南海瑞雷面波群速度层析成像及其地球动力学意义
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摘要
南海处于欧亚板块、菲律宾海板块、太平洋板块和印度-澳大利亚板块的交汇处,其地质和构造作用十分复杂.通过面波群速度成像,给出了南海及邻区的三维横波速度分布并分析了其地球动力学意义.南海西部和南部新布设的地震台站使得利用单台法时路径覆盖比过去更好.特别是在华南地区,新的台站分布能够弥补该地区地震少且台站少造成的射线密度不够的缺点.首先运用多重滤波法得到南海周边48个台站周期为14—130s范围内的基阶瑞雷波频散曲线图;接着通过子空间反演得到整个区域在不同周期时的群速度分布;最后通过阻尼最小二乘反演得到不同深度切片上的横波速度分布及不同纵剖面上的横波速度分布.结果显示:①海盆速度较高,且速度分布很好地勾勒出海盆的轮廓.浅层较高的横波速度说明海盆都具有洋壳性质,而深部较高的横波速度则可能对应扩张中心生成洋壳后残留的高速物质.不同海盆速度上的差异与它们的热流值和年龄大小一致.海盆下的高速异常在60km以下消失,且在一定深度范围内由低速区替代.在低速区下200km深度,在南海海盆观测到一条NE--SW走向的高速异常,可能与古俯冲带有关.②环南海出现明显的高速区,对应俯冲带特征,且这些高速区速度差异明显且有间断,说明俯冲带的非均质性和俯冲角度的差异.③在环南海高速区内侧(向南海侧)观测到不连续的低速区.在浅层,这些低速区反映了沉积层和地壳的厚度特征.在地幔,这些低速区可能对应于古太平洋俯冲带的地幔楔或者也可能反映了南海海盆停止扩张后残留的地幔熔融物质.④南海海盆岩石圈的厚度为60—85km.
The South China Sea is one of the marginal seas of West Pacific where the Eurasian plate,Philippine Sea plate,Pacific plate and Indo-Australian plate interact,and therefore has complex geological structures.In this study,we give a 3D shear wave velocity structure of South China Sea deduced from surface wave tomography and analyze its geodynamic implications.Due to the newly deployed seismic stations in western and southern South China Sea,we have a better ray path coverage when using the single station method.This is especially true for the coastal region of southern China,where earthquakes occur less frequently and the newly added stations can increase the ray density in this region.We used earthquakes distributed on the periphery of South China Sea and collected earthquake data from 48 stations.We first calculated the group velocity dispersion curves of fundamental mode for Rayleigh waves with periods from 14 s to 130 s using multiple filter technique.Then we conducted subspace inversion to get group velocity distributions for different periods in the region.Finally,on the basis of the relationship between shear wave velocity and group velocity under certain layer structure of the Earth,we obtained the 3D shear wave structures in the form of depth slices and vertical profiles by using a damped least square algorithm.The results show:① High velocities exist in sea basins where velocity image delineates the shape of sea basins:the high velocities in shallow parts may indicate oceanic characteristics of the sea basin crust,while high velocities in deeper parts may come from high velocity materials which remained after the formation of oceanic crust at expanding ocean ridge.The velocity differences among sea basins are consistent with their heat flow values as well as their ages.The high velocities disappear at depths greater than 60 km,and are replaced by a low-velocity zone in a certain depth range.Beneath the low-velocity zone,a NE--SW high-velocity belt is observed at a depth of 200 km,and may be related to the ancient subduction in this region.② Surrounding the South China Sea,there are obvious high velocities representing peripheral subductions.These high-velocity features are segmented and show differences in velocity values,implying nonuniformness of these subducting plates as well as their different subducting angles.③ Above these high-velocities,we see discontinuous low-velocity zones.At shallow depths,these low velocities reflect the thickness of sedimentary layers and the crust,and in mantle depths,the low velocities may correspond to either mantle wedges of the ancient Pacific subduction zones or residual mantle melting anomalies after the cease of South China Sea opening.④ The lithosphere thickness of the South China Sea basin tends to be 60—85 km.
