海水物性对地震反射系数的相对贡献
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摘要
地震剖面与海水物性之间的关系是地震海洋学亟待研究的关键问题之一.本文选取地中海涡旋、各大洋不同纬度和南海东北部不同月份的三组CTD资料,按海域、季节和深度对法向相对贡献进行计算和分析,并从地中海涡旋CTD资料中选取典型温盐界面进行非法向相对贡献的研究.结果表明声速和温度的平均法向相对贡献随着海域、季节和深度呈相似性变化,其变化范围主要由相邻海水团之间的物性差异决定,分别为78%～94%和74%～98%.声速和温度(密度和盐度)的非法向相对贡献随着入射角的增加而增大(减小).用于反演的叠前地震数据应尽量包含较宽入射角范围的道集,特别是对于相对贡献较小的密度和盐度,包含小入射角的地震道对提高反演结果的精度尤为重要.通过对比地中海涡旋的Turner角剖面和相对贡献结果,发现Turner角对相对贡献具有很好的指示作用,其密度和盐度相对贡献较大的区域对应于Turner角为-45°的双稳定区域与扩散对流区域的边界附近,在此区域的密度比为零或较小.南北极附近海域的密度比较小,从而导致高纬度站位出现声速和温度相对贡献偏小的现象.南海东北部冬季表层海水的温度和声速相对贡献偏大则可能是由于黑潮侵入导致海水层温度差异及密度比变大引起.
The relation between seismic profile and seawater physical property is one of the key problems urgent to be studied in seismic oceanography. This paper choose three groups of CTD data, including the section of Meddy, ten stations at different latitudes of the oceans, monthly data in the northeastern South China Sea, to study the normal and non-normal relative contribution according to the sea area, season and depth of water. The results show that the average normal relative contributions of sound speed and temperature similarly vary with sea area, season and water depth in a range of 78%~94% and 74%~98% respectively, mainly determined by the physical differences between adjacent water masses. The non-normal relative contributions of sound speed and temperature are enhanced with the increasing incidence angle, but the relative contributions of density and salinity are opposite. The prestack seismic data for inversion should contain gathers with a wide range of incidence angles. It is especially important to contain seismic traces with small incidence angle to improve the accuracy of density and salinity inversion which have smaller relative contribution. Through comparing the relative contribution of Meddy with the Turner angle section, it is found that Turner angle has an excellent indicative function to relative contribution. The zone, where the relative contributions of density and salinity are larger, well corresponds to the boundary between double stable region and diffusive region, where Turner angle is about -45°. The density ratios are relatively small at high latitude stations which result in small relative contribution of sound speed and temperature. The relative contributions of sound speed and temperature are slightly larger in the surface seawater in the northeastern South China Sea. This may be caused by temperature difference and density ratio increasing due to the Kuroshio intrusion.
The relation between seismic profile and seawater physical property is one of the key problems urgent to be studied in seismic oceanography. This paper choose three groups of CTD data, including the section of Meddy, ten stations at different latitudes of the oceans, monthly data in the northeastern South China Sea, to study the normal and non-normal relative contribution according to the sea area, season and depth of water. The results show that the average normal relative contributions of sound speed and temperature similarly vary with sea area, season and water depth in a range of 78%~94% and 74%~98% respectively, mainly determined by the physical differences between adjacent water masses. The non-normal relative contributions of sound speed and temperature are enhanced with the increasing incidence angle, but the relative contributions of density and salinity are opposite. The prestack seismic data for inversion should contain gathers with a wide range of incidence angles. It is especially important to contain seismic traces with small incidence angle to improve the accuracy of density and salinity inversion which have smaller relative contribution. Through comparing the relative contribution of Meddy with the Turner angle section, it is found that Turner angle has an excellent indicative function to relative contribution. The zone, where the relative contributions of density and salinity are larger, well corresponds to the boundary between double stable region and diffusive region, where Turner angle is about -45°. The density ratios are relatively small at high latitude stations which result in small relative contribution of sound speed and temperature. The relative contributions of sound speed and temperature are slightly larger in the surface seawater in the northeastern South China Sea. This may be caused by temperature difference and density ratio increasing due to the Kuroshio intrusion.
