利用远震接收函数方法研究南海西沙群岛下方地壳结构
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摘要
利用西沙琛航岛流动地震台站和水兴岛固定地震台站的资料,提取了远震P波接收函数,结合正演和反演方法模拟了台站下方的地壳结构.模拟结果显示:西沙群岛地壳顶部存在2 km厚的新生代低速沉积层,横波速度只有2.0～2.2 km/s;上地壳为一速度梯度带,横波速度由2 km处的3.4 km/s逐渐增加到1 2 km深度时的3.8 km/s;下地壳存在明显低速层,厚度达到12 km,平均横波速度3.5 km/s;莫霍面埋深26～28 km,也表现为一速度梯度带,横波速度从3.8 km/s变化到4.6 km/s左右,并保持稳定:该地区的地壳泊松比值大于0.3,推测西沙群岛的壳内低速层和异常泊松比值与地幔热活动引起的韧性流变构造和岩石矿物的各向异性排列有关.
1-D shear wave velocity models for the crust structure beneath the Xisha Islands of the South China Sea are constructed using the data from a temporary seismic station at Chenhang island(CHH) and a permanent seismic station at Yongxing island(YXN).Receiver functions for each station were obtained from teleseismic records with clear P waveforms and a combination of inversion and forward modeling was used to infer the crustal structure below each station. Modeling results show that a 2 km thick low-velocity layer with shear wave velocity of 2.0 km/s exists on the top of crust.It is attributed to carbonate sediments in this area.Upper crust is a velocity gradient zone in which the shear wave velocity gradually increases from 3.4 km/s at the depth of 2 km to 3.8 km/s at the depth of 12 km.Lower crust is 12 km thick and has a prominent low shear wave velocity of 3.5 km/s.The Moho lies at the depth of 26～28 km and also has a velocity gradient zone with shear wave velocity changing from 3.8 km/s to 4.6 km/s.The Poisson s ratio shows a higher value greater than 0.3.We suggest that the low-velocity layer in lower crust and the anomalous Poisson s ratio result from the presence of anisotropy of rocks and minerals which arises from the ductile rheological zone and hot mantle activity in the depth.
1-D shear wave velocity models for the crust structure beneath the Xisha Islands of the South China Sea are constructed using the data from a temporary seismic station at Chenhang island(CHH) and a permanent seismic station at Yongxing island(YXN).Receiver functions for each station were obtained from teleseismic records with clear P waveforms and a combination of inversion and forward modeling was used to infer the crustal structure below each station. Modeling results show that a 2 km thick low-velocity layer with shear wave velocity of 2.0 km/s exists on the top of crust.It is attributed to carbonate sediments in this area.Upper crust is a velocity gradient zone in which the shear wave velocity gradually increases from 3.4 km/s at the depth of 2 km to 3.8 km/s at the depth of 12 km.Lower crust is 12 km thick and has a prominent low shear wave velocity of 3.5 km/s.The Moho lies at the depth of 26～28 km and also has a velocity gradient zone with shear wave velocity changing from 3.8 km/s to 4.6 km/s.The Poisson s ratio shows a higher value greater than 0.3.We suggest that the low-velocity layer in lower crust and the anomalous Poisson s ratio result from the presence of anisotropy of rocks and minerals which arises from the ductile rheological zone and hot mantle activity in the depth.