The South China Sea is one of the marginal seas of West Pacific where the Eurasian plate,Philippine Sea plate,Pacific plate and Indo-Australian plate interact,and therefore has complex geological structures.In this study,we give a 3D shear wave velocity structure of South China Sea deduced from surface wave tomography and analyze its geodynamic implications.Due to the newly deployed seismic stations in western and southern South China Sea,we have a better ray path coverage when using the single station method.This is especially true for the coastal region of southern China,where earthquakes occur less frequently and the newly added stations can increase the ray density in this region.We used earthquakes distributed on the periphery of South China Sea and collected earthquake data from 48 stations.We first calculated the group velocity dispersion curves of fundamental mode for Rayleigh waves with periods from 14 s to 130 s using multiple filter technique.Then we conducted subspace inversion to get group velocity distributions for different periods in the region.Finally,on the basis of the relationship between shear wave velocity and group velocity under certain layer structure of the Earth,we obtained the 3D shear wave structures in the form of depth slices and vertical profiles by using a damped least square algorithm.The results show:① High velocities exist in sea basins where velocity image delineates the shape of sea basins:the high velocities in shallow parts may indicate oceanic characteristics of the sea basin crust,while high velocities in deeper parts may come from high velocity materials which remained after the formation of oceanic crust at expanding ocean ridge.The velocity differences among sea basins are consistent with their heat flow values as well as their ages.The high velocities disappear at depths greater than 60 km,and are replaced by a low-velocity zone in a certain depth range.Beneath the low-velocity zone,a NE--SW high-velocity belt is observed at a depth of 200 km,and may be related to the ancient subduction in this region.② Surrounding the South China Sea,there are obvious high velocities representing peripheral subductions.These high-velocity features are segmented and show differences in velocity values,implying nonuniformness of these subducting plates as well as their different subducting angles.③ Above these high-velocities,we see discontinuous low-velocity zones.At shallow depths,these low velocities reflect the thickness of sedimentary layers and the crust,and in mantle depths,the low velocities may correspond to either mantle wedges of the ancient Pacific subduction zones or residual mantle melting anomalies after the cease of South China Sea opening.④ The lithosphere thickness of the South China Sea basin tends to be 60—85 km.
引文
蔡学林,朱介寿.2010.南海复蘑菇状地幔低速柱结构及其地幔动力学[J].中国地质,37(2):268--279.
曹小林,朱介寿,赵连峰,曹家敏,洪学海.2001.南海及邻区地壳上地幔三维S波速度结构的面波波形反演[J].地震学报,23(2):113--124.
房立华.2009.华北地区瑞利面波噪声层析成像研究[D].北京:中国地震局地球物理研究所:50--52.
房立华,吴建平.2009.背景噪声频散曲线测定及其在华北地区的应用[J].地震学报,31(5):544--554.
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.
何正勤,叶太兰,丁志峰.2009.华北东北部的面波相速度层析成像研究[J].地球物理学报,52(5):1233--1242.
黎明碧,金翔龙.2006.中国南海的形成演化及动力学机制研究综述[J].科技通报,22(1):16--20.
李旭,杨牧.2002.加里曼丹及邻区壳体的运动与演化[J].大地构造与成矿学,26(3):235--239.
李永华,吴庆举,张瑞青,潘佳铁,张风雪,曾融生.2009.用面波方法研究上扬子克拉通壳幔速度结构[J].地球物理学报,52(7):1757--1767.
李延兴,张静华,周伟,栾锡武,胡新康,张中伏.2010.南海及周围地区的现今构造活动[J].大地测量与地球动力学,30(3):10--16.
刘昭蜀,赵焕庭,范时清,陈森强.2002.南海地质[M].北京:科学出版社:255--309.
闵慧,任建业,高金耀,左玉山.2010.南海北部古俯冲带的位置及其对南海扩张的控制[J].大地构造与成矿学,34(4):599--605.
彭艳菊,苏伟,郑月军,黄忠贤.2002.中国大陆及海域Love波层析成像[J].地球物理学报,45(6):792--801.
瞿辰,周蕙兰,赵大鹏.2007.使用纵波和横波走时层析成像研究菲律宾海板块西边缘带和南海地区的深部结构[J].地球物理学报,50(6):1757--1768.
夏斌,崔学军,谢建华,王冉.2004.关于南海构造演化动力学机制研究的一点思考[J].大地构造与成矿学,28(3):221--227.