引文
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[13]董崇志,宋海斌,郝天珧等.南海东北部海洋内波的反射地震研究.地球物理学报,2009,52(8):2050-2055,doi:10.3969/j.issn.00015733.2009.08.013.Dong C Z,Song H B,Hao T Y,et al.Studying of oceanicinternal wave spectra in the Northeast South China Sea fromseismic reflections.Chinese J.Geophys.(in Chinese),2009,52(8):2050-2055,doi:10.3969/j.issn.00015733.2009.08.013.
[14]宋海斌,拜阳,董崇志等.南海东北部内波特征——经验模态分解方法应用初探.地球物理学报,2010,53(2):393-400,doi:10.3969/j.issn.0001-5733.2010.02.001.Song H B,Bai Y,Dong C Z,et al.A preliminary study ofapplication of Empirical Mode Decomposition method inunderstanding the features of internal waves in thenortheastern South China Sea.Chinese J.Geophys.(inChinese),2010,53(2):393-400,doi:10.3969/j.issn.0001-5733.2010.02.001.
[15]Fer I,Nandi P,Holbrook W S,et al.Seismic imaging of athermohaline staircase in the western tropical Atlantic.OceanScience,2010,6(3):621-631.
[16]Ambar I,Bezerra R,Pinheiro L M,et al.Thermohalinestaircases viewed by contemporaneous seismic imaging.1stESF.Exploratory Workshop on Seismic Oceanography.November,19-21,2008.Begur,Girona(Spain)http://www.cmima.csic.es/files/sow/IAmbar.pdf,2008.
[17]Páramo P,Holbrook W S.Temperature contrasts in thewater column inferred from amplitude-versus-offset analysisof acoustic reflections.Geophys.Res.Lett.,2005,32(24):L24611,doi:10.1029/2005GL024533.
[18]Wood W T,Holbrook W S,Sen M K,et al.Full waveforminversion of reflection seismic data for ocean temperatureprofiles.Geophys.Res.Lett.,2008,35(4):L04608,doi:10.1029/2007GL032359.
[19]Sheen K L,White N J,Hobbs R W.Estimating mixing ratesfrom seismic images of oceanic structure.Geophys.Res.Lett.,2009,36(24):L00D04,doi:10.1029/2009GL040106.
[20]Millero F J,Chen C T,Bradshaw A,et al.A new highpressure equation of state for seawater.Deep Sea Res.,1980,27(3-4):255-264.
[21]Fofonoff N P,Millard R C Jr.Algorithms for Computation ofFundamental Properties of Seawater.Greenberg:UnescoTech.Pap.in Mar.Sci.,1983.
[22]Ruddick B,Song H B,Dong C Z,et al.Water column seismicimages as maps of of temperature gradient.Oceanography,2009,22(1):192-205.
[23]Sallarès V,Biescas B,Buffett G,et al.Relative contributionof temperature and salinity to ocean acoustic reflectivity.Geophys.Res.Lett.,2009,36(24):L00D06,doi:10.1029/2009GL040187.
[24]殷八斤,曾灏,杨在岩.AVO技术的理论与实践.北京:石油工业出版社,1995.Yin B J,Zeng H,Yang Z Y.Theory and Practice of AVOTechnology(in Chinese).Beijing:Petroleum IndustryPress,1995.
[25]Aki K,Richards P G.Quantitative Seismology-Theory andMethods.San Francisco:W.H.Freeman and Co.,1980.
[26]Armi L,Hebert D,Oakey N,et al.Two years in the life ofa Mediterranean salt lens.J.Phys.Oceanogr.,1989,19(3):354-370.
[27]Ruddick B.A practical indicator of the stability of the watercolumn to double-diffusive activity.Deep Sea Res.,1983,30(10):1105-1107.
[28]Su J L.Overview of the South China Sea circulation and itsinfluence on the coastal physical oceanography outside thePearl River Estuary.Continental Shelf Research,2004,24(16):1745-1760.
[29]Liu Q Y,Kaneko A,Su J L.Recent progress in studies ofthe South China Sea Circulation.J.Oceanogr.,2008,64(5):753-762.
