaya from a local seismic network.J.Asian EarthSci.,1999,17:703~712
[30]Kapp P,Guynn J H.Indian punch rifts Tibet.Geology,2004,32:993~996
[31]Monsalve G,Sheehan A F.Seismicity and 3-D velocity structure ofthe Himalayan collision zone:Lateral variations in lithosphericstructure.Eos Trans AGU,86(52),Fall Meet.Suppl.,AbstractT52A-07
[32]周华伟,Michael A M,林清良.西藏及其周围地区地壳、地幔地震层析成像-印度板块大规模俯冲于西藏高原之下的证据.地学前缘,2002,9(4):285~292Zhou H W,Michael A M,Lin Q L.Tomographic imaging of the Tibetand surrounding region:Evidence for wholesale underthrusting ofIndian slab beneath the Tibetan Plateau.Earth Science Frontiers(inChinese),2002,9(4):285~292
[33]Zhang Z,Teng J,Li Y,et al.Crustal structure of seismic velocity inthe southern Tibet and east-westward escape of the crustalmaterial———An example by wide-angle seismic profile from Peigu Tsoto Pumoyong Tso.Science in China(Ser.D),2004,47:500~506
[34]张进,马宗晋.西藏高原西、中、东的分段性及其意义.地质学报,2004,78(2):218~227Zhang J,Ma Z J.East-west segmentation of the Tibetan Plateau andits implication.Acta Geologica Sinica(in Chinese),2004,78(2):218~227
[35]Pandy O P.Lithospheric mantle deformation beneath the Indiancratons.Journal of Geology,1999,107:683~692
[36]Ribe N M,Yu Y.On the relationship between seismic anisotropy andfinite strain.J.Geophys.Res.,1992,97:8737~8747
[37]Anderson.Theory of the Earth.Blackwell Scientific Publications,Boston,1989
[38]赵文津,薛光琦,吴珍汉等.西藏高原上地幔的精细结构与构造——地震层析成像给出的启示.地球物理学报,2004,47(3):449~455Zhao W J,Xue G Q,Wu Z H,et al.Fine velocity structure of theupper mantle beneath the Xizang plateau from tomography and itsgeological interpretations.Chinese J.Geophys.(in Chinese),2004,47(3):449~455
[39]Wang Q,Zhang P Z,Freymueller J T,et al.Present-day crustaldeformation in China constrained by Global Positioning Systemmeasurements.Science,2001,294:574~577
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