徐果明,李跃,李光品,黄志斌.1994.关于区域性的地震面波层析反演方法的讨论[J].地球物理学进展,9(2):43-53.
徐果明,李光品,王善恩,陈虹,周虎顺.2000.用瑞利面波资料反演中国大陆东部地壳上地幔横波速度的三维结构[J].地球物理学报,43(3):366--376.
杨昊.2007.有限差分法地震波走时计算的快速算法研究[D].长春:吉林大学:24--28.
姚伯初,万玲,吴能友.2004.大南海地区新生代板块构造活动[J].中国地质,31(2):113--122.
姚伯初,万玲,吴能友.2005.南海新生代构造演化及岩石圈三维结构特征[J].地质通报,24(1):1--8.
姚伯初,万玲.2010.南海岩石圈厚度变化特征及其构造意义[J].中国地质,37(4):888--899.
易桂喜,姚华建,朱介寿,Robert D van der Hilst.2008.中国大陆及邻区Rayleigh面波相速度分布特征[J].地球物理学报,51(2):402--411.
张风雪,吴庆举,李永华,张瑞青,潘佳铁.2010.FMM射线追踪方法在地震学正演和反演中的应用[J].地球物理学进展,25(4):1197--1205.
赵会民,吕炳全,孙洪斌,王红罡,徐国强.2002.西太平洋边缘海盆的形成与演化[J].海洋地质与第四纪地质,22(1):57--62.
张健,熊亮萍,汪集旸.2001.南海深部地球动力学特征及其演化机制[J].地球物理学报,44(5):602--610.
朱介寿.1988.地震学中的计算方法[M].北京:地震出版社:474--475.
朱介寿,曹家敏,蔡学林,严忠琼,曹小林.2002.东亚及西太平洋边缘海高分辨率面波层析成像[J].地球物理学报,45(5):646--664.
朱良保,许庆,陈晓非.2002.中国大陆及邻近海域的Rayleigh波群速度分布[J].地球物理学报,45(4):475--482.
Briais A,Patriat P,Tapponnier P.1993.Updated interpretation of magnetic anomalies and seafloor spreading stages inthe South China Sea:Implications for the tertiary tectonics of Southeast Asia[J].J Geophys Res,98(B4):6299-6328.
Herrmann R B,Ammon C J.2004.Computer Programs in Seismology[M/OL].Department of Earth and AtmosphericSciences,St Louis University,St Louis,Missouri.http:∥www.eas.slu.edu/People/RBHerrmann/CPS330.html.
Karig D E.1971.Origin and development of marginal basins in the western Pacific[J].J Geophys Res,76(11):2542-2561.
Lei J S,Zhao D P,Steinberger B,Wu B,Shen F,Li Z.2009.New seismic constraints on the upper mantle structure ofthe Hainan plume[J].Phys Earth Planet Interi,173(1--2):33--50.
Miyashiro A.1986.Hot regions and the origin of marginal basins in the western Pacific[J].Tectonophysics,122(3--4):195--216.
Nakanishi I,Anderson D L.1982.Worldwide distribution of group velocity of mantle Rayleigh waves as determined byspherical harmonic inversion[J].Bull Seism Soc Amer,72(4):1185--1194.
Oldenburg D W,McGillvray P R,Ellis R G.1993.Generalized subspace methods for large-scale inverse problems[J].Geophys J Int,114(1):12--20.
Panza G F.1985.Synthetic seismograms:The Rayleigh waves modal summation[J].J Geophys,58:125--145.
Rawlinson N,Sambridge M.2004.Seismic Traveltime Tomography of the Crust and Lithosphere,Advances in Geophysics[M].Elsevier Academic Press:81--197.
Tapponnier P,Molnar P.1976.Slip-line field theory and large-scale continental tectonics[J].Nature,264(5584):319-324.
Tapponnier P,Peltzer G,Dain A Y L,Armijo R,Cobbold P.1982.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine[J].Geology,10(12):611--616.
Tapponnier P,Peltzer G,Armijo R.1986.On the mechanics of the collision between India and Asia[J].Geological Society,London,Special Publications,19(1):113--157.