[30]胡筱敏,熊学军,乔方利等.利用漂流浮标资料对黑潮及其邻近海域表层流场及其季节分布特征的分析研究.海洋学报,2008,30(6):1-16.Hu X M,Xiong X J,Qiao F L,et al.Surface current fieldand seasonal variability in the Kuroshio and adjacent regionsderived from satellite-tracked drifter data.Acta OceanologicaSinica(in Chinese),2008,30(6):1-16.
[31]鲍献文,鞠霞,吴德星.吕宋海峡120°E断面水交换特征.中国海洋大学学报(自然科学版),2009,39(1):1-6,76.Bao X W,Ju X,Wu D X.Characteristics of water exchangeacross 120oE Section in the Luzon Strait.Period.OceanUniv.China(in Chinese),2009,39(1):1-6,76.
[32]Tian J W,Yang Q X,Zhao W.Enhanced diapycnal mixing inthe South China Sea.J.Phys.Oceanogr.,2009,39(12):3191-3203.
[2]Nandi P,Holbrook W S,Pearse S,et al.Seismic reflectionimaging of water mass boundaries in the Norwegian Sea.Geophys.Res.Lett.,2004,31(23):L23321,doi:10.1029/2004GL021325.
[3]Tsuji T,Noguchi T,Niino H,et al.Two-dimensionalmapping of fine structures in the Kuroshio Current usingseismic reflection data.Geophys.Res.Lett.,2005,32(14):L14609,doi:10.1029/2005GL023095.
[4]Noguchi T,Niino H,Nakamura Y,et al.Thermohalineinterleaving in the Kuroshio Extension Front:Seismicreflection imagery and in situ measurements.In:Eos Trans.AGU,Ocean Sci.Meet.,Suppl.,Abstract,2006,87(36):OS14I-06.
[5]White N,Koenitz D,Hobbs R.Seismic imaging of theAntarctic Circumpolar Current near Drake Passage.In:EosTrans.AGU,Ocean Sci.Meet.,Suppl.,Abstract,2006,87(36):OS14I-04.
[6]Pinheiro L M,Song H B,Ruddick B R,et al.Detailed 2-Dimaging of the Mediterranean Outflow and Meddies off WIberia from multichannel seismic data.In:Eos Trans.AGU,Ocean Sci.Meet.,Suppl.,Abstract,2006,87(36):OS13I-02.
[7]Klaeschen D,Papenberg C,Reston T,et al.Seismic imagesand properties of a Meddy.In:Eos Trans.AGU,Ocean Sci.Meet.,Suppl.,Abstract,2006,87(36):OS13I-03.
[8]Biescas B,Sallares V,Pelegri J L,et al.Imaging meddyfinestructure using multichannel seismic reflection data.Geophys.Res.Lett.,2008,35(11):L11609,doi:10.1029/2008GL033971.
[9]Pinheiro L M,Song H B,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,doi:10.1016/j.jmarsys.2009.07.004.
[10]宋海斌,Pinheiro L M,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,doi:10.3969/j.issn.0001-5733.2009.11.012.Song H B,Pinheiro L M,Wang D X,et al.Seismic imagesof ocean meso-scale eddies and internal waves.Chinese J.Geophys.(in Chinese),2009,52(11):2775-2780,doi:10.3969/j.issn.0001-5733.2009.11.012.
[11]Holbrook W S,Fer I.Ocean internal wave spectra inferredfrom seismic reflection transects.Geophys.Res.Lett.,2005,32(15):L15604,doi:10.1029/2005GL023733.
[12]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:10.1029/2007JC004678.
[13]董崇志,宋海斌,郝天珧等.南海东北部海洋内波的反射地震研究.地球物理学报,2009,52(8):2050-2055,doi:10.3969/j.issn.00015733.2009.08.013.Dong C Z,Song H B,Hao T Y,et al.Studying of oceanicinternal wave spectra in the Northeast South China Sea fromseismic reflections.Chinese J.Geophys.(in Chinese),2009,52(8):2050-2055,doi:10.3969/j.issn.00015733.2009.08.013.
[14]宋海斌,拜阳,董崇志等.南海东北部内波特征——经验模态分解方法应用初探.地球物理学报,2010,53(2):393-400,doi:10.3969/j.issn.0001-5733.2010.02.001.Song H B,Bai Y,Dong C Z,et al.A preliminary study ofapplication of Empirical Mode Decomposition method inunderstanding the features of internal waves in thenortheastern South China Sea.Chinese J.Geophys.(inChinese),2010,53(2):393-400,doi:10.3969/j.issn.0001-5733.2010.02.001.
