利用接收函数计算地壳各向异性的可靠性分析及倾斜界面的影响
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摘要
使用接收函数研究壳幔速度间断面和速度结构已是常用的技术,但介质各向异性或倾斜的莫霍(Moho)界面,都会造成接收函数波形的复杂性。本文利用远震P波接收函数计算台站下方的地壳各向异性,通过信噪比测试和谐波分析两种方法来验证各向异性结果的可靠性。通过甘肃地震台网的两个台站记录,讨论各向异性和倾斜界面对接收函数的影响,结果显示,台站BYT(白银)下方具有各向异性,而台站WYT(渭源)下方由于可能存在倾斜界面,得到的各向异性结果则有待进一步分析。为了更好地认识倾斜界面对各向异性计算结果的影响,采用合成理论地震图,计算接收函数,然后利用合成接收函数进行各向异性分析。结果表明,计算得到的快波方向不会受到倾斜界面的影响,但是时间延迟会受到影响。
It is a very common technique to use receiver function to study velocity discontinuity surface between crust and upper-mantle and velocity structure.However,both anisotropy and dipping Moho can generate complicated waveforms of receiver function.We use P receiver function to determine crustal anisotropy,and then applying the signal-tonoise test and harmonic analysis to verify the reliability of the results.Using two stations from Gansu province,we discuss the influence of anisotropy and dipping interface to the receiver function.It shows that the crust beneath BYT is anisotropic,while because of dipping Moho,the crustal anisotropy beneath WYT remains to be determined.In order to better understand the effect of dipping Moho to anisotropy,we use program to generate synthetic seismogram and compute the receiver function,and then make anisotropy analysis from receiver function obtained.Results show that dipping Moho will not influence the fast direction of anisotropy,but the delay time between fast and slow waves.
It is a very common technique to use receiver function to study velocity discontinuity surface between crust and upper-mantle and velocity structure.However,both anisotropy and dipping Moho can generate complicated waveforms of receiver function.We use P receiver function to determine crustal anisotropy,and then applying the signal-tonoise test and harmonic analysis to verify the reliability of the results.Using two stations from Gansu province,we discuss the influence of anisotropy and dipping interface to the receiver function.It shows that the crust beneath BYT is anisotropic,while because of dipping Moho,the crustal anisotropy beneath WYT remains to be determined.In order to better understand the effect of dipping Moho to anisotropy,we use program to generate synthetic seismogram and compute the receiver function,and then make anisotropy analysis from receiver function obtained.Results show that dipping Moho will not influence the fast direction of anisotropy,but the delay time between fast and slow waves.
引文
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[18]Levin V,Roecker S,Graham P,et al.Seismic anisotropy indicators in Western Tibet:Shear wave splitting and receiver function analysis[J].Tectonophysics,2008,462:99-108.
[19]房立华,吴建平.倾斜界面和各向异性介质对接收函数的影响[J].地球物理学进展,2009,24:42-50.
[20]Liu H,Niu F.Estimating crustal seismic anisotropy with a joint analysis of radial and transverse receiver function data[J].Geophysical Journal International,2012,188(1):144-164.
[21]Vinnik L P.Detection of waves converted from P to SV in the mantle[J].Physics of the Earth and planetary interiors,1977,15(1):39-45.
[22]Ammon C J.The isolation of receiver effects from teleseismic P waveforms[J].Bulletin of the Seismological Society of America,1991,81(6):2504-2510.
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[24]Levin V,Park J.P-SH conversions in a flat-layered medium with anisotropy of arbitrary orientation[J].Geophysical Journal International,1997,131(2):253-266.
[25]Peng X,Humphreys E D.Moho dip and crustal anisotropy in northwestern Nevada from teleseismic receiver functions[J].Bulletin of the Seismological Society of America,1997,87(3):745-754.
[2]Wu Q,Li Y,Zhang R,et al.Wavelet modelling of broad-band receiver functions[J].Geophysical Journal International,2007,170(2):534-544.
[3]Ligorria J,Ammon C,Ligorria J,et al.Iterative deconvolution and receiver-function estimation[J].Bulletin of the Seismological Society of America,1999,89(5):1395-1400.
[4]Zheng T,Zhao L,Chen L.A detailed receiver function image of the sedimentary structure in the Bohai Bay Basin[J].Physics of the Earth and Planetary Interiors,2005,152(3):129-143.
