青藏高原东缘上地幔顶部Pn波速度结构及各向异性研究
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摘要
本研究使用中国地震局地壳应力研究所2010—2011年期间在云南地区布设流动地震台站以及青藏高原周边地区固定地震台站记录到的波形资料,提取了大量高质量Pn波到时资料.联合中国地震台网观测报告,我们获得了一个新的青藏高原东缘上地幔顶部Pn波速度和各向异性结构模型.结果显示,研究区内上地幔顶部存在明显横向不均匀性.古老盆地和稳定地台区如四川盆地、柴达木盆地、拉萨地块和阿拉善块体呈现为明显高波速异常,而祁连山至西秦岭褶皱带和川滇菱形块体北部等为相对弱高波速异常.在龙日坝断裂带以东的松潘—甘孜地块往南沿安宁河—则木河断裂至川滇菱形块体南部显示为一条近南北向明显低波速异常.三江褶皱系、缅甸弧俯冲带以及四川盆地东南等地区为明显低波速异常.地壳强震多发生在高波速异常边缘或高低波速异常过渡带上,表明地壳强震的孕育可能还与地幔构造作用存在一定相关性.青藏高原东构造结的各向异性快波方向呈顺时针旋转分布,与印度—欧亚碰撞密切相关.龙门山断裂带东西两侧的各向异性快波方向发生明显变化,由其西侧松潘—甘孜地块下方的NE向转变为四川盆地下方的近EW向,说明青藏高原物质流动遇四川盆地后分为NE和SW向两支.在川滇地区26°N以南地区上地幔顶部各向异性呈现近NS向与地表GPS观测相一致,但与SKS分裂结果存在较大差异,可能表明地壳与上地幔顶部形变表现为耦合现象,而上地幔顶部至岩石圈内部则存在解耦现象.
In the present study a large number of high-quality Pn arrival times were hand-picked from seismograms recorded by the portable seismic stations,deployed from 2010 to 2011 in the Yunnan region by the Institute of Crustal Dynamics,CEA and recorded by Chinese permanent seismic stations around the eastern Tibetan plateau.Combining with the data from the observational bulletins of Chinese provincial seismic networks,we obtained a new model of seismic velocity and anisotropy of the uppermost mantle under the eastern Tibetan plateau.Our results show obvious lateral heterogeneities in the study region.The old basins and stable blocks,such as the Sichuan and Qaidam basins and Lhasa and Alashan blocks,show prominent high-velocity anomalies,while the Qilian-Qinling fold zone and northern Chuan-Dian diamond-shaped block exhibit relatively weaker high-velocity anomalies.A pronounced north-south trending low-velocity anomaly zone exists from the Songpan-Garzê block east of the Longriba fault,southward through the Anning-Zemu fault zone to the southern Chuan-Dian diamond-shaped block.In the Sanjiang fold system,Burma-subduction zone and the region southeast of the Sichuan basin,there are three obvious low-velocity anomalies.Most of crustal major earthquakes occur on the edges of high-velocity anomalies or the transition zone from high to low velocities,suggesting that crustal earthquakes may be somewhat related to the mantle structure.The fast direction of Pn propagation around the eastern Himalayan syntaxis rotates in a clockwise manner,suggesting that it is related to the Indo-Asian collision.The fast direction changes sharply across the Longmenshan fault zone from NE under the Songpan-Garzê block in the west to EW under the Sichuan basin in the east,implying that the material flow of the Tibetan plateau is divided into the NE and SW braches when it meets the Sichuan basin.To south of 26°N,in the Chuan-Dian region the Pn fast direction is in an approximate N-S direction,which is consistent with the GPS observations but different from SKS splitting results,suggesting the mechanically coupling of the crust and the uppermost mantle but decoupling at certain depths between the uppermost and lithospheric mantle.
