中尺度涡影响下目的层地震成像的畸变与影响因素分析
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摘要
将PE方法与地震数值模拟方法相结合研究了中尺度涡影响下目标地层成像的畸变.模拟了不同声源频率、不同水深条件下的地震波场.计算结果发现,中尺度涡的存在使得真实地形结构无法在地震成像中反映,而且地震成像畸变随着海水深度、震源频率的增加而增大.机理分析表明,中尺度涡所带来的水体温度梯度变化是产生地震成像畸变的主要因素.为了便于工程应用,本文还推导了有效涡强度、温度差与地形畸变率的关系式.本文的研究结果将对提高深海地震成像精度有一定的指导意义.
Combined with seismic simulation methods,the parabolic equation method is used to investigate the distortion of seismic imaging of the target stratum caused by mesoscale eddies.Seismic wave fields for different frequencies and water depth are simulated.It is found that the seismic imaging of the target stratum,due to the perturbation of eddies,does not agree with the original stratum and the distortions increase with the water depth and the frequency.Analyzing the mechanism of distortions,we have concluded that the perturbation of temperature gradient caused by eddies is one of the most important reasons.For the sake of ingineering application,we deduce a relationship among the maximum distorted rate of seismic imaging,the temperature difference and the effective intensity of eddies.The results of this paper could be used to improve the quality of seismic imaging in deep sea.
Combined with seismic simulation methods,the parabolic equation method is used to investigate the distortion of seismic imaging of the target stratum caused by mesoscale eddies.Seismic wave fields for different frequencies and water depth are simulated.It is found that the seismic imaging of the target stratum,due to the perturbation of eddies,does not agree with the original stratum and the distortions increase with the water depth and the frequency.Analyzing the mechanism of distortions,we have concluded that the perturbation of temperature gradient caused by eddies is one of the most important reasons.For the sake of ingineering application,we deduce a relationship among the maximum distorted rate of seismic imaging,the temperature difference and the effective intensity of eddies.The results of this paper could be used to improve the quality of seismic imaging in deep sea.
引文
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[24]Ergin K.Energy ratio of the seismic waves reflected andrefracted at a rock-water boundary.Bull.Seism.Soc.Am.,1952,42(4):349-372.
[25]Hunt J M,Hays E E,Degens E T,et al.Red sea:detailedsurvey of hot-brine areas.Science,1967,56(3774):514-516.
[2]Biescas B,Sallarès V,Pelegr J L,et al.Imaging meddyfinestructure using multichannel seismic reflection data.Geophysical Research Letters,2008,35(11):L11609,doi:10.1029/2008GL033971.
[3]Ruddick B.Sounding out ocean fine structure.Science,2003,301(5634):772-773.
[4]宋海斌,Luis P,王东晓等.海洋中尺度涡与内波的地震图像.地球物理学报,2009,52(11):2775-2780.Song H B,Luis P,Wang D X,et al.Seismic images of oceanmeso-scale eddies and internal waves.Chinese J.Geophys.(in Chinese),2009,52(11):2775-2780.
[5]Wood W T,Holbrook W S,Sen M K,et al.Full waveforminversion of reflection seismic data for ocean temperatureprofiles.Geophysical Research Letters,2008,35(4):L04608,doi:10.1029/2007GL032359.
[6]Pinheiro L M,Song H,Ruddick B,et al.Detailed 2-Dimaging of the Mediterranean outflow and meddies off WIberia from multichannel seismic data.Journal of MarineSystems,2010,79(1-2):89-100.
[7]胡毅,刘怀山,陈坚等.地震海洋学研究进展.地球科学进展,2009,24(10):1094-1104.Hu Y,Liu H S,Chen J,et al.Recent progress in seismicoceanography.Advance in Earth Science(in Chinese),2009,24(10):1094-1104.
[8]宋海斌,董崇志,陈林等.用反射地震方法研究物理海洋—地震海洋学简介.地球物理学进展,2008,23(4):1156-1164.Song H B,Dong C Z,Chen L,et al.Reflection seismicmethods for studying physical oceanography:Introduction ofseismic oceanography.Progress in Geophys(in Chinese),2008,23(4):1156-1164.
[9]Kulkarni R S,Siegmann W L,Collins M D,et al.Nonlinearpulse propagation in shallow-water environments withattenuating and dispersive sediments.Journal Acoust.Soc.Am.,1998,104(3):1356-1362.
[10]Parker C E.Gulf stream rings in the Sargasso Sea.Deep-SeaRes,1971,18:981-993.
[11]Henrick R F,Siegmann W L,Jacobson M J.Generalanalysis of ocean eddy effects for sound transmissionapplications.Journal Acoust.Soc.Am.,1977,62(4):860-870.
[12]Baer R N.Calculations of sound propagation through aneddy.Journa Acoust.Soc.Am.,1980,67(4):1180-1185.
[13]Nysen P A,Power P S.Sound propagation through an EastAustralian Current eddy.Journal Acoust.Soc.Am.,1978,63(5):1381-1388.
[14]Jian Y J,Zhang J,Liu Q S,et al.Effect of mesoscale eddieson underwater sound propagation.Applied Acoustics,2009,70(3):432-440.
[15]Krahmann G,Brandt P,Klaeschen D,et al.Mid-depthinternal wave energy off the Iberian Peninsula estimated fromseismic reflection data.J.Geophys.Res,2008,113(C12):C12016,doi:10.1029/2007JC00467.
[16]Nakamura Y,Noguchi T,Tsuji T,et al.Simultaneousseismic reflection and physical oceanographic observations ofoceanic fine structure in the Kuroshio extension front.Geophys.Res.Lett.,2006,33(23):L23605,doi:10.1029/2006GL027437.
[17]Kormann J,Cobo P,Prieto A.Perfectly matched layers formodelling seismic oceanography experiments.Journal ofSound and Vibration,2008,317(1-2):354-365.
[18]Robertson J S,Siegmann W L,Jacobson M J.Current andcurrent shear effects in the parabolic approximation forunderwater sound channels.J.Acoust.Soc.Am.,1985,77(5):1768-1780.
[19]Godin O A.Parabolic approximation in the theory of thesound propagation in Three-Dimensionally heterogeneousmedia.Doklady Physics,2000,45(8):367-371.
[20]Jerzak W,Collins M D,Evans R B,et al.Parabolic equationtechniques for seismic waves.Pure and Applied Geophysics,2002,159(7-8):1681-1689.
[21]Collis J M,Siegmann W L,Jensen F B,et al.Parabolicequation solution of seismo-acoustics problems involvingvariations in bathymetry and sediment thickness.J.Acoust.Soc.Am.,2008,123(1):51-55.
[22]吴培木,郭小钢,吴日升.台湾省恒春西南海域声速场分析.台湾海峡,2001,20(3):279-286.Wu P M,Guo X G,Wu R S.Analyses of sound velocity fieldin southwest sea area off Hengchun of Taiwan.J.Oceanogr.Taiwan Strait.(in Chinese),2001,20(3):279-286.
[23]Eckart C.Properties of Water.2.The equation of state ofwater and sea water at low temperatures and pressures.Am.J.Sci,1958,256:225-240.
[24]Ergin K.Energy ratio of the seismic waves reflected andrefracted at a rock-water boundary.Bull.Seism.Soc.Am.,1952,42(4):349-372.
[25]Hunt J M,Hays E E,Degens E T,et al.Red sea:detailedsurvey of hot-brine areas.Science,1967,56(3774):514-516.
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