引文
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[11]Owens T J,Taylor S R,Randall G.Crustal structure at Regional Seismic Test Network stations determined from ??inversion of broadband teleseismic P waveforms.Bulletin of the Seismological Society of America,1987,77(2):631- 662
[12]刘启元,Rainer K,李顺成.中国数字地震台网的接收函数及其非线性反演.地球物理学报,1997,40(3):356-368 Liu Q Y,Rainer K,Li S C.Receiver functions at the stations of the Chinese digital seismic network(CDSN) and their nonlinear inversion.Chinese J.Geophys.(in Chinese),1997,40 (3):356-368
[13]Yuan X,Sobolev S V,Onchen O,et al.Subduction and collision processes in the Central Andes constrained by converted seismic phases.Nature,2000,408(6815):958- 961
[14]Qiu X L,Priestley K,McKenzie D.Teleseismic P-waveform receiver function analysis and its application to Qiongzhong station(QIZ) of Hainan Island,NW South China Sea. Journal of Geosciences of China,2002,4(1):1-8
[15]Ammon C J,Randall G E,Zandt G.On the non-uniqueness of receiver function inversions.Journal of Geophysical Research,1990,9S(B10):15303-15318
[16]Langston C A.Structure under Mount Rainier,Washington, inferred from teleseismic body waves.Journal of Geophysical Research,1979,84(B9):4749-4762
[17]Owens T J,Crosson R S.Shallow structure effects on broadband teleseismic P waveforms.Bulletin of the Seismological Society of America,1988,78(1):96-108
[18]Cassidy J F.Numerical experiments in broadband receiver function analysis.Bulletin of the Seismological Society of America,1992,82(3):1453-1474
[19]Zhu L P,Kanamori H.Moho depth variation in southern California from teleseismic receiver functions.Journal of Geophysical Research,2000,105(B2):2969-2980
[20]陈九辉.远震体波接收函数方法:理论与应用[博士论文].北京:中国地震局地质研究所,2007 Chen J H.Teleseismic receiver function:theory and applications [Ph.D.thesis](in Chinese).Beijing:Institute of Geology, China Earthquake Administration,2007
[21]王玉净,勾韵娴,章炳高等.西沙群岛西琛—井中新世地层、古生物群和古环境研究.微体古生物学报,1996,13(3): 215-223 Wang Y J,Gou Y X,Zhang B G,et al.Studies of Miocene Strata,Biota and Palaeoenvironment from Xi-Chen No.1 Hole in Xisha Islands.Acta Micropalaeontologica Sinica(in Chinese),1996,13(3):215-223
[22]张明书,刘健,李绍全等.西沙群岛西琛一井礁序列成岩作用研究.地质学报,1997,71(3):236-244 Zhang M S,Liu J,Li S Q,et al.Diagenesis of the reef succession in the Xisha Islands.Acta Geologica Sinica(in Chinese),1997,71(3):236-244
[23]Gutenberg B.Channel waves in the Earth's crust.Geophysics, 1955,20(2):283-291
[24]Wang C Y,Lou H,Lu Z Y,et al.S-wave crustal and upper mantle's velocity structure in the eastern Tibetan Plateau-Deep environment of lower crustal flow.Science China Earth Sciences,2008,51(2):263-274
[25]Xu Y,Li Z W,Huang R Q,et al.Seismic structure of the Longmen Shan region from S-wave tomography and its relationship with the Wenchuan M_s8.0 earthquake on 12 May 2008,southwestern China.Geophysical Research Letters, 2010,37:1-6
[26]Brodic K,Rutter R H.Deep crustal extensional faulting in the Ivrea zone of Northern Italy.Tectonophysics,1987,140 (2-4):193-212
[27]Christensen N I,Mooney W D.Seismic velocity structure and composition of the continental crust:A global view. Journal of Geophysical Research,1995,100(B6):9761- 9788
[28]Zhang Z J,Badal J,Li Y K,et al.Crust upper mantle seismic velocity structure across Southeastern China. Tectonophysics,2005,395(1-2):137-157
[29]Zhao M H,Qiu X L,Xu H L,et al.Distribution and identification of the low-velocity layer in the northern South China Sea Progress in Natural Science,2007,17(5):591-600