[15]Fer I,Nandi P,Holbrook W S,et al.Seismic imaging of athermohaline staircase in the western tropical Atlantic.OceanScience,2010,6(3):621-631.
[16]Ambar I,Bezerra R,Pinheiro L M,et al.Thermohalinestaircases viewed by contemporaneous seismic imaging.1stESF.Exploratory Workshop on Seismic Oceanography.November,19-21,2008.Begur,Girona(Spain)http://www.cmima.csic.es/files/sow/IAmbar.pdf,2008.
[17]Páramo P,Holbrook W S.Temperature contrasts in thewater column inferred from amplitude-versus-offset analysisof acoustic reflections.Geophys.Res.Lett.,2005,32(24):L24611,doi:10.1029/2005GL024533.
[18]Wood W T,Holbrook W S,Sen M K,et al.Full waveforminversion of reflection seismic data for ocean temperatureprofiles.Geophys.Res.Lett.,2008,35(4):L04608,doi:10.1029/2007GL032359.
[19]Sheen K L,White N J,Hobbs R W.Estimating mixing ratesfrom seismic images of oceanic structure.Geophys.Res.Lett.,2009,36(24):L00D04,doi:10.1029/2009GL040106.
[20]Millero F J,Chen C T,Bradshaw A,et al.A new highpressure equation of state for seawater.Deep Sea Res.,1980,27(3-4):255-264.
[21]Fofonoff N P,Millard R C Jr.Algorithms for Computation ofFundamental Properties of Seawater.Greenberg:UnescoTech.Pap.in Mar.Sci.,1983.
[22]Ruddick B,Song H B,Dong C Z,et al.Water column seismicimages as maps of of temperature gradient.Oceanography,2009,22(1):192-205.
[23]Sallarès V,Biescas B,Buffett G,et al.Relative contributionof temperature and salinity to ocean acoustic reflectivity.Geophys.Res.Lett.,2009,36(24):L00D06,doi:10.1029/2009GL040187.
[24]殷八斤,曾灏,杨在岩.AVO技术的理论与实践.北京:石油工业出版社,1995.Yin B J,Zeng H,Yang Z Y.Theory and Practice of AVOTechnology(in Chinese).Beijing:Petroleum IndustryPress,1995.
[25]Aki K,Richards P G.Quantitative Seismology-Theory andMethods.San Francisco:W.H.Freeman and Co.,1980.
[26]Armi L,Hebert D,Oakey N,et al.Two years in the life ofa Mediterranean salt lens.J.Phys.Oceanogr.,1989,19(3):354-370.
[27]Ruddick B.A practical indicator of the stability of the watercolumn to double-diffusive activity.Deep Sea Res.,1983,30(10):1105-1107.
[28]Su J L.Overview of the South China Sea circulation and itsinfluence on the coastal physical oceanography outside thePearl River Estuary.Continental Shelf Research,2004,24(16):1745-1760.
[29]Liu Q Y,Kaneko A,Su J L.Recent progress in studies ofthe South China Sea Circulation.J.Oceanogr.,2008,64(5):753-762.
[30]胡筱敏,熊学军,乔方利等.利用漂流浮标资料对黑潮及其邻近海域表层流场及其季节分布特征的分析研究.海洋学报,2008,30(6):1-16.Hu X M,Xiong X J,Qiao F L,et al.Surface current fieldand seasonal variability in the Kuroshio and adjacent regionsderived from satellite-tracked drifter data.Acta OceanologicaSinica(in Chinese),2008,30(6):1-16.
[31]鲍献文,鞠霞,吴德星.吕宋海峡120°E断面水交换特征.中国海洋大学学报(自然科学版),2009,39(1):1-6,76.Bao X W,Ju X,Wu D X.Characteristics of water exchangeacross 120oE Section in the Luzon Strait.Period.OceanUniv.China(in Chinese),2009,39(1):1-6,76.
[32]Tian J W,Yang Q X,Zhao W.Enhanced diapycnal mixing inthe South China Sea.J.Phys.Oceanogr.,2009,39(12):3191-3203.
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