核幔边界的速度结构对PKPab波形的影响
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摘要
用地球的自由振荡研究地球内部结构、速度间断面、密度分布等具有射线理论不可替代的优点。而地球的自由振荡可以用简正振型来表示,用简正振型叠加方法合成的PKP波理论地震图,其PKPab波震相和PKPdf波震相的走时与射线理论计算的理论走时基本一致,并且研究了在地幔底部至核幔边界上方300 km处,压缩波的速度梯度的变化对PKPab波振幅的影响,从而证明当波以接近掠射角或者大于掠射角入射时,会有漏能现象的发生,或者可称之为隧道效应。发现用3个不同模型合成的地震图,在震中距相同的情况下,核幔边界上P波速度梯度大的,其PKPab波的振幅较小一些。这也进一步说明核幔边界上方P波速度梯度的变化对漏能现象有一定程度的影响。
The earth free oscillation can be used to constrain structure of the earth interior,including velocity,discontinuity as well as density distribution.Surface wave and body wave can also be implemented by normal modes summation. Synthetics seismograms via normal modes summation agree well in travel times with those from ray theoretical algorithm.We investigate the effects on PKPab amplitudes for three earth models with different P velocity up to 300km above Coremantle boundary.These results suggest that energy can leak into outer core even when P waves turns above core mantle boundary,which is just the case of tunneling effect.
The earth free oscillation can be used to constrain structure of the earth interior,including velocity,discontinuity as well as density distribution.Surface wave and body wave can also be implemented by normal modes summation. Synthetics seismograms via normal modes summation agree well in travel times with those from ray theoretical algorithm.We investigate the effects on PKPab amplitudes for three earth models with different P velocity up to 300km above Coremantle boundary.These results suggest that energy can leak into outer core even when P waves turns above core mantle boundary,which is just the case of tunneling effect.
引文
[1]Anderson.D.L and Given.J.W.Absorption band Q model for the Earth[J].J.Geophys.Res.87.3 898-3 904.
[2]Anderson and Given.,Absportion-band Q model for the earth[J].JGR 87.,1982,3 893-3 904.
[3]Thorne Lay and Terry C.W.,Modern Global Seismology[J].Chapter 7 Determination of earth structure,1995,301-302.
[4]Sheng-Nian Luo,Sidao Ni,and Donald V.Helmberger Evidence for a sharp lateral variation of velocity at the core^mantle boundary from multi-pathed PKPab[J].Earth and Planetary Science Letters 189.,2001,155-164.
[5]Richards,P.G.,On the adequacy of plane-wave reflection/transmission coefficients in the analysis of seismic body waves[J].Bulletin of theSeismological society of America.,66,3,.1976,701-717.
[6]S.Houard,J.L.Plantet,J.P.Massotand,H.C.Nataf.Amplitudes of core waves near the pkp caustic,from nuclear explosions in the south pacif-ic recorded at the“laboratoirede detectionet geophysique”network,in france[J].Bulletin of the Seismological Society of America,1993,83,6,1835-1 854.
[7]Gilbert,F.,Excitation of normal modes of the Earth by earthquake source[J].Geophys.J.R.astr.Soc.,1971,22,223-226.
[8]R.Widmer-Schnidrig.,Free oscillations illuminate the mantle[J].,Natur.,1999.
[9]Resovsky,J.S.&Ritzwoller,M.H.New and refined constraints on three-dimensional Earth structure from normal modes below 3 mHz[J].Journal of Geophysical Research,Volume 103,Issue B1,1998,783-810.
[10]Philippe Lognonne,¨1,2 Eric Cle¨ve¨de¨2 and Hiroo Kanamori3.,Computation of seismograms and atmospheric oscillations by normal-modesummation for a spherical earth model with realistic atmosphere[J].,Geophys.J.Int.1998,135,388-406.
[11]A Deuss,JH Woodhouse,et al.The observation of inner core shear waves[J].Geophys.J.Int.,Volume 142 Issue 1 2000,67-73.
[12]Caroline Beghein,Joseph S.Resovsky and Jeannot Trampert.,P and S tomography using normal-mode and surface waves data with a neigh-bourhood algorithm[J].Geophys.J.Int.149,2002,646-658.
[13]Aki and Richards,P.G Quantitative Seismology[M].1980.
[14]Dahlen,F.A.,Tromp,J Theoretical Global Seismology[J],Princeton University Press,New Jersey 1998.
[15]Dziewonski Adom L,Anderson don L.,Preliminary reference earth model[J].,Physics of the Earth and Planetary Interiors,Volume 1981,25,Issue 4,297-356.
[2]Anderson and Given.,Absportion-band Q model for the earth[J].JGR 87.,1982,3 893-3 904.
[3]Thorne Lay and Terry C.W.,Modern Global Seismology[J].Chapter 7 Determination of earth structure,1995,301-302.
[4]Sheng-Nian Luo,Sidao Ni,and Donald V.Helmberger Evidence for a sharp lateral variation of velocity at the core^mantle boundary from multi-pathed PKPab[J].Earth and Planetary Science Letters 189.,2001,155-164.
[5]Richards,P.G.,On the adequacy of plane-wave reflection/transmission coefficients in the analysis of seismic body waves[J].Bulletin of theSeismological society of America.,66,3,.1976,701-717.
[6]S.Houard,J.L.Plantet,J.P.Massotand,H.C.Nataf.Amplitudes of core waves near the pkp caustic,from nuclear explosions in the south pacif-ic recorded at the“laboratoirede detectionet geophysique”network,in france[J].Bulletin of the Seismological Society of America,1993,83,6,1835-1 854.
[7]Gilbert,F.,Excitation of normal modes of the Earth by earthquake source[J].Geophys.J.R.astr.Soc.,1971,22,223-226.
[8]R.Widmer-Schnidrig.,Free oscillations illuminate the mantle[J].,Natur.,1999.
[9]Resovsky,J.S.&Ritzwoller,M.H.New and refined constraints on three-dimensional Earth structure from normal modes below 3 mHz[J].Journal of Geophysical Research,Volume 103,Issue B1,1998,783-810.
[10]Philippe Lognonne,¨1,2 Eric Cle¨ve¨de¨2 and Hiroo Kanamori3.,Computation of seismograms and atmospheric oscillations by normal-modesummation for a spherical earth model with realistic atmosphere[J].,Geophys.J.Int.1998,135,388-406.
[11]A Deuss,JH Woodhouse,et al.The observation of inner core shear waves[J].Geophys.J.Int.,Volume 142 Issue 1 2000,67-73.
[12]Caroline Beghein,Joseph S.Resovsky and Jeannot Trampert.,P and S tomography using normal-mode and surface waves data with a neigh-bourhood algorithm[J].Geophys.J.Int.149,2002,646-658.
[13]Aki and Richards,P.G Quantitative Seismology[M].1980.
[14]Dahlen,F.A.,Tromp,J Theoretical Global Seismology[J],Princeton University Press,New Jersey 1998.
[15]Dziewonski Adom L,Anderson don L.,Preliminary reference earth model[J].,Physics of the Earth and Planetary Interiors,Volume 1981,25,Issue 4,297-356.
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