[30]Wei B Z,Chung W Y.Strike-slip faulting on the northern margin of the South China Sea:evidence from two earthquakes offshore of Hainan Island,China,in December 1969. Tectonophysics,1995,241(1-2):55-66
[31]Wissmann G,Kudrass H,Hinz K.Continuing rifting on the South China margin.Geowissenschaften,1996,16(7-8):310- 312
[32]Shi X B,Qiu X L,Xia K Y,et al.Characteristics of surface heat flow in the South China Sea.Journal of Asian Earth Science,2003,22(3):265-277
[33]Shi X,Zhou D,Qiu X,et al.Thermal and rheological structures of the Xisha Trough,South China Sea.Tectonophysics, 2002,351(4):285-300
[34]Ji S C,Wang Q,Salisbury M H.Composition and tectonic evolution of the Chinese continental crust constrained by Poisson's ratio.Tectonophysics,2009,463(1-4):15-30
[35]McNamara D E,Owens T J.Azimuthal shear wave velocity anisotropy in the Basin and Range Province using Moho Ps converted phases.Journal of Geophysical Research,1993, 98(B7):12003-12017
[2]金庆焕.南海地质与油气资源.北京:地质出版社,1989 Jin Q H.Geology and Hydrocarbon Resources in the South China Sea(in Chinese).Beijing:Geological Publishing House, 1989
[3]孙嘉诗.西沙基底形成时代的商榷.海洋地质与第四纪地质,1987,7(4):5-6 Sun J S.A discussion on the formation ages of the bedrock in the Xisha Islands.Marine Geology & Quaternary Geology (in Chinese),1987,7(4):5-6
[4]姚伯初.南海北部陆缘的地壳结构及构造意义.海洋地质与第四纪地质,1998,18(2):1-16 Yao B C.Crust structure of the northern margin of the South China Sea and its tectonic significance.Marine Geology & Quaternary Geology(in Chinese),1998,18(2):1-16
[5]Qiu X L,Ye S Y,Wu S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea. Tectonophysics,2001,341(1):179-193
[6]Yan P,Zhou D,Liu Z S.A crustal structure profile across the northern continental margin of the South China Sea. Tectonophysics,2001,338(1):1-21
[7]丘学林,曾钢平,胥颐等.南海西沙石岛地震台下的地壳结构研究.地球物理学报,2006,49(6):1720-1729 Qiu X L,Zeng G P,Xu Y,et al.The crustal structure beneath the Shidao Station on Xisha Islands of South China Sea.Chinese J.Geophys.(in Chinese),2006,49(6):1720- 1729
[8]阮爱国,李家彪,郝天姚等.石岛地震台远震记录反演研究.海洋学报,2006,28(2):85-91 Ruan AG,Li J B,Hao T Y,et al.Inversion of far-field seismic waves at Shidao Seismographic Station.Acta Oceanologica Sinica(in Chinese),2006,28(2):85-91
[9]刘建华,吴华,刘福田.华南及其海域三维速度分布特征与岩石层结构.地球物理学报,1996,39(4):483-492 Liu J H,Wu H,Liu F T.Features of 3-D velocity distribution and lithosphere structure in South China and its contiguous sea area.Chinese J.Geophys.(Acta Geophysica Sinica)(in Chinese),1996,39(4):483-492
[10]胥颐,刘建华,傅竹武等.西沙群岛和哀牢山—红河地区的宽频带地震观测.热带海洋学报,2003,22(2):83-88 Xu Y,Liu J H,Fu Z W,et al.Broadband earthquake observation in Xisha Islands and Ailao Shan-Red River region.Journal of Tropical Oceanography(in Chinese), 2003,22(2):83-88
[11]Owens T J,Taylor S R,Randall G.Crustal structure at Regional Seismic Test Network stations determined from ??inversion of broadband teleseismic P waveforms.Bulletin of the Seismological Society of America,1987,77(2):631- 662
[12]刘启元,Rainer K,李顺成.中国数字地震台网的接收函数及其非线性反演.地球物理学报,1997,40(3):356-368 Liu Q Y,Rainer K,Li S C.Receiver functions at the stations of the Chinese digital seismic network(CDSN) and their nonlinear inversion.Chinese J.Geophys.(in Chinese),1997,40 (3):356-368
[13]Yuan X,Sobolev S V,Onchen O,et al.Subduction and collision processes in the Central Andes constrained by converted seismic phases.Nature,2000,408(6815):958- 961
[14]Qiu X L,Priestley K,McKenzie D.Teleseismic P-waveform receiver function analysis and its application to Qiongzhong station(QIZ) of Hainan Island,NW South China Sea. Journal of Geosciences of China,2002,4(1):1-8
