云南地区地脉动噪声特征分析研究
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摘要
对地震台站记录到的长时间背景噪声进行互相关可以得到台站间的格林函数,进而可以对地下介质波速结构和波速变化进行研究。对背景噪声来源方向和时空演化规律的分析,是提高结果可靠性的重要基础。本文利用分布在云南境内的43个宽频带固定台站2008—2010年的垂直分量记录,计算了两两台站之间的互相关函数,并用平均能量流的方法研究了云南地区5～10s以及10～20s两个频段内地脉动噪声能量的空间分布和时间演化。研究结果表明,云南地区5～10s的地脉动噪声能量优势方向存在明显的季节性变化,夏季优势能量方位角为180°～210°,冬季则为70°～100°。而10～20s的地脉动噪声优势方向方位角较为稳定,为180°～210°。在这两个频段内噪声能量的强度都表现出了较强的季节性变化。同时发现在5～10s频段瑞利面波之前存在视速度接近30km/s的前驱信号,并对其可能来源进行了分析。
The Green′s function between two stations can be extracted by cross correlating long time range ambient noise recorded by these stations,thus can be used for subsurface velocity inversion as well as time lapse monitoring of velocity variation.The knowledge of the variation of ambient noise direction and strength is important to improve the precision of these researches.Using the vertical component records from the Yunnan regional broadband seismic stations from 2008 to 2010,we calculated the noise cross correlation functions between each stations,then used the normalized background energy flux measurement to study the characteristicss of ambient noise in Yunan region,especially for secondary microseism period in 5~10s and primary microseism in 10~20 s.A significant direction variation of 5~10 s noise energy is observed,whose azimuth is 180°~210° in the Summer and moves to 70°~100° in the Winter.The direction of 10~20 s ambient noise is more stable covering 180°~210°.The strength of ambient noise of both types shows seasonal variation.We also observed strong near-zero arrivals with apparent velocity about 30 km/s,the possible mechanics of this precursors are discussed.
The Green′s function between two stations can be extracted by cross correlating long time range ambient noise recorded by these stations,thus can be used for subsurface velocity inversion as well as time lapse monitoring of velocity variation.The knowledge of the variation of ambient noise direction and strength is important to improve the precision of these researches.Using the vertical component records from the Yunnan regional broadband seismic stations from 2008 to 2010,we calculated the noise cross correlation functions between each stations,then used the normalized background energy flux measurement to study the characteristicss of ambient noise in Yunan region,especially for secondary microseism period in 5~10s and primary microseism in 10~20 s.A significant direction variation of 5~10 s noise energy is observed,whose azimuth is 180°~210° in the Summer and moves to 70°~100° in the Winter.The direction of 10~20 s ambient noise is more stable covering 180°~210°.The strength of ambient noise of both types shows seasonal variation.We also observed strong near-zero arrivals with apparent velocity about 30 km/s,the possible mechanics of this precursors are discussed.
引文
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[25]Stutzmann E.,Schimmel M,Patau G,et al.Global climate imprint on seismic noise[J].GeochemGeophys Geosyst,2009,10:Q11004.
[26]郑秀芬,欧阳飚,张东宁,等.“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,2009,52(5):1 412-1 417.
[27]鲁来玉,何正勤,丁志峰,等.华北科学探测台阵背景噪声特征分析[J].地球物理学报,2009,52(10):2 566-2 572.
[28]Snieder R.Extracting the green's function from the correlation of coda waves:A derivation based onstationary phase[J].Phys Rev E,2004,69.
[29]Longuet-Higgins M S.A theory of the origin of microseisms[J].Philos Trans R.Soc London,SerA,1950,243:1-35.
[30]Kedar S,Longuet-Higgins M,Webb F,et al.The origin of deep ocean microseisms in the NorthAtlantic Ocean[J].Proc R Soc A,2007,464:777-793.
[31]Landès M,Hubans F,Shapiro N M,et al.Origin of deep ocean microseisms by using teleseismicbody waves[J].J Geophys Res,2010,115:B05302.
[32]Koper K D,de Foy B.Seasonal anisotropy in short period seismic noise recorded in south Asia[J].Bull Seismol Soc Am,2008,98:3 033-3 045.
[33]Chen Y N,Gung Y,You S H,et al.Characteristics of short period secondary microseisms(SPSM)in Taiwan:The influence of shallow ocean strait on SPSM[J].Geophys Res Lett,2011,38:L04305.
[34]Shapiro N M,Ritzwoller M H,Bensen G D.Source location of the 26sec microseism from crosscorrelations of ambient seismic noise[J].Geophys Res Lett,2006,33:L18310.
[35]Zeng X,Ni S.A persistent localized microseismic source near the Kyushu Island,Japan[J].Geo-phys Res Lett,2010,37:L24307.
[36]Koper K D,Seats K,Benz H.On the composition of Earth′s short-period seismic noise field[J].Bull Seismol Soc Am,2010,100:606-617.
[37]Zhang J,Gerstoft P,Bromirski P D.Pelagic and coastal sources of P wave microseisms:Generationunder tropical cyclones[J].Geophys Res Lett,2010,37:L15301.
[2]Wapenaar K.Retrieving the elasto dynamic Green′s function of an arbitrary inhomogeneous mediumby cross correlation[J].Phys Rev Lett,2004,93:254-301.
[3]Shapiro N M,Campillo M.Emergence of broadband Rayleigh waves from correlations of the ambi-ent seismic noise[J].Geophys Res Lett,2004,31:L07614.
[4]Bensen G D,Ritzwoller M H,Barmin M P,et al.Processing seismic ambient noise data to obtainreliable broad-band surfacewave dispersion measurements[J].Geophys J Int,2007,169:1 239-1 260.
