利用地震层析成像数据计算地幔对流新模型的探讨
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摘要
假设地幔地震层析成像数据对应的地幔横向不均匀结构是地幔热对流的结果 .将地震层析成像数据转化为地幔温度 (或密度 )不均匀分布 ,考虑热流体动力学的三个基本方程 ,顾及热输运方程中的非线性项 ,直接将地震层析成像转化的地幔温度不均匀分布作为内部荷载引入基本方程 ,反演计算地幔对流 .本文在利用地震层析成像数据计算地幔对流模型的新理论和方法的基础上 ,用SH12WM13地震层析成像模型数据 ,计算了全球地幔对流格局 .结果表明 ,对流格局不仅依赖地震层析成像数据 ,而且在很大程度上受地幔动力学框架、热动力参数和边界条件的所确定的系统响应函数的影响 .显示了地幔中复杂的对流格局 ,特别是区域性层状对流以及多层对流环可能在地幔中存在的现象 .
We assume that the heterogeneity in the Earth's mantle is caused by the thermal convection in it. First, we transform the seismic tomography data of the mantle into the density (or temperature) anomaly and take it as the driving force of the mantle convection. Then we take account of the three basic equations, which control the mantle convection system, to investigate the patterns of the mantle flow. We use the seismic tomograpy model SH12WM13 to calculate the mantle convection patterns with different Rayleigh numbers up to 10 6. Results show that the mantle convection patterns depend on not only the seismic tomography data, but also the Rayleigh numbers very much. When the Rayleigh number is higher, the convection pattern is more complex. Particularly, there is regional layer convection and multiple scales convection in the modeled mantle. If this result is to be approved, it will change greatly our knowledge about the structure of the mantle thermal dynamical processes.
We assume that the heterogeneity in the Earth's mantle is caused by the thermal convection in it. First, we transform the seismic tomography data of the mantle into the density (or temperature) anomaly and take it as the driving force of the mantle convection. Then we take account of the three basic equations, which control the mantle convection system, to investigate the patterns of the mantle flow. We use the seismic tomograpy model SH12WM13 to calculate the mantle convection patterns with different Rayleigh numbers up to 10 6. Results show that the mantle convection patterns depend on not only the seismic tomography data, but also the Rayleigh numbers very much. When the Rayleigh number is higher, the convection pattern is more complex. Particularly, there is regional layer convection and multiple scales convection in the modeled mantle. If this result is to be approved, it will change greatly our knowledge about the structure of the mantle thermal dynamical processes.
引文
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[2] SchubertG ,ZebibA .Thermalconvectionofaninternallyheatedin finitePrandtlnumberfluidinasphericalshell.Geophys.Astrophys.FluidDyn.,1980,15:65
[3] PeltierWR .Mantleconvectionandviscoelasticity.Ann.Rev.Flu idMech.,1985,17:561～608
[4] HagerBH ,MCurnis.MantleconvectionandthestateontheEarth’sinterior.Rev.Geophys.,1987,25:1277～1285
[5] FuRS .Anumericalstudyoftheeffectsofboundaryconditionsonmantleconvectionmodelsconstrainedtofitthelowdegreegeoidcoef ficients.Phys.Earth.Planet.Inter.,1986,44:257～263
[6] OlsonP ,GSchubertetal.Small scaleconvectionintheD″ layerandtheroughnessofthecore mantleboundary.Eos(Trans.AGU),1986,67:1201
[7] YamajiA .Periodichotspotdistributionandsmall scaleconvectionintheuppermantle,Earthandplanet.Sci.Lett.,1992,109:107～116
