云南地区背景噪声互相关函数中体波信号来源初探
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摘要
利用云南地区43个宽频带地震台站记录的2008～2010年垂直分量数据,计算了台站对间的互相关函数并得到了5～40 s周期的瑞利面波信号。研究发现在5～10 s周期范围内,瑞利面波信号之前存在很强的前驱信号,该信号能量优势频段为0.1～0.2 Hz,其到时接近噪声互相关函数零点,视速度约为30 km/s。该信号到时随季节存在正负交替变化,进一步的质点分析表明该信号为出射角较小的P波信号。参考已有的研究,认为远场地脉动噪声源中的P波信号穿过地球深部到达云南地区,形成了噪声互相关函数中视速度较高的体波信号,并且相关的噪声源位置在冬季和夏季分别位于北太平洋和南印度洋,具有明显的季节性空间变化。
Using vertical component records observed at 43 broad-band seismic stations from 2008 to 2010 in Yunnan,we calculate the noise-cross correlation functions between each station-pair and obtain Raleigh surface wave in the period from 5s to 40s.We find that in the period from 5s to 10s,and before Rayleigh wave,there is a strong precursory wave whose dominant frequency band is between 0.1 Hz and 0.2 Hz and whose arrival time is near the zero of cross correlation functions.Moreover its negative arrival-time in Winter alternates with the positive ones in Summer.Through further analysis of particle-motion,we confirm that this wave is P-wave with smaller reflection angle whose apparent velocity is about 30km/s.Referring to the relevant research results,we conclude that originating from the ambient micro-tremor noise source at a teleseismic distance,P-wave travels through deep earth to Yunnan and reaches a higher apparent velocity.The ambient noise source,which locates in South Indian Ocean in Summer and North Pacific Ocean in Winter,varies seasonally and spatially.
Using vertical component records observed at 43 broad-band seismic stations from 2008 to 2010 in Yunnan,we calculate the noise-cross correlation functions between each station-pair and obtain Raleigh surface wave in the period from 5s to 40s.We find that in the period from 5s to 10s,and before Rayleigh wave,there is a strong precursory wave whose dominant frequency band is between 0.1 Hz and 0.2 Hz and whose arrival time is near the zero of cross correlation functions.Moreover its negative arrival-time in Winter alternates with the positive ones in Summer.Through further analysis of particle-motion,we confirm that this wave is P-wave with smaller reflection angle whose apparent velocity is about 30km/s.Referring to the relevant research results,we conclude that originating from the ambient micro-tremor noise source at a teleseismic distance,P-wave travels through deep earth to Yunnan and reaches a higher apparent velocity.The ambient noise source,which locates in South Indian Ocean in Summer and North Pacific Ocean in Winter,varies seasonally and spatially.
引文
房立华,吴建平,吕作勇.2009.华北地区基于噪声的瑞利面波群速度层析成像[J].地球物理学报,52(3):663-671.
李昱,姚华建,刘启元,等.2010.川西地区台阵环境噪声瑞利波相速度层析成像[J].地球物理学报,53(4):842-852.
刘志坤,黄金莉.2010.利用背景噪声互相关研究汶川地震震源区地震波波速变化[J].地球物理学报,53(4):853-863.
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Cheng X,Niu F,Wang B.2010.Coseismic velocity change in the rupturezone of the2008Mw7.9Wenchuan earthquake observed from ambi-ent seismic noise[J].BSSA,100(5B):2539-2550.
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Fang L H,Wu J P,Ding Z F,et al.2010.High resolution Rayleigh wavegroup velocity tomography in North China from ambient seismic noise[J].Geophys J Int,181(2):1171-1182.
Forghani F,Snieder R.2010.Underestimation of body waves and feasibili-ty of surface-wave reconstruction by seismic interferometry[J].TheLeading Edge,29(7):790-794.
Kedar S,Longuet-Higgins M,Webb F,et al.2008.The origin of deep o-cean microseisms in the North Atlantic Ocean[J].Proc R Soc A,464(2901):777-793.
Kennett B L N,Engdahl E R.1991.Traveltimes for global earthquake lo-cation and phase identification[J].Geophys J Int,105(2):429-465.
Koper K D,Foy D B.2008.Seasonal anisotropy in short period seismicnoise recorded in south Asia[J].BSSA,98(6):3033-3045.
Koper K D,Seats K,Benz H.2010.On the composition of Earth's short-period seismic noise field[J].BSSA,100(2):606-617.