[5]Shapiro N M,Campillo M,Stehly L,et al.High resolution surface wave tomography from ambientseismic noise[J].Science,2005,307:1 615-1 618.
[6]Sabra K G,Gerstoft P,Roux P,et al.Surfacewave tomography from microseism in southern Cali-fornia[J].Geophys Res Lett,2005,32:L14311.
[7]Fang L,Wu J,Ding Z,et al.High resolution Rayleigh wave group velocity tomography in NorthChina from ambient seismic noise[J].Geophys J Int,2010,181:1 171-1 182.
[8]Zheng S,Sun X,Song X,et al.Surface wave tomography of China from ambient seismic noise cor-relation[J].Geochem Geophys Geosyst,2008,9:Q05020.
[9]Zheng X,Jiao W,Zhang C,et al.Short-period Rayleigh wave group velocity tomography throughambient noise cross-correlation in Xinjiang,northwest China[J].Bull Seismol Soc Am,2010,100:1 350-1 355.
[10]李昱,姚华建,刘启元,等.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,2010,53(4):842-852.
[11]Yang Y,Ritzwoller M H,Levshin A,et al.Ambient noise Rayleigh wave tomography across Eu-rope[J].Geophys J Int,2007,168:259-274.
[12]Bensen G D,Ritzwoller M H,Shapiro N M.Broadband ambient noise surface wave tomographyacross the United States[J].J Geophys Res,2008,113:B05306.
[13]Lin F C,Moschetti M P,Ritzwoller M H.Surface wave tomography of the western United Statesfrom ambient seismic noise:Rayleigh and Love wave phase velocity maps[J].Geophys J Int,2008,173:281-298.
[14]Yao H,Beghein C,Van der Hilst R D.Surface-wave array tomography in SE Tibet from ambientseismic noise and two-station analysis:Ⅱ-Crustal and upper mantle structure[J].Geophys J Int,2008,173:205-219.
[15]Nishida K,Montagner J,Kawakatsu H.Global surface wave tomography using seismic hum[J].Science,2009,326:112-112.
[16]Brenguier F,Shapiro N M,Campillo M,et al.Towards forecasting volcanic eruptions using seismicnoise[J].Nat Geosci,2008,1:126-130.
[17]Brenguier F,Campillo M,Hadziioannou C,et al.Postseismic relaxation along the San AndreasFault at Parkfield from continuous seismological observations[J].Science,2008,321:1 478-1 481.
[18]刘志坤,黄金莉.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,2010,53(4):853-863.
[19]Cheng X,Niu F,Wang B.Coseismic velocity change in the rupture zone of the 2008 MW7.9Wen-chuan earthquake observed from ambient seismic noise[J].Bull Seismol Soc Am,2010,100(5B):2 539-2 550.
[20]Peterson J.Observation and Modelling of background Seismic Noise[M].USGS Open File Report,1993.93-322.
[21]Hasselmann K A.A stratistical analysis of the generation of microseisms[J].Rev Geophys,1963,1:177-209.
[22]Cessaro R K.Source of primary and secondary microseisms[J].Bull Seismol Soc Am,1994,84:142-156.
[23]Stehly L,Campillo M,Shapiro N M.A study of the seismic noise from its long-range correlationproperties[J].J Geophys Res,2006,111:B10306.
[24]Yang Y,Ritzwoller M H.Characteristics of ambient seismic noise as a source for surface wavetomography[J].Geochem Geosphys Geosyst,2008,9:Q02008.
[25]Stutzmann E.,Schimmel M,Patau G,et al.Global climate imprint on seismic noise[J].GeochemGeophys Geosyst,2009,10:Q11004.
[26]郑秀芬,欧阳飚,张东宁,等.“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,2009,52(5):1 412-1 417.
[27]鲁来玉,何正勤,丁志峰,等.华北科学探测台阵背景噪声特征分析[J].地球物理学报,2009,52(10):2 566-2 572.
[28]Snieder R.Extracting the green's function from the correlation of coda waves:A derivation based onstationary phase[J].Phys Rev E,2004,69.
[29]Longuet-Higgins M S.A theory of the origin of microseisms[J].Philos Trans R.Soc London,SerA,1950,243:1-35.
[30]Kedar S,Longuet-Higgins M,Webb F,et al.The origin of deep ocean microseisms in the NorthAtlantic Ocean[J].Proc R Soc A,2007,464:777-793.
[31]Landès M,Hubans F,Shapiro N M,et al.Origin of deep ocean microseisms by using teleseismicbody waves[J].J Geophys Res,2010,115:B05302.
[32]Koper K D,de Foy B.Seasonal anisotropy in short period seismic noise recorded in south Asia[J].Bull Seismol Soc Am,2008,98:3 033-3 045.
[33]Chen Y N,Gung Y,You S H,et al.Characteristics of short period secondary microseisms(SPSM)in Taiwan:The influence of shallow ocean strait on SPSM[J].Geophys Res Lett,2011,38:L04305.
[34]Shapiro N M,Ritzwoller M H,Bensen G D.Source location of the 26sec microseism from crosscorrelations of ambient seismic noise[J].Geophys Res Lett,2006,33:L18310.
[35]Zeng X,Ni S.A persistent localized microseismic source near the Kyushu Island,Japan[J].Geo-phys Res Lett,2010,37:L24307.
[36]Koper K D,Seats K,Benz H.On the composition of Earth′s short-period seismic noise field[J].Bull Seismol Soc Am,2010,100:606-617.
[37]Zhang J,Gerstoft P,Bromirski P D.Pelagic and coastal sources of P wave microseisms:Generationunder tropical cyclones[J].Geophys Res Lett,2010,37:L15301.
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