In the present study a large number of high-quality Pn arrival times were hand-picked from seismograms recorded by the portable seismic stations,deployed from 2010 to 2011 in the Yunnan region by the Institute of Crustal Dynamics,CEA and recorded by Chinese permanent seismic stations around the eastern Tibetan plateau.Combining with the data from the observational bulletins of Chinese provincial seismic networks,we obtained a new model of seismic velocity and anisotropy of the uppermost mantle under the eastern Tibetan plateau.Our results show obvious lateral heterogeneities in the study region.The old basins and stable blocks,such as the Sichuan and Qaidam basins and Lhasa and Alashan blocks,show prominent high-velocity anomalies,while the Qilian-Qinling fold zone and northern Chuan-Dian diamond-shaped block exhibit relatively weaker high-velocity anomalies.A pronounced north-south trending low-velocity anomaly zone exists from the Songpan-Garzê block east of the Longriba fault,southward through the Anning-Zemu fault zone to the southern Chuan-Dian diamond-shaped block.In the Sanjiang fold system,Burma-subduction zone and the region southeast of the Sichuan basin,there are three obvious low-velocity anomalies.Most of crustal major earthquakes occur on the edges of high-velocity anomalies or the transition zone from high to low velocities,suggesting that crustal earthquakes may be somewhat related to the mantle structure.The fast direction of Pn propagation around the eastern Himalayan syntaxis rotates in a clockwise manner,suggesting that it is related to the Indo-Asian collision.The fast direction changes sharply across the Longmenshan fault zone from NE under the Songpan-Garzê block in the west to EW under the Sichuan basin in the east,implying that the material flow of the Tibetan plateau is divided into the NE and SW braches when it meets the Sichuan basin.To south of 26°N,in the Chuan-Dian region the Pn fast direction is in an approximate N-S direction,which is consistent with the GPS observations but different from SKS splitting results,suggesting the mechanically coupling of the crust and the uppermost mantle but decoupling at certain depths between the uppermost and lithospheric mantle.
引文
[1]阚荣举,林中洋.云南地壳上地幔构造的初步研究.中国地震,1986,2(4):50-61.Kan R J,Lin Z Y.A preliminary study on crustal and uppermantle structures in Yunnan.Earthquake Research in China(in Chinese),1986,2(4):50-61.
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[6]Lei J,Zhao D.Structural heterogeneity of the Longmenshanfault zone and the mechanism of the 2008 Wenchuanearthquake(Ms8.0).Geochemistry Geophysics Geosystems,2009,10(10):Q10010,doi:10.1029/2009GC002590.
[7]王椿镛,常利军,吕智勇等.青藏高原东部上地幔各向异性及相关的壳幔耦合型式.中国科学(D辑),2007,37(4):495-503.Wang C Y,Chang L J,LüZ Y,et al.Seismic anisotropy ofupper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern.Science in China(Series D)(inChinese),2007,37(4):495-503.
[8]Wang C Y,Flesch L M,Flesch L M,et al.Evidence formechanically coupled lithosphere in central Asia and resultingimplications.Geology,2008,36(5):363-365.
[9]常利军,王椿镛,丁志峰.四川及邻区上地幔各向异性研究.中国科学(D辑),2008,38(12):1589-1599.Chang L J,Wang C Y,Ding Z F.Study on seismicanisotropy of upper mantle beneath the Sichuan and itsadjacent areas.Sci.China(Series D),2008,38(12):1589-1599.
[10]Li J,Wang X J,Niu F L.Seismic anisotropy andimplications for mantle deformation beneath the NE margin ofthe Tibet plateau and Ordos plateau.Phys.Earth Planet.Inter.,2011,189(3-4):157-170.
[11]李永华,吴庆举,田小波等.用接收函数方法研究云南及其邻区地壳上地幔结构.地球物理学报,2009,52(1):67-80.Li Y H,Wu Q J,Tian X B,et al.Crustal structure in theYunnan region determined by modeling receiver functions.Chinese J.Geophys.(in Chinese),2009,52(1):67-80.