[5]Savage M K.Lower crustal anisotropy or dipping boundaries?Effects on receiver functions and a case study in New Zealand[J].Journal of Geophysical Research:Solid Earth(1978-2012),1998,103(B7):15069-15087.
[6]Shibutani T,Sambridge M,Kennett B.Genetic algorithm inversion for receiver functions with application to crust and uppermost mantle structure beneath eastern Australia[J].Geophysical Research Letters,1996,23(14):1829-1832.
[7]Ammon C J,Zandt G.Receiver structure beneath the southern Mojave block,California[J].Bulletin of the Seismological Society of America,1993,83(3):737-755.
[8]Zhu L,Kanamori H.Moho depth variation in southern California from teleseismic receiver functions[J].Journal of Geophysical Research:Solid Earth(1978-2012),2000,105(B2):2969-2980.
[9]Zandt G,Ammon C J.Continental crust composition constrained by measurements of crustal Poisson′s ratio[J].Nature,1995,374(6518):152-154.
[10]Gao Y,Suetsugu D,Fukao Y,et al.Seismic discontinuities in the mantle transition zone and at the top of the lower mantle beneath eastern China and Korea:Influence of the stagnant Pacific slab[J].Physics of the Earth and Planetary Interiors,2010,183(1):288-295.
[11]Mcnamara D E,Owens T J.Azimuthal Shear Wave Velocity Anisotropy in the Basin and Range Province Using Moho Ps Converted Phases[J].Journal of Geophysical Research:Solid Earth(1978-2012),1993,98(B7):12003-12017.
[12]Levin V,Park J.Crustal anisotropy in the Ural Mountains Foredeep from teleseismic receiver functions[J].Geophysical Research Letters,1997,24(11):1283-1286.
[13]Vinnik L,Montagner J.Shear wave splitting in the mantle Ps phases[J].Geophysical Research Letters,1996,23(18):2449-2452.
[14]Girardin N,Farra V.Azimuthal anisotropy in the upper mantle from observations of P-to-S converted phases:application to southeast Australia[J].Geophysical Journal International,1998,133(3):615-629.
[15]Nagaya M,Oda H,Akazawa H,et al.Receiver Functions of Seismic Waves in Layered Anisotropic Media:Application to the Estimate of Seismic Anisotropy[J].Bulletin of the Seismological Society of America,2008,98(6):2990-3006.
[16]Mcnamara D E,Owens T J,Silver P G,et al.Shear wave anisotropy beneath the Tibetan Plateau[J].Journal of Geophysical Research,1994,99(B7):13613-13655.
[17]Frederiksen A W,Bostock M G.Modelling teleseismic waves in dipping anisotropic structures[J].Geophysical Journal International,2000,141(2):401-412.
[18]Levin V,Roecker S,Graham P,et al.Seismic anisotropy indicators in Western Tibet:Shear wave splitting and receiver function analysis[J].Tectonophysics,2008,462:99-108.
[19]房立华,吴建平.倾斜界面和各向异性介质对接收函数的影响[J].地球物理学进展,2009,24:42-50.
[20]Liu H,Niu F.Estimating crustal seismic anisotropy with a joint analysis of radial and transverse receiver function data[J].Geophysical Journal International,2012,188(1):144-164.
[21]Vinnik L P.Detection of waves converted from P to SV in the mantle[J].Physics of the Earth and planetary interiors,1977,15(1):39-45.
[22]Ammon C J.The isolation of receiver effects from teleseismic P waveforms[J].Bulletin of the Seismological Society of America,1991,81(6):2504-2510.
[23]Shiomi K,Park J.Structural features of the subducting slab beneath the Kii Peninsula,central Japan:Seismic evidence of slab segmentation,dehydration,and anisotropy[J].Journal of Geophysical Research:Solid Earth(1978-2012),2008,113(B10).
[24]Levin V,Park J.P-SH conversions in a flat-layered medium with anisotropy of arbitrary orientation[J].Geophysical Journal International,1997,131(2):253-266.
[25]Peng X,Humphreys E D.Moho dip and crustal anisotropy in northwestern Nevada from teleseismic receiver functions[J].Bulletin of the Seismological Society of America,1997,87(3):745-754.