[8] BussFH .Multiplesolutionsforconvectioninatwocomponentfluid.Geophys.Res.Lett.,1982,9:519～522
[9] 叶正仁.地幔对流大地水准面异常和板块运动.现今地球动力学问题讨论会论文集.北京:地震出版社,1994.72～80YEZhengren.Mantleconvectiongeoidanomalyandplatemotions.In:ProblemsofPresentGeodynamics.Beijing:SeismologicalPress,1994.72～80
[10] YeZR ,ZhangXW ,TengCK .Mantleflowwithexistenceofplateandgenerationofthetoroidalfield.PAGEOPH ,1996,146(34):573～587
[11] KelloggHL ,BHHager,RVanderHilst.Compositionalstratifica tioninthedeepmantle.Science,1999,283:1881～1884
[12] McNuttM .Themantle’slavalamp.Nature,1999,402:739～740
[13] HagerBH ,ClaytonRW ,RichardsMA .Lowermantleheterogene ity,dynamictopographyandthegeoid.Nature,1985,313:541～545
[14] RichardY ,VignyC .Mantledynamicswithinducedplatetectonics.J.Geophys.Res.,1989,14:7543～7559
[15] HagerHB ,RWClayton.Constraintsonthestructureonmantleconvectionusingseismicobservations,flowmodelandthegeoid.In:WRPeltier,ed.Mantleconvection,PlateTectonicsandGlobalDy namics.NewYork:GordonandBreachSci.Publish.1989.657～763
[16] ForteAM ,ARPeltier.Viscousflowmodelsofglobalgeophysicalobservations1.Forwardproblems.J .Geophys.Res.,1991,96:20131～20159
[17] ForteAM ,RLWoodward,AMDzeiwonski.Jointinversionsofseismicandgeodynamicdataformodelsforthree dimensionalmantleheterogeneity.J .Geophys.Res.,1994,99:21857～21877
[18] ThoravalC ,PMachetle,ACasenave.Locallylayeredconvectionin ferredfromdynamicmodelsoftheEarth’smantle.Nature,1995,375:777～780
[19] ChandrasekharV .HydrodynamicandHydromagneticStability.Ox ford:ClarendonPress,1961.652
[20] HaxbyWF ,JKWeissel.Evidenceforsmall scalemantleconvectionfromSEASATaltimeterdata.J.Geophys.Res.,1986,91:3507～3520
[21]BaudryN ,LKroenke.Intermediate wavelength(400—600km)SouthPacificgeoidundulations:theirrelationshipofvolcanicchains.EarthPlanet.Sci.Lett.,1991,102:430～443
[22] CserepesLD ,AYuen,BASchroeder.Effectofthemid mantleviscosityandphase transitionstructureon3Dmantleconvection.Phys.EarthPlanet.Inter.,2000,118:135～148
[23] DubuffectF ,MRabinwwicz,M .Monnereau.Multiplescalesinman tleconvection.EarthPlanet.Sci.Lett.,2000,178:351～366
[24]FuRS ,HuangJH .Thermodynamicalresponseofthemantletoamovingupperboundary.Phys.EarthPlanet.Inter.,1992,71:112～125
[25] 傅容珊,黄建华.利用地球物理观测反演地幔对流模型.地球物理学报,1993,36(3):298～307FURongshan,HUANGJianhua.Inversionofmantleconvectionmod elusingseveralgeophysicaldata.ChineseJ .Geophys.(ActaGeo physicaSinica),1993,36(3):298～307
[26] 傅容珊,董树谦,黄建华等.地震层析成像-地幔对流新模型的研究.地球物理学报,2002,45(Suppl.):136～143FURongshan,DONGShuqian,HUANGJianhua,etal.Anewman tleconvectionmodelconstainedbyseismictomography.ChineseJ .Geophys.,2002,45(Suppl.):136～143
[27] SuWJ,WoodwardRL ,DzeiwonskiAM .Degree12modelofshearvelocityheterogeneityinthemantle.J .Geophys.Res.,1994,99:6945～6980
[28] MastersG ,JordanTH ,SilverPG ,etal.Asphericalearthstruc turefromfundamentalspherical modedata.Nature,1982,298:609～613
[29] DziewonskiAM ,AndersonDL .PreliminaryreferenceEarthmodel.Phys.EarthPlanetInter.,1981,25:297～356
[30] 傅容珊,陈 凌,黄建华等.全球地震层析地幔密度横向不均匀及大陆动力学.地球物理学进展,1995,10(3):51～62FURongshan,CHENLing,HUANGJianhua,e
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