[15]Ammon C J,Randall G E,Zandt G.On the non-uniqueness of receiver function inversions.Journal of Geophysical Research,1990,9S(B10):15303-15318
[16]Langston C A.Structure under Mount Rainier,Washington, inferred from teleseismic body waves.Journal of Geophysical Research,1979,84(B9):4749-4762
[17]Owens T J,Crosson R S.Shallow structure effects on broadband teleseismic P waveforms.Bulletin of the Seismological Society of America,1988,78(1):96-108
[18]Cassidy J F.Numerical experiments in broadband receiver function analysis.Bulletin of the Seismological Society of America,1992,82(3):1453-1474
[19]Zhu L P,Kanamori H.Moho depth variation in southern California from teleseismic receiver functions.Journal of Geophysical Research,2000,105(B2):2969-2980
[20]陈九辉.远震体波接收函数方法:理论与应用[博士论文].北京:中国地震局地质研究所,2007 Chen J H.Teleseismic receiver function:theory and applications [Ph.D.thesis](in Chinese).Beijing:Institute of Geology, China Earthquake Administration,2007
[21]王玉净,勾韵娴,章炳高等.西沙群岛西琛—井中新世地层、古生物群和古环境研究.微体古生物学报,1996,13(3): 215-223 Wang Y J,Gou Y X,Zhang B G,et al.Studies of Miocene Strata,Biota and Palaeoenvironment from Xi-Chen No.1 Hole in Xisha Islands.Acta Micropalaeontologica Sinica(in Chinese),1996,13(3):215-223
[22]张明书,刘健,李绍全等.西沙群岛西琛一井礁序列成岩作用研究.地质学报,1997,71(3):236-244 Zhang M S,Liu J,Li S Q,et al.Diagenesis of the reef succession in the Xisha Islands.Acta Geologica Sinica(in Chinese),1997,71(3):236-244
[23]Gutenberg B.Channel waves in the Earth's crust.Geophysics, 1955,20(2):283-291
[24]Wang C Y,Lou H,Lu Z Y,et al.S-wave crustal and upper mantle's velocity structure in the eastern Tibetan Plateau-Deep environment of lower crustal flow.Science China Earth Sciences,2008,51(2):263-274
[25]Xu Y,Li Z W,Huang R Q,et al.Seismic structure of the Longmen Shan region from S-wave tomography and its relationship with the Wenchuan M_s8.0 earthquake on 12 May 2008,southwestern China.Geophysical Research Letters, 2010,37:1-6
[26]Brodic K,Rutter R H.Deep crustal extensional faulting in the Ivrea zone of Northern Italy.Tectonophysics,1987,140 (2-4):193-212
[27]Christensen N I,Mooney W D.Seismic velocity structure and composition of the continental crust:A global view. Journal of Geophysical Research,1995,100(B6):9761- 9788
[28]Zhang Z J,Badal J,Li Y K,et al.Crust upper mantle seismic velocity structure across Southeastern China. Tectonophysics,2005,395(1-2):137-157
[29]Zhao M H,Qiu X L,Xu H L,et al.Distribution and identification of the low-velocity layer in the northern South China Sea Progress in Natural Science,2007,17(5):591-600
[30]Wei B Z,Chung W Y.Strike-slip faulting on the northern margin of the South China Sea:evidence from two earthquakes offshore of Hainan Island,China,in December 1969. Tectonophysics,1995,241(1-2):55-66
[31]Wissmann G,Kudrass H,Hinz K.Continuing rifting on the South China margin.Geowissenschaften,1996,16(7-8):310- 312
[32]Shi X B,Qiu X L,Xia K Y,et al.Characteristics of surface heat flow in the South China Sea.Journal of Asian Earth Science,2003,22(3):265-277
[33]Shi X,Zhou D,Qiu X,et al.Thermal and rheological structures of the Xisha Trough,South China Sea.Tectonophysics, 2002,351(4):285-300
[34]Ji S C,Wang Q,Salisbury M H.Composition and tectonic evolution of the Chinese continental crust constrained by Poisson's ratio.Tectonophysics,2009,463(1-4):15-30
[35]McNamara D E,Owens T J.Azimuthal shear wave velocity anisotropy in the Basin and Range Province using Moho Ps converted phases.Journal of Geophysical Research,1993, 98(B7):12003-12017
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