利用地震层析成像研究地幔非对称结构
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摘要
利用 Su、Vasco、Hilst、Grand等提供的地震层析成像模型 ,根据实验室结果外推得到的地震波速度异常与密度异常之间的线性关系 ,将地幔进行分层、网格化处理 ,计算了地幔各层异常密度、密度异常质心和全地幔密度异常质心位置。结果表明 ,地幔密度异常表现出的总体特征是 :整体地幔密度异常为负值 ,上地幔异常大 ,中、下地幔密度异常较小 ;地幔整体和多数分层密度异常质心分布在北半球。这一结果反映 ,现今地幔热动力学演化呈现出南半球膨胀和北半球收缩的非对称基本格局。
On the basis of the relationship between seismic wave speed and density the non symmetric structures of the Earth mantle are investigated by using seismic tomography data set in this paper. We divide the Earth's mantle into several layers and every layer into grid blocks,then we calculate the anomaly mass center for every layer and for whole mantle as well. The results show that:(1)the density anomaly of whole mantle is negative;(2)the density anomalies are strong in the region of most upper mantle and near core-mantle boundary and week in the middle and lower mantles;(3)the density anomaly mass centers are distributed in the northern hemisphere for most layer and for whole mantle as well.These results infer us that the Earth's mantle manifests itself in a non symmetric structure in density distribution and it must be the consequence of the thermal dynamical mantale evolution, for example,the expansion of south hemisphere and constriction of north hemisphere of our planet.
On the basis of the relationship between seismic wave speed and density the non symmetric structures of the Earth mantle are investigated by using seismic tomography data set in this paper. We divide the Earth's mantle into several layers and every layer into grid blocks,then we calculate the anomaly mass center for every layer and for whole mantle as well. The results show that:(1)the density anomaly of whole mantle is negative;(2)the density anomalies are strong in the region of most upper mantle and near core-mantle boundary and week in the middle and lower mantles;(3)the density anomaly mass centers are distributed in the northern hemisphere for most layer and for whole mantle as well.These results infer us that the Earth's mantle manifests itself in a non symmetric structure in density distribution and it must be the consequence of the thermal dynamical mantale evolution, for example,the expansion of south hemisphere and constriction of north hemisphere of our planet.
引文
1 SuWeijia,RobertL Woodward andDziwonskiAdamM.Degree12 m odel of shear velocity heterogeneity in them antle[J].JournalGeophysicsResearch,1999,6945-6980.
2 VascoD W andL aneR Johnson.WholeEarth structureestimated from seismic arrival tim es[J].JournalGeo-physicsResearch,1998,2631,5671.
3 HilstRobD van der,SriWidiyantoro,KennethC,et al.Deep subduction and aspherical variations inP- wavespeed on the base of earth's m antle[C].See:TheCore-MantleBoundary region,1998,128.
4 FuRongshan,HuangJianhua andL iuWenzhong.Seismictomography:internal heterogeneity of mantle and its geo-dynam ical inferences[J].ActaGeophysicaSinica,1993,36(6):740-752.(inChinese)
5 AndreaMorelli andDziewonskiAdamM.Topography ofthe core- m antle boundary and lateral homogeneity of theliquid core[J].Nature,1987,325,678-683.
6 DziwonskiAdamM,AlessandroM Forte,SuWeijia,etal.Seismic tomography andGeodynamics[C].TheJeffreysVolumeGeophysicalMonograph76,IU GG Vol.16.
7 GrandS P,HilstR D Van der andWidiyantoroS.Globalseismic tomography:A snapshot of convection in the earth[J].J.Geophysics.Res.,1996,101,20053-20082.
8 WoodhouseJ H &DziewonskiA M.Mapping the upperm antle,Three- dim ensional modeling of earth structure byinversion of seism ic waveforms[J].J.GeophysRes.,1984,89,5953-5896.
9 SuW ,WoodwardR L andDziewonskiA M.Degree12m odel of shear velocity heterogeneity in the mantle[J].J.Geophys.Res.,1994,99,6945-6980.
10 Van derVoo,R SpakmanW andBijiwaardH .Tethyansubducted slab underIndia[J].EarthPlant.Sci.L ett.,1999,171,7-20.
11 Van derVooR.Mesozoic subducted slab underSiberia[J].Nature,1999b,21,246-249.
2 VascoD W andL aneR Johnson.WholeEarth structureestimated from seismic arrival tim es[J].JournalGeo-physicsResearch,1998,2631,5671.
3 HilstRobD van der,SriWidiyantoro,KennethC,et al.Deep subduction and aspherical variations inP- wavespeed on the base of earth's m antle[C].See:TheCore-MantleBoundary region,1998,128.
4 FuRongshan,HuangJianhua andL iuWenzhong.Seismictomography:internal heterogeneity of mantle and its geo-dynam ical inferences[J].ActaGeophysicaSinica,1993,36(6):740-752.(inChinese)
5 AndreaMorelli andDziewonskiAdamM.Topography ofthe core- m antle boundary and lateral homogeneity of theliquid core[J].Nature,1987,325,678-683.
6 DziwonskiAdamM,AlessandroM Forte,SuWeijia,etal.Seismic tomography andGeodynamics[C].TheJeffreysVolumeGeophysicalMonograph76,IU GG Vol.16.
7 GrandS P,HilstR D Van der andWidiyantoroS.Globalseismic tomography:A snapshot of convection in the earth[J].J.Geophysics.Res.,1996,101,20053-20082.
8 WoodhouseJ H &DziewonskiA M.Mapping the upperm antle,Three- dim ensional modeling of earth structure byinversion of seism ic waveforms[J].J.GeophysRes.,1984,89,5953-5896.
9 SuW ,WoodwardR L andDziewonskiA M.Degree12m odel of shear velocity heterogeneity in the mantle[J].J.Geophys.Res.,1994,99,6945-6980.
10 Van derVoo,R SpakmanW andBijiwaardH .Tethyansubducted slab underIndia[J].EarthPlant.Sci.L ett.,1999,171,7-20.
11 Van derVooR.Mesozoic subducted slab underSiberia[J].Nature,1999b,21,246-249.
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