Tapponnier P,Lacassin R,Leloup P H,Scharer U,Zhong D L,Wu H W,Liu X H,Ji S C,Zhang L S,Zhong J Y.1990.The Ailao Shan/Red River metamorphic belt:Tertiary left-lateral shear between Indochina and South China[J].Nature,343(6257):431--437.
Taylor B,Hayes D E.1983.Origin and history of the South China Sea basin,in the tectonic and geological evolution ofSoutheast Asian Seas and Islands:Part2[C]∥Hayes D E ed.AGU Geophysical Monograph.Washington D C:23-56.
Wang C,Yang J,Zhu W,Zheng W.1995.Some problems in understanding basin evolution[J].Earth Science Frontiers,2(3):29--44.
Wu H H,Tsai Y B,Lee T Y,Lo C H,Hsieh C H,Toan D V.2004.3-D shear wave velocity structure of the crust andupper mantle in South China Sea and its surrounding regions by surface wave dispersion analysis[J].MarineGeophysical Researches,25(1--2):5--27.
Xu G M.1988.Spherical Radon transform[J].Geophysical Journal,95(2):361--370.
Zheng X F,Jiao W J,Zhang C H,Wang L S.2010.Short-period Rayleigh-wave group velocity tomography throughambient noise cross-correlation in Xinjiang,northwest China[J].Bull Seism Soc Amer,100(3):1350--1355.
曹小林,朱介寿,赵连峰,曹家敏,洪学海.2001.南海及邻区地壳上地幔三维S波速度结构的面波波形反演[J].地震学报,23(2):113--124.
房立华.2009.华北地区瑞利面波噪声层析成像研究[D].北京:中国地震局地球物理研究所:50--52.
房立华,吴建平.2009.背景噪声频散曲线测定及其在华北地区的应用[J].地震学报,31(5):544--554.
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.
何正勤,叶太兰,丁志峰.2009.华北东北部的面波相速度层析成像研究[J].地球物理学报,52(5):1233--1242.
黎明碧,金翔龙.2006.中国南海的形成演化及动力学机制研究综述[J].科技通报,22(1):16--20.
李旭,杨牧.2002.加里曼丹及邻区壳体的运动与演化[J].大地构造与成矿学,26(3):235--239.
李永华,吴庆举,张瑞青,潘佳铁,张风雪,曾融生.2009.用面波方法研究上扬子克拉通壳幔速度结构[J].地球物理学报,52(7):1757--1767.
李延兴,张静华,周伟,栾锡武,胡新康,张中伏.2010.南海及周围地区的现今构造活动[J].大地测量与地球动力学,30(3):10--16.
刘昭蜀,赵焕庭,范时清,陈森强.2002.南海地质[M].北京:科学出版社:255--309.
闵慧,任建业,高金耀,左玉山.2010.南海北部古俯冲带的位置及其对南海扩张的控制[J].大地构造与成矿学,34(4):599--605.
彭艳菊,苏伟,郑月军,黄忠贤.2002.中国大陆及海域Love波层析成像[J].地球物理学报,45(6):792--801.
瞿辰,周蕙兰,赵大鹏.2007.使用纵波和横波走时层析成像研究菲律宾海板块西边缘带和南海地区的深部结构[J].地球物理学报,50(6):1757--1768.
夏斌,崔学军,谢建华,王冉.2004.关于南海构造演化动力学机制研究的一点思考[J].大地构造与成矿学,28(3):221--227.
徐果明,李跃,李光品,黄志斌.1994.关于区域性的地震面波层析反演方法的讨论[J].地球物理学进展,9(2):43-53.
徐果明,李光品,王善恩,陈虹,周虎顺.2000.用瑞利面波资料反演中国大陆东部地壳上地幔横波速度的三维结构[J].地球物理学报,43(3):366--376.
杨昊.2007.有限差分法地震波走时计算的快速算法研究[D].长春:吉林大学:24--28.
姚伯初,万玲,吴能友.2004.大南海地区新生代板块构造活动[J].中国地质,31(2):113--122.
姚伯初,万玲,吴能友.2005.南海新生代构造演化及岩石圈三维结构特征[J].地质通报,24(1):1--8.
姚伯初,万玲.2010.南海岩石圈厚度变化特征及其构造意义[J].中国地质,37(4):888--899.