[12]Zhang Z J,Yuan X H,Chen Y,et al.Seismic signature ofthe collision between the east Tibetan escape flow and theSichuan Basin.Earth Planet.Sci.Lett.,2010,292(3-4):254-264.
[13]Hu J F,Xu X Q,Yang H Y,et al.S receiver functionanalysis of the crustal and lithospheric structures beneatheastern Tibet.Earth Planet.Sci.Lett.,2011,306(1-2):77-85.
[14]Wang Q,Zhang P Z,Freymueller J T,et al.Present-daycrustal deformation in China constrained by global positioningsystem measurements.Science,2001,294(5542):574-577.
[15]Zhang P Z,Shen Z K,Wang M,et al.Continuousdeformation of the Tibetan plateau from global positioningsystem data.Geology,2004,32(9):809-812.
[16]Gan W J,Zhang P Z,Shen Z K,et al.Present-day crustalmotion within the Tibetan Plateau inferred from GPSmeasurements.J.Geophys.Res.,2007,112:B08416,doi:10.1029/2005JB004120.
[17]Hearn T M,Wang S Y,Ni J F,et al.Uppermost mantlevelocities beneath China and surrounding regions.J.Geophys.Res.,2004,109:B11301,doi:10.1029/2003JB002874.
[18]Liang C T,Song X D,Huang J L.Tomographic inversion ofPn travel times in China.J.Geophys.Res.,2004,109:B11304,doi:10.1029/2003JB002789.
[19]Pei S P,Zhao J M,Sun Y M,et al.Upper mantle seismicvelocities and anisotropy in China determined through Pn andSn tomography.J.Geophys.Res.,2007,112:B05312,doi:10.1029/2006JB004409.
[20]McNamara D E,Walter W R,Owens T J,et al.Uppermantle velocity structure beneath the Tibetan Plateau fromPn travel time tomography.J.Geophys.Res.,1997,102(B1):493-505.
[21]黄金莉,宋晓东,汪素云.川滇地区上地幔顶部Pn速度细结构.中国科学(D辑:地球科学),2003,33(增刊):144-150.Huang J L,Song X D,Wang S Y.Fine structure of Pnvelocity beneath Sichuan-Yunnan region.Science in China(Series D)(in Chinese),2003,33(Suppl.):144-150.
[22]Liang C T,Song X D.A low velocity belt beneath northernand eastern Tibetan Plateau from Pn tomography.Geophys.Res.Lett.,2006,33:L22306,doi:10.1029/2006gl027926.
[23]崔忠雄,裴顺平.青藏高原东构造结及周边地区上地幔顶部Pn速度结构和各向异性研究.地球物理学报,2009,52(9):2245-2254.Cui Z X,Pei S P.Study on Pn velocity and anisotropy in theuppermost mantle of the Eastern Himalayan Syntaxis andsurrounding regions.Chinese J.Geophys.(in Chinese),2009,52(9):2245-2254.
[24]胥颐,李志伟,黄润秋等.四川西部暨龙门山地区的Pn波速度和各向异性.中国科学(地球科学),2010,40(4):452-457.Xu Y,Li Z W,Huang R Q,et al.Pn-wave velocity andanisotropy of the western Sichuan and Longmen Mountainregion,China.Sci.China Earth Sci.(in Chinese),2010,40(4):452-457.
[25]李飞,周仕勇,苏有锦等.川滇及邻区Pn波速度结构和各向异性研究.地球物理学报,2011,54(1):44-54.Li F,Zhou S Y,Su Y J,et al.Study on Pn-wave velocitystructure and anisotropy in the Sichuan-Yunnan and itsadjacent.Chinese J.Geophys.(in Chinese),54(1):44-54.
[26]Lei J S,Zhang G W,Xie F R,et al.Relocation of the 10March 2011Yingjiang,China,earthquake sequence and itstectonic implications.Earthquake Science,2012,25(1):103-110.