Landès M,Hubans F,Shapiro N M,et al.2010.Origin of deep ocean mi-croseisms by using teleseismic body waves[J].JGR,115,B05302,doi:10.1029/2009JB006918.
Lobkis O I,Weaver R L.2001.On the emergence of the Green's functionin the correlations of a diffuse field[J].J Acoust Soc Am,110(6):3011-3017.
Longuet-Higgins M S.1950.A theory of the origin of microseisms[J].Philos Trans R Soc London(Ser A),243(857):1-35.
Roux P,Sabra K G,Gerstoft P,et al.2005.P-waves from cross-correlationof seismic noise[J].Geophys Res Lett,32,L19303,doi:10.1029/2005GL023803.
Shapiro N M,Campillo M,Stehly L,et al.2005.High resolution surfacewave tomography from ambient seismic noise[J].Science,307(5715):1615-1618.
Shapiro N M,Campillo M.2004.Emergence of broadband Rayleigh wavesfrom correlations of the ambient seismic noise[J].Geophys ResLett,31,L07614,doi:10.1029/2004GL019491.
Snieder R.2004.Extracting the green's function from the correlation of co-da waves:A derivation based on stationary phase[J].Phys Rev E,69(2):doi:10.11031RhysRevE.69.046610.
Stehly L,Campillo M,Shapiro N M.2006.A study of the seismic noisefrom its long-range correlation properties[J].JGR(B10):111,B10306.
Wang W,Ni S,Wang B.2010.Composition of high frequency ambientnoise from cross-correlation:A case study using a small aperture ar-ray[J].Earthquake Science,23(5):433-438.
Wapenaar K.2004.Retrieving the elastodynamic Green's function of anarbitrary inhomogeneous medium by cross correlation[J].PhysicalReview Letters,93(25):doi:10.1103/Phys Rev Lett.93.254301.
Yang Y,Ritzwoller M H,Levshin A L,et al.2007.Ambient noise Ray-leigh wave tomography across Europe[J].Geophys J Int,168(3):259-274.
Yang Y,Ritzwoller M H.2008.Characteristics of ambient seismic noise asa source for surface wave tomography[J].Geochem Geosphy Geo-sys,9(2),doi:10.1029/2007GC001814.
Zhan Z,Ni S,Helmberger D V,et al.2010.Retrieval of Moho-reflectedshear wave arrivals from ambient seismic noise[J].Geophys J Int,182(1):408-420.
Zhang J P,Gerstoft P,Bromirski P D.2010.Pelagic and coastal sources ofP wave microseisms:Generation under tropical cyclones[J].Geo-phys Res Lett,37,L15301,doi:10.1029/2010GL044288.
Zhang J,Gerstoft P,Shearer P M,et al.2009.High-frequency P-wave seis-mic noise driven by ocean winds[J].Geophys Res Lett,36(9)doi:L09302,10.1029/2009GL037761.
Zheng S,Sun X,Song X,et al.2008.Surface wave tomography of Chinafrom ambient seismic noise correlation[J].Geochem Geophys Geo-syst,9(5):Q05020.
Zheng X,Jiao W,Zhang C,et al.2010.Short-period Rayleigh wave groupvelocity tomography through ambient noise cross-correlation in Xin-jiang,northwest China[J].BSSA,100(3):1350-1355.
李昱,姚华建,刘启元,等.2010.川西地区台阵环境噪声瑞利波相速度层析成像[J].地球物理学报,53(4):842-852.
刘志坤,黄金莉.2010.利用背景噪声互相关研究汶川地震震源区地震波波速变化[J].地球物理学报,53(4):853-863.
郑秀芬,欧阳飚,张东宁,等.2009.“国家数字测震台网数据备份中心”技术系统建设及其对汶川大地震研究的数据支撑[J].地球物理学报,52(5):1412-1417.
Brenguier F,Campillo M,Hadziioannou C,et al.2008a.Postseismic relax-ation along the San Andreas Fault at Parkfield from continuous seis-mological observations[J].Science,321(5895):1478-1481.
Brenguier F,Shapiro N M,Campillo M,et al.2008b.Towards forecastingvolcanic eruptions using seismic noise[J].Nature Geoscience,1(2):126-130.
Cheng X,Niu F,Wang B.2010.Coseismic velocity change in the rupturezone of the2008Mw7.9Wenchuan earthquake observed from ambi-ent seismic noise[J].BSSA,100(5B):2539-2550.
Crotwell H P,Owens T J,Ritsema J.1999.The taup toolkit:Flexible seis-mic travel-time and raypath utilities[J].Seismological Research Let-ters,70(2):154-160.
