SS波形复杂性研究
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摘要
通过使用传播矩阵方法计算全波场理论地震图和对观测资料分析,对40°—180°震中距范围内SS波形复杂性的影响因素进行了定量探讨.研究表明,S波在反射点的莫霍面和地表产生的透射转换与反射转换震相,是造成SS波形复杂化的主要因素;反射点莫霍界面两侧的波速差异程度对各转换震相幅度有重要影响.当反射点地壳比较薄时,台站地壳也对SS波形的复杂化起作用.这些影响因素共同造成了SS的切向与径向分量之间的分裂时间与反射点地壳厚度具有明显正相关性.对SS反射点分别落在中国东部和西部的两组观测波形资料进行了分析,并测量了切向与径向之间的分裂时间.结果表明,地壳较厚的西部的分裂时间明显大于地壳较薄的东部的分裂时间,并有可能发展一种利用SS分裂时间来估算地壳厚度的新方法.
Some influential factors on the complication of SS waveform (with epicentral distance within 40°--180°) are analyzed quantitatively by calculating the full-wave synthetic seismogram using propagation matrix method. Our results show that the transmission-conversion and reflection-conversion phases of S wave at the interface of Moho and free surface beneath bounce points are mainly responsible for the complication of SS waveform, the velocity contrast between the two sides of Moho boundary under SS bounce point also has great effects on the amplitudes of all the conversion and the reverberation phases; the properties of the crust at seismic station also play a role in the complication of SS waveform while the crustal thickness beneath bounce point is thinner relatively. At the same time, two sets of real SS waveform data at the two positions in eastern and western China are analyzed, and the splitting time between SS transverse component and radial component is measured by cross-correlation. Our analysis demonstrates that there is a positive correlation between crustal thickness and the splitting time because of the influences of adjacent conversion and reverberation phases, the splitting time in west with thick crust is obviously greater than that in the east with thin crust. Moreover, it is promising that one new method of measurement of crustal thickness will be developed by using the observed SS splitting time.
Some influential factors on the complication of SS waveform (with epicentral distance within 40°--180°) are analyzed quantitatively by calculating the full-wave synthetic seismogram using propagation matrix method. Our results show that the transmission-conversion and reflection-conversion phases of S wave at the interface of Moho and free surface beneath bounce points are mainly responsible for the complication of SS waveform, the velocity contrast between the two sides of Moho boundary under SS bounce point also has great effects on the amplitudes of all the conversion and the reverberation phases; the properties of the crust at seismic station also play a role in the complication of SS waveform while the crustal thickness beneath bounce point is thinner relatively. At the same time, two sets of real SS waveform data at the two positions in eastern and western China are analyzed, and the splitting time between SS transverse component and radial component is measured by cross-correlation. Our analysis demonstrates that there is a positive correlation between crustal thickness and the splitting time because of the influences of adjacent conversion and reverberation phases, the splitting time in west with thick crust is obviously greater than that in the east with thin crust. Moreover, it is promising that one new method of measurement of crustal thickness will be developed by using the observed SS splitting time.
引文
Astiz L,Earle P S,Shearer P M.1996.Global stacking of broadband seismograms[J].Seismo Res Lett,67[4]:8--18.
Bhattacharyya J,Masters G,Shearer P.1996.Global lateral variations of shear wave attenuation in the upper mantle[J].J Geophys Res,101[B10]:22273--22289.
Grand S P.2002.Mantle shear-wave tomography and the fate of subducted slabs[J].Phil Trans R Soc Lond A,360:2475--2491.
Kennett B L N,Engdahl E R.1991.Travelti mes for global earthquake location and phase identification[J].Geophys JInt,105:429--465.
Lawrence J F,Shearer P M.2006.A global study of transition zone thickness using receiver functions[J].J GeophysRes,111[B06307],doi:10.1029/2005JB003973.
Ma Y,Wang R,Zhou H.2008.An i mprovement to the orthonormalization method for efficient computation of plane-wave response in multi-layered media[J].Journal ofthe Graduate School of the Chinese Academy of Sciences,25[1]:47--53.
Reid F J L,Woodhouse J H,Heijst HJ.2001.Upper mantle attenuation and velocity structure from measurements ofdifferential S phases[J].Geophys J Int,145:615--630.
Schmerr N,Garnero E.2006.Investigation of upper mantle discontinuity structure beneath the central Pacific using SSprecursors[J].J Geophys Res,11[B08305],doi:10.1029/2005JB004197.
Wang R.1999.Asi mple orthonormalization method for stable and efficient computation of Green′s functions[J].BullSeism Soc Amer,89:733--741.
Wolfe CJ,Silver P G.1998.Seismic anisotropy of oceanic upper mantle:Shear wave splitting methodologies and oberva-tions[J].J Geophys Res,103[B1]:749--771.
Yang X,Fischer K M.1994.Constrainsts on north Atlantic upper mantle anisotropy fromS and SS phases[J].GeophysRes Lett,21[4]:309--312.
Bhattacharyya J,Masters G,Shearer P.1996.Global lateral variations of shear wave attenuation in the upper mantle[J].J Geophys Res,101[B10]:22273--22289.
Grand S P.2002.Mantle shear-wave tomography and the fate of subducted slabs[J].Phil Trans R Soc Lond A,360:2475--2491.
Kennett B L N,Engdahl E R.1991.Travelti mes for global earthquake location and phase identification[J].Geophys JInt,105:429--465.
Lawrence J F,Shearer P M.2006.A global study of transition zone thickness using receiver functions[J].J GeophysRes,111[B06307],doi:10.1029/2005JB003973.
Ma Y,Wang R,Zhou H.2008.An i mprovement to the orthonormalization method for efficient computation of plane-wave response in multi-layered media[J].Journal ofthe Graduate School of the Chinese Academy of Sciences,25[1]:47--53.
Reid F J L,Woodhouse J H,Heijst HJ.2001.Upper mantle attenuation and velocity structure from measurements ofdifferential S phases[J].Geophys J Int,145:615--630.
Schmerr N,Garnero E.2006.Investigation of upper mantle discontinuity structure beneath the central Pacific using SSprecursors[J].J Geophys Res,11[B08305],doi:10.1029/2005JB004197.
Wang R.1999.Asi mple orthonormalization method for stable and efficient computation of Green′s functions[J].BullSeism Soc Amer,89:733--741.
Wolfe CJ,Silver P G.1998.Seismic anisotropy of oceanic upper mantle:Shear wave splitting methodologies and oberva-tions[J].J Geophys Res,103[B1]:749--771.
Yang X,Fischer K M.1994.Constrainsts on north Atlantic upper mantle anisotropy fromS and SS phases[J].GeophysRes Lett,21[4]:309--312.
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