[27]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.地球物理学报,2009,52(5):1412-1417.Zheng X F,Ouyang B,Zhang D N,et al.Technical systemconstruction of Data Backup Centre for China SeismographNetwork and the data support to researches on the Wenchuanearthquake.Chinese J.Geophys.(in Chinese),2009,52(5):1412-1417.
[28]Hearn T M.Anisotropic Pn tomography in the westernUnited States.J.Geophys.Res.,1996,101(B4):8403-8414.
[29]Boschi L.Global multiresolution models of surface wavepropagation:comparing equivalently regularized Born and raytheoretical solutions.Geophys.J.Int.,2006,167(1):238-252.
[30]Lei J S,Zhao D P,Steinberger B,et al.New seismicconstraints on the upper mantle structure of the Hainanplume.Phys.Earth Planet.Inter.,2009,173(1-2):33-50.
[31]Lei J S,Xie F R,Mishra O P,et al.The 2011Yingjiang,China,earthquake:A volcano-related fluid-driven earthquake?Bull.Seismol.Soc.Am.,2012,102(1):417-425.
[32]Tian X B,Zhang Z L,Si S K,et al.SKS splittingmeasurements with horizontal component misalignment.Geophys.J.Int.,2011,185(1):329-340.
[33]黄忠贤.华北地区地壳上地幔速度各向异性研究.地球物理学报,2011,54(3):681-691.Huang Z X.Velocity anisotropy in the crust and uppermantle of North China.Chinese J.Geophys.(in Chinese),2011,54(3):681-691.
[34]Hearn T M.Uppermost mantle velocities and anisotropybeneath Europe.J.Geophys.Res.,1999,104(B7):15123-15139.
[35]Bassin C,Laske G,Masters G.The current limits ofresolution for surface wave tomography in North America.EOS Trans.AGU,2000,81:F897.
[36]Lei J S.Seismic tomographic imaging of the crust and uppermantle under the central and western Tien Shan orogenicbelt.J.Geophys.Res.,2011,116:B09305,doi:10.1029/2010JB008000.
[37]许忠淮,汪素云,裴顺平.青藏高原东北缘地区Pn波速度的横向变化.地震学报,2003,25(1):24-31.Xu Z H,Wang S Y,Pei S P.Lateral variation of Pn velocitybeneath northeastern marginal region of Qingzang plateau.Acta Seismol.Sinica(in Chinese),2003,25(1):24-31.
[38]Royden L,Burchfiel B,Rovert W,et al.Surfacedeformation and lower crustal flow in eastern Tibet.Science,1997,276(5313):788-790.
[2]滕吉文.康滇构造带岩石圈物理与动力学.北京:科学出版社,1994.Teng J W.Physics and Dynamics of the Lithosphere in Kang-Dian Tectonic Belt(in Chinese).Beijing:Sciences Press,1994.
[3]Zhang Z J,Bai Z M,Wang C Y,et al.The crustal structureunder Sanjiang and its dynamic implications:revealed byseismic reflection/refraction profile between Zhefang andBinchuan,Yunnan.Science in China(Series D),2005,48(9):1329-1336.
[4]Wang C Y,Chan W W,Mooney W D.Three-dimensionalvelocity structure of crust and upper mantle in southwesternChina and its tectonic implications.J.Geophys.Res.,2003,108,B92442,doi:10.1029/2002JB001973.
[5]Lei J S,Zhao D P,Su Y J.Insight into the origin of theTengchong intraplate volcano and seismotectonics in southwestChina from local and teleseismic data.J.Geophys.Res.,2009,114:B05302,doi:10.1029/2008JB005881.
[6]Lei J,Zhao D.Structural heterogeneity of the Longmenshanfault zone and the mechanism of the 2008 Wenchuanearthquake(Ms8.0).Geochemistry Geophysics Geosystems,2009,10(10):Q10010,doi:10.1029/2009GC002590.