Draganov D,Wapenaar K,Mulder W,et al.2007.Retrieval of reflectionsfrom seismic background-noise measurements[J].Geophys ResLett,34(4),L04305,doi:10.1029/2006GL028735.
Fang L H,Wu J P,Ding Z F,et al.2010.High resolution Rayleigh wavegroup velocity tomography in North China from ambient seismic noise[J].Geophys J Int,181(2):1171-1182.
Forghani F,Snieder R.2010.Underestimation of body waves and feasibili-ty of surface-wave reconstruction by seismic interferometry[J].TheLeading Edge,29(7):790-794.
Kedar S,Longuet-Higgins M,Webb F,et al.2008.The origin of deep o-cean microseisms in the North Atlantic Ocean[J].Proc R Soc A,464(2901):777-793.
Kennett B L N,Engdahl E R.1991.Traveltimes for global earthquake lo-cation and phase identification[J].Geophys J Int,105(2):429-465.
Koper K D,Foy D B.2008.Seasonal anisotropy in short period seismicnoise recorded in south Asia[J].BSSA,98(6):3033-3045.
Koper K D,Seats K,Benz H.2010.On the composition of Earth's short-period seismic noise field[J].BSSA,100(2):606-617.
Landès M,Hubans F,Shapiro N M,et al.2010.Origin of deep ocean mi-croseisms by using teleseismic body waves[J].JGR,115,B05302,doi:10.1029/2009JB006918.
Lobkis O I,Weaver R L.2001.On the emergence of the Green's functionin the correlations of a diffuse field[J].J Acoust Soc Am,110(6):3011-3017.
Longuet-Higgins M S.1950.A theory of the origin of microseisms[J].Philos Trans R Soc London(Ser A),243(857):1-35.
Roux P,Sabra K G,Gerstoft P,et al.2005.P-waves from cross-correlationof seismic noise[J].Geophys Res Lett,32,L19303,doi:10.1029/2005GL023803.
Shapiro N M,Campillo M,Stehly L,et al.2005.High resolution surfacewave tomography from ambient seismic noise[J].Science,307(5715):1615-1618.
Shapiro N M,Campillo M.2004.Emergence of broadband Rayleigh wavesfrom correlations of the ambient seismic noise[J].Geophys ResLett,31,L07614,doi:10.1029/2004GL019491.
Snieder R.2004.Extracting the green's function from the correlation of co-da waves:A derivation based on stationary phase[J].Phys Rev E,69(2):doi:10.11031RhysRevE.69.046610.
Stehly L,Campillo M,Shapiro N M.2006.A study of the seismic noisefrom its long-range correlation properties[J].JGR(B10):111,B10306.
Wang W,Ni S,Wang B.2010.Composition of high frequency ambientnoise from cross-correlation:A case study using a small aperture ar-ray[J].Earthquake Science,23(5):433-438.
Wapenaar K.2004.Retrieving the elastodynamic Green's function of anarbitrary inhomogeneous medium by cross correlation[J].PhysicalReview Letters,93(25):doi:10.1103/Phys Rev Lett.93.254301.
Yang Y,Ritzwoller M H,Levshin A L,et al.2007.Ambient noise Ray-leigh wave tomography across Europe[J].Geophys J Int,168(3):259-274.
Yang Y,Ritzwoller M H.2008.Characteristics of ambient seismic noise asa source for surface wave tomography[J].Geochem Geosphy Geo-sys,9(2),doi:10.1029/2007GC001814.
Zhan Z,Ni S,Helmberger D V,et al.2010.Retrieval of Moho-reflectedshear wave arrivals from ambient seismic noise[J].Geophys J Int,182(1):408-420.
Zhang J P,Gerstoft P,Bromirski P D.2010.Pelagic and coastal sources ofP wave microseisms:Generation under tropical cyclones[J].Geo-phys Res Lett,37,L15301,doi:10.1029/2010GL044288.
Zhang J,Gerstoft P,Shearer P M,et al.2009.High-frequency P-wave seis-mic noise driven by ocean winds[J].Geophys Res Lett,36(9)doi:L09302,10.1029/2009GL037761.
Zheng S,Sun X,Song X,et al.2008.Surface wave tomography of Chinafrom ambient seismic noise correlation[J].Geochem Geophys Geo-syst,9(5):Q05020.
Zheng X,Jiao W,Zhang C,et al.2010.Short-period Rayleigh wave groupvelocity tomography through ambient noise cross-correlation in Xin-jiang,northwest China[J].BSSA,100(3):1350-1355.
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