易桂喜,姚华建,朱介寿,Robert D van der Hilst.2008.中国大陆及邻区Rayleigh面波相速度分布特征[J].地球物理学报,51(2):402--411.
张风雪,吴庆举,李永华,张瑞青,潘佳铁.2010.FMM射线追踪方法在地震学正演和反演中的应用[J].地球物理学进展,25(4):1197--1205.
赵会民,吕炳全,孙洪斌,王红罡,徐国强.2002.西太平洋边缘海盆的形成与演化[J].海洋地质与第四纪地质,22(1):57--62.
张健,熊亮萍,汪集旸.2001.南海深部地球动力学特征及其演化机制[J].地球物理学报,44(5):602--610.
朱介寿.1988.地震学中的计算方法[M].北京:地震出版社:474--475.
朱介寿,曹家敏,蔡学林,严忠琼,曹小林.2002.东亚及西太平洋边缘海高分辨率面波层析成像[J].地球物理学报,45(5):646--664.
朱良保,许庆,陈晓非.2002.中国大陆及邻近海域的Rayleigh波群速度分布[J].地球物理学报,45(4):475--482.
Briais A,Patriat P,Tapponnier P.1993.Updated interpretation of magnetic anomalies and seafloor spreading stages inthe South China Sea:Implications for the tertiary tectonics of Southeast Asia[J].J Geophys Res,98(B4):6299-6328.
Herrmann R B,Ammon C J.2004.Computer Programs in Seismology[M/OL].Department of Earth and AtmosphericSciences,St Louis University,St Louis,Missouri.http:∥www.eas.slu.edu/People/RBHerrmann/CPS330.html.
Karig D E.1971.Origin and development of marginal basins in the western Pacific[J].J Geophys Res,76(11):2542-2561.
Lei J S,Zhao D P,Steinberger B,Wu B,Shen F,Li Z.2009.New seismic constraints on the upper mantle structure ofthe Hainan plume[J].Phys Earth Planet Interi,173(1--2):33--50.
Miyashiro A.1986.Hot regions and the origin of marginal basins in the western Pacific[J].Tectonophysics,122(3--4):195--216.
Nakanishi I,Anderson D L.1982.Worldwide distribution of group velocity of mantle Rayleigh waves as determined byspherical harmonic inversion[J].Bull Seism Soc Amer,72(4):1185--1194.
Oldenburg D W,McGillvray P R,Ellis R G.1993.Generalized subspace methods for large-scale inverse problems[J].Geophys J Int,114(1):12--20.
Panza G F.1985.Synthetic seismograms:The Rayleigh waves modal summation[J].J Geophys,58:125--145.
Rawlinson N,Sambridge M.2004.Seismic Traveltime Tomography of the Crust and Lithosphere,Advances in Geophysics[M].Elsevier Academic Press:81--197.
Tapponnier P,Molnar P.1976.Slip-line field theory and large-scale continental tectonics[J].Nature,264(5584):319-324.
Tapponnier P,Peltzer G,Dain A Y L,Armijo R,Cobbold P.1982.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine[J].Geology,10(12):611--616.
Tapponnier P,Peltzer G,Armijo R.1986.On the mechanics of the collision between India and Asia[J].Geological Society,London,Special Publications,19(1):113--157.
Tapponnier P,Lacassin R,Leloup P H,Scharer U,Zhong D L,Wu H W,Liu X H,Ji S C,Zhang L S,Zhong J Y.1990.The Ailao Shan/Red River metamorphic belt:Tertiary left-lateral shear between Indochina and South China[J].Nature,343(6257):431--437.
Taylor B,Hayes D E.1983.Origin and history of the South China Sea basin,in the tectonic and geological evolution ofSoutheast Asian Seas and Islands:Part2[C]∥Hayes D E ed.AGU Geophysical Monograph.Washington D C:23-56.
Wang C,Yang J,Zhu W,Zheng W.1995.Some problems in understanding basin evolution[J].Earth Science Frontiers,2(3):29--44.
Wu H H,Tsai Y B,Lee T Y,Lo C H,Hsieh C H,Toan D V.2004.3-D shear wave velocity structure of the crust andupper mantle in South China Sea and its surrounding regions by surface wave dispersion analysis[J].MarineGeophysical Researches,25(1--2):5--27.
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