[7]王椿镛,常利军,吕智勇等.青藏高原东部上地幔各向异性及相关的壳幔耦合型式.中国科学(D辑),2007,37(4):495-503.Wang C Y,Chang L J,LüZ Y,et al.Seismic anisotropy ofupper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern.Science in China(Series D)(inChinese),2007,37(4):495-503.
[8]Wang C Y,Flesch L M,Flesch L M,et al.Evidence formechanically coupled lithosphere in central Asia and resultingimplications.Geology,2008,36(5):363-365.
[9]常利军,王椿镛,丁志峰.四川及邻区上地幔各向异性研究.中国科学(D辑),2008,38(12):1589-1599.Chang L J,Wang C Y,Ding Z F.Study on seismicanisotropy of upper mantle beneath the Sichuan and itsadjacent areas.Sci.China(Series D),2008,38(12):1589-1599.
[10]Li J,Wang X J,Niu F L.Seismic anisotropy andimplications for mantle deformation beneath the NE margin ofthe Tibet plateau and Ordos plateau.Phys.Earth Planet.Inter.,2011,189(3-4):157-170.
[11]李永华,吴庆举,田小波等.用接收函数方法研究云南及其邻区地壳上地幔结构.地球物理学报,2009,52(1):67-80.Li Y H,Wu Q J,Tian X B,et al.Crustal structure in theYunnan region determined by modeling receiver functions.Chinese J.Geophys.(in Chinese),2009,52(1):67-80.
[12]Zhang Z J,Yuan X H,Chen Y,et al.Seismic signature ofthe collision between the east Tibetan escape flow and theSichuan Basin.Earth Planet.Sci.Lett.,2010,292(3-4):254-264.
[13]Hu J F,Xu X Q,Yang H Y,et al.S receiver functionanalysis of the crustal and lithospheric structures beneatheastern Tibet.Earth Planet.Sci.Lett.,2011,306(1-2):77-85.
[14]Wang Q,Zhang P Z,Freymueller J T,et al.Present-daycrustal deformation in China constrained by global positioningsystem measurements.Science,2001,294(5542):574-577.
[15]Zhang P Z,Shen Z K,Wang M,et al.Continuousdeformation of the Tibetan plateau from global positioningsystem data.Geology,2004,32(9):809-812.
[16]Gan W J,Zhang P Z,Shen Z K,et al.Present-day crustalmotion within the Tibetan Plateau inferred from GPSmeasurements.J.Geophys.Res.,2007,112:B08416,doi:10.1029/2005JB004120.
[17]Hearn T M,Wang S Y,Ni J F,et al.Uppermost mantlevelocities beneath China and surrounding regions.J.Geophys.Res.,2004,109:B11301,doi:10.1029/2003JB002874.
[18]Liang C T,Song X D,Huang J L.Tomographic inversion ofPn travel times in China.J.Geophys.Res.,2004,109:B11304,doi:10.1029/2003JB002789.
[19]Pei S P,Zhao J M,Sun Y M,et al.Upper mantle seismicvelocities and anisotropy in China determined through Pn andSn tomography.J.Geophys.Res.,2007,112:B05312,doi:10.1029/2006JB004409.
[20]McNamara D E,Walter W R,Owens T J,et al.Uppermantle velocity structure beneath the Tibetan Plateau fromPn travel time tomography.J.Geophys.Res.,1997,102(B1):493-505.
[21]黄金莉,宋晓东,汪素云.川滇地区上地幔顶部Pn速度细结构.中国科学(D辑:地球科学),2003,33(增刊):144-150.Huang J L,Song X D,Wang S Y.Fine structure of Pnvelocity beneath Sichuan-Yunnan region.Science in China(Series D)(in Chinese),2003,33(Suppl.):144-150.
[22]Liang C T,Song X D.A low velocity belt beneath northernand eastern Tibetan Plateau from Pn tomography.Geophys.Res.Lett.,2006,33:L22306,doi:10.1029/2006gl027926.
