中国大陆壳幔运动耦合作用分析
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摘要
板块运动是地壳和上地幔变形的主要动力来源之一。因为只有地壳变形能被直接观测到,所以将上地壳变形场与下地壳和上地幔变形场比较是研究壳幔运动耦合作用的主要方法之一。利用中国大陆GPS观测结果,结合第四纪活动断层和由20世纪以来发生的地震资料反演获得的地球表层的水平应变率场,并将相关结果与Pn波各向异性及剪切波分裂的快波方向相比较,探讨中国大陆壳幔运动耦合作用。结果发现,总体来看活动性强的构造单元,其深部上地幔塑性剪切带的展布与上地壳脆性剪切带的方位有较大的差异;反之,活动性弱的构造单元,差异较小。活动构造单元其上地壳与下地壳—上地幔之间构造变形活动差异较大的原因,可能是在这个部位上、下地壳之间构造活动有一定程度的解耦,使下地壳以上部分的活动与其下“大地幔流”的运动趋势发生差异,从而产生构造应变能积累。
Plate motion is one of the major dynamic sources for crustal and mantle deformation. As crustal deformation can be measured by GPS and geologic observation, the comparison between crustal deformation and mantle deformation is an effective approach to understanding the coupling relationship between the crustal movement and the mantle deformation. In this study, regional crustal strain rate tensors for China inferred from GPS measurements, slip rates of Quaternary active fault and earthquake deformation data within an area of approximately 200×200 km 2 , are incorporated with smooth, continuous functions (sp line) to determine the self consistent model of present day velocity gradient tensor field for Chinas continent. In the incorporation process, GPS velocity vectors are also matched, within a defined frame of reference, with the model velocity field. The results are then compared with the anisotropy of the Pn wave and with the fast directions of shear wave splitting inferred from the SKS phases, which may represent the shear deformation in the mantle and the deep crust, respectively. The comparison shows that there is relatively large difference between the average directions of crustal shearing and that of mantle shearing in the regions of active tectonics. This may indicate the decoupling of crustal movement and mantle deformation in these active regions.
Plate motion is one of the major dynamic sources for crustal and mantle deformation. As crustal deformation can be measured by GPS and geologic observation, the comparison between crustal deformation and mantle deformation is an effective approach to understanding the coupling relationship between the crustal movement and the mantle deformation. In this study, regional crustal strain rate tensors for China inferred from GPS measurements, slip rates of Quaternary active fault and earthquake deformation data within an area of approximately 200×200 km 2 , are incorporated with smooth, continuous functions (sp line) to determine the self consistent model of present day velocity gradient tensor field for Chinas continent. In the incorporation process, GPS velocity vectors are also matched, within a defined frame of reference, with the model velocity field. The results are then compared with the anisotropy of the Pn wave and with the fast directions of shear wave splitting inferred from the SKS phases, which may represent the shear deformation in the mantle and the deep crust, respectively. The comparison shows that there is relatively large difference between the average directions of crustal shearing and that of mantle shearing in the regions of active tectonics. This may indicate the decoupling of crustal movement and mantle deformation in these active regions.
引文
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RENJin wei.2002.DeformationkinematicsofChinamainlanddeterminedfromGPSobservations[J].ChineseJournalofGeophysics,45(suppl):123—135(inChinese).
汪素云,许忠淮,裴顺平.2003.中国大陆Pn波速度结构与强震孕育的深部背景[J].地球物理学报,46(6):123—135.
WANGSu yun,XUZhong huai,PEIShun ping.2003.PnvelocityvariationbeneathChinamainlandanddeepstructurebackgroundformajorearthquakegeneration[J].ChineseJournalofGeophysics,46(6):123—135(inChinese).
张培震,邓起东,张国民,等.2003.中国大陆的强震活动与活动地块[J].中国科学(D辑),33(增刊):12—20.
ZHANGPei zhen,DENGQi dong,ZHANGGuo min,etal.2003.ContinentalearthquakesandactiveblocksinChina[J].ScienceinChina(SerD),33(suppl):12—20(inChinese).
ArgusDF ,GordonRG .1991.No net rotationmodelofcurrentplatevelocitiesincorporatingplatemotionmodelNUVEL 1[J].GeophysResLett,18:2039—2042.
ChenWP ,OzalaybeyS .1998.CorrelationbetweenseismicanisotropyandBouguergravityanomaliesinTibetanditsimpli cationsforlithosphericstructures[J].GeophysJourInt,135:93—101.
DavisP ,EnglandP ,HousemanG .1997.ComparisonofshearwavesplittingandfinitestrainfromtheIndiaAsiacollisionzone[J].JourGeophysRes,102:27511—27522.
DeMetsC ,GordonRG ,ArgusDF ,etal.1994.Effectofrecentrevisiontothegeomagneticreversaltimescaleonestimatesofcurrentplatemotion[J].GeophysResLett,21:2191—2194.
HirnA ,JiangM ,SapinM ,etal.1995.SeismicanisotropyasanindicatorofmantleflowbeneaththeHimalayasandTibet[J].Nature,375:571—574.
HainesAJ ,JacksonJA ,HoltWE ,etal.1998.Representingdistributeddeformationbycontinuousvelocityfields[J].ScienceReport,May1998,InstituteofGeologyandNuclearSciences,Wellington,NewZealand.
HoltEW ,ChamotRookeN ,LePichonX ,etal.2000.VelocityfieldinAsiainferredfromQuaternaryfaultslipratesandGlobalPositioningSystemobservations[J].JourGeophysRes,105:19185—19209.
HoltWE ,HainesAJ .1993.VelocityfieldsindeformingAsiafromtheinversionofearthquake releasedstrains[J].Tec tonics,12:1—20.
MainpriceD ,SilverPG .1993.InterpretationofSKSwaveusingsamplesfromthesubcontinentallithosphere[J].PhysEarthPlanetSci,78:257—280.
McNamaraDE ,OwensTJ,SilverPG ,etal.1994.ShearwaveanisotropybeneaththeTibetanPlateau[J].JourGeophysRes,99:13655—13665.
NelsonKD ,ZhaoW ,BrownLD ,etal.1996.PartiallymoltenmiddlecrustbeneathsouthernTibet:SynthesisofProjectINDEPTHresults[J].Science,274:1684—1688.
PlomerovaJ,SilenyJ,BabuskaV .1996.Jointinterpretationofupper mantleanisotropybasedonteleseismicP traveltimedelaysandinversionofshear wavesplittingparameters[J].PhysEarthPlanetInt,95:293—309.
SandovalE ,NiJ ,KindR ,etal.1997.SeismicanisotropybeneaththesouthernHimalayasTibetcollisionzone[J].JourGeopysRes,102:17813—17823.
SilverPG ,ChanWW .1991.Shear wavesplittingandsubcontinentalmantledeformation[J].JourGeophysRes,96:16429—16454.
SilverPG .1996.Seismicanisotropybeneaththecontinents:Probingthedepthsofgeology[J].JourAnnuRevEarthPlanetSci,24:385—432.
VauchezA ,BarruolG .1996.Shear wavesplittingintheAppalachiansandthePyrenees:Importanceoftheinheritedtectonicfabricofthelithosphere[J].PhysEarthPlanetInt,95:127—138.
VinnikLP ,GreenRWE ,NicolaysenLO .1995.RecentdeformationofthedeepcontinentalrootbeneathSouthAfrica[J].Nature,375:50—52.
ZhangS ,KaratoSL .1995.Latticepreferredorientationofolivineaggregatesdeformation[J].Nature,375:774—777.
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