[23]崔忠雄,裴顺平.青藏高原东构造结及周边地区上地幔顶部Pn速度结构和各向异性研究.地球物理学报,2009,52(9):2245-2254.Cui Z X,Pei S P.Study on Pn velocity and anisotropy in theuppermost mantle of the Eastern Himalayan Syntaxis andsurrounding regions.Chinese J.Geophys.(in Chinese),2009,52(9):2245-2254.
[24]胥颐,李志伟,黄润秋等.四川西部暨龙门山地区的Pn波速度和各向异性.中国科学(地球科学),2010,40(4):452-457.Xu Y,Li Z W,Huang R Q,et al.Pn-wave velocity andanisotropy of the western Sichuan and Longmen Mountainregion,China.Sci.China Earth Sci.(in Chinese),2010,40(4):452-457.
[25]李飞,周仕勇,苏有锦等.川滇及邻区Pn波速度结构和各向异性研究.地球物理学报,2011,54(1):44-54.Li F,Zhou S Y,Su Y J,et al.Study on Pn-wave velocitystructure and anisotropy in the Sichuan-Yunnan and itsadjacent.Chinese J.Geophys.(in Chinese),54(1):44-54.
[26]Lei J S,Zhang G W,Xie F R,et al.Relocation of the 10March 2011Yingjiang,China,earthquake sequence and itstectonic implications.Earthquake Science,2012,25(1):103-110.
[27]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.地球物理学报,2009,52(5):1412-1417.Zheng X F,Ouyang B,Zhang D N,et al.Technical systemconstruction of Data Backup Centre for China SeismographNetwork and the data support to researches on the Wenchuanearthquake.Chinese J.Geophys.(in Chinese),2009,52(5):1412-1417.
[28]Hearn T M.Anisotropic Pn tomography in the westernUnited States.J.Geophys.Res.,1996,101(B4):8403-8414.
[29]Boschi L.Global multiresolution models of surface wavepropagation:comparing equivalently regularized Born and raytheoretical solutions.Geophys.J.Int.,2006,167(1):238-252.
[30]Lei J S,Zhao D P,Steinberger B,et al.New seismicconstraints on the upper mantle structure of the Hainanplume.Phys.Earth Planet.Inter.,2009,173(1-2):33-50.
[31]Lei J S,Xie F R,Mishra O P,et al.The 2011Yingjiang,China,earthquake:A volcano-related fluid-driven earthquake?Bull.Seismol.Soc.Am.,2012,102(1):417-425.
[32]Tian X B,Zhang Z L,Si S K,et al.SKS splittingmeasurements with horizontal component misalignment.Geophys.J.Int.,2011,185(1):329-340.
[33]黄忠贤.华北地区地壳上地幔速度各向异性研究.地球物理学报,2011,54(3):681-691.Huang Z X.Velocity anisotropy in the crust and uppermantle of North China.Chinese J.Geophys.(in Chinese),2011,54(3):681-691.
[34]Hearn T M.Uppermost mantle velocities and anisotropybeneath Europe.J.Geophys.Res.,1999,104(B7):15123-15139.
[35]Bassin C,Laske G,Masters G.The current limits ofresolution for surface wave tomography in North America.EOS Trans.AGU,2000,81:F897.
[36]Lei J S.Seismic tomographic imaging of the crust and uppermantle under the central and western Tien Shan orogenicbelt.J.Geophys.Res.,2011,116:B09305,doi:10.1029/2010JB008000.
[37]许忠淮,汪素云,裴顺平.青藏高原东北缘地区Pn波速度的横向变化.地震学报,2003,25(1):24-31.Xu Z H,Wang S Y,Pei S P.Lateral variation of Pn velocitybeneath northeastern marginal region of Qingzang plateau.Acta Seismol.Sinica(in Chinese),2003,25(1):24-31.
[38]Royden L,Burchfiel B,Rovert W,et al.Surfacedeformation and lower crustal flow in eastern Tibet.Science,1997,276(5313):788-790.
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