中天山及邻区S波分裂研究及其动力学意义
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摘要
本文利用天山及其邻区布设的37个宽频带地震台站记录到的远震波形数据,分别采用最小能量法和旋转相关法对SKS和SKKS波震相进行了偏振分析,计算出了台站下方介质的S波分裂参数:快波的偏振方向(φ)和慢波延迟时间(δt).本文研究结果表明:中天山内部大多数台站的各向异性快波方向呈NEE-SWW向,与天山走向平行,慢波时间延迟为0.4～1.7 s,这是塔里木、哈萨克斯坦的南北双向俯冲及其导致的天山地区岩石圈地幔南北向缩短变形的直接反映.本文研究发现中天山北部部分台站下方地震各向异性快波方向与慢波延时随方位角呈现规律性的变化,可能暗示该区上地幔各向异性不能仅用单层水平各向异性这一简单模式来解释.75°E以西的天山地区台站下方S波快波方向和延时具有强烈的横向变化,可能与研究区下方存在的小规模对流有关.中天山不同地段地震台站下方各向异性明显不同,进一步证实了天山地区构造变形的复杂性.
Seismic anisotropy beneath the Central Tien Shan is investigated using shear-wave splitting of SKS and SKKS phases.We analyzed teleseismic events recorded by 37 broadband stations in the Central Tien Shan and its vicinity.Fast polarization directions (φ) and delay times (δt) are determined with both the minimum energy method and rotation-correlation method.Our results suggest that the fast polarization direction of most stations in this area is NEE-SWW, parallel to the strike of the Tien Shan,the delay time is about 0.4～1.7 s.All of these are exactly the direct reflection of the NS shortening deformation of the lithosphere mantle beneath this area,which is related to the double subduction of Tarim and Kazakhstan.At some stations in the northern part of Central Tien Shan the splitting parameters vary with event back azimuth regularly,which implies that the actual upper-mantle structure is more complex than a single anisotropic layer with horizontal fast axis.The strong transverse variety of the shear wave fast polarizations and delay times of the stations in the west of 75°E maybe related to the small-scale convection beneath this region.The obvious differences of anisotropy between different parts of the Tien Shan verify the complexity of the lithosphere deformation beneath this region.
Seismic anisotropy beneath the Central Tien Shan is investigated using shear-wave splitting of SKS and SKKS phases.We analyzed teleseismic events recorded by 37 broadband stations in the Central Tien Shan and its vicinity.Fast polarization directions (φ) and delay times (δt) are determined with both the minimum energy method and rotation-correlation method.Our results suggest that the fast polarization direction of most stations in this area is NEE-SWW, parallel to the strike of the Tien Shan,the delay time is about 0.4～1.7 s.All of these are exactly the direct reflection of the NS shortening deformation of the lithosphere mantle beneath this area,which is related to the double subduction of Tarim and Kazakhstan.At some stations in the northern part of Central Tien Shan the splitting parameters vary with event back azimuth regularly,which implies that the actual upper-mantle structure is more complex than a single anisotropic layer with horizontal fast axis.The strong transverse variety of the shear wave fast polarizations and delay times of the stations in the west of 75°E maybe related to the small-scale convection beneath this region.The obvious differences of anisotropy between different parts of the Tien Shan verify the complexity of the lithosphere deformation beneath this region.
引文
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[15] Li A,Chen C.Shear wave splitting beneath the central Tien Shan and tectonic implications.Geophys.Res.Lett.,2006,33,L22303,doi:10． 1029/2006GL027717
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[18] 杨少敏.李杰,王琪.GPS研究天山现今变形与断层活动.中国科学(D辑),2008,38(7) :872～880 Yang S M,Li J,Wang Q.The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations.Science in China (Series D) (in Chinese),2008,38(7) :872～880
[19] 郑斯华,高原.中国大陆岩石层的方位各向异性.地震学报,1994,16(2) :131～140 Zheng S H,Gao Y.The azimuthal anisotropy of rock layer in China mainland.Acta Seismologica Sinica (in Chinese),1994,16(2) :131～140
[20] 罗艳,黄忠贤,彭艳菊等.中国大陆及邻区SKS波分裂研究.地球物理学报,2004,47(5) :812～821 LuoY,HuangZX,Peng Y J,et al.A study on SKSwave splitting beneath the China mainland and adjacent regions.Chinese J.Geophys.(in Chinese),2004,47(5) :812～821
[21] 高原,滕吉文.中国大陆地壳与上地幔地震各向异性研究.地球物理学进展,2005,20(1) :180～185 Gao Y,Teng J W.Studies on seismic anisotropy in the crust and mantle on Chinese mainland.Progress in Geophysics (in Chinese),2005,20(1) :180～185
[22] Barruol G,Hoffmann R.Seismic anisotropy beneath the Geoscope stations from SKS splitting.J.Geophys.Res.,1999,104(B5) :10757～10774
[23] Chen Y P,Wang L S,Mi N,et al.Shear wave splitting observations in the Chinese Tianshan orogenic belt.Geophys.Res.Lett.,2005,32,L07306,doi:10． 1029/2004GL021686
[24] Vinnik L P,Aleshin I M,Kiselev S G.Depth localized azimuthal anisotropy from SKS and P receiver functions:The TienShan.Geophys.J.Int.,2007,169(3) :1289～1299
[25] Roecker S W.Constraints on the crust and upper mantle of the Kyrgyz Tien Shan from the preliminary analysis of CHENGIS broadband data.Russ.Geol.Geophys.,2001,42:1554～1565
[26] Li Y H,Wu Q J,Jiang L J,et al.Complex seismic anisotropic structure beneath the central Tien Shan revealed by shear wave splitting.Geophys.J.Int.,2010,181 (3) :1678～1686
[27] Gao S S,Liu K H.Significant seismic anisotropy beneath the southern Lhasa Terrane,Tibetan Plateau.Geochem.Geophys.Geosyst.,2009,10,Q02008,doi:10． 1029/2008GC002227
[28] W(u|¨)stefeld A,Bokelmann G H R.Null detection in shearwave splitting measurements.Bull.Seismol.Soc.Am.,2007,97(4) :1204～1211
[29] W(u|¨)stefeld A,Bokelmann G H R,Zaroli C,et al.SplitLab:a shear-wave splitting environment in Matlab.Comput.Geosci.,2008,34(5) :515～528
[30] Bowman J R,Ando M.Shear-wave splitting in the uppermantle wedge above the Tonga subduction zone.Geophys.J.R.Astron.Soc.,1987,88:25～41
[31] Silver P G,Chan W W.Shear wave splitting and subcontinental mantle deformation.J.Geophys.Res.,1991,96:16429～16454
[32] Vecsey L,Plomerova J,Babuska V.Shear-wave splitting measurements-Problems and solutions.Tectonophysics,2008,462:178～196
[33] Silver P G.Seismic anisotropy beneath the continents:probing the depth of geology.Annu.Rev.Earth Planet.Sci.,1996,24:385～432
[34] Levin V,Menke W,Park J.Shear-wave splitting in Appalachians:a case for multilayered anisotropy.J.Geophys.Res.,1999,104:17975～17994
[2] 高锐,肖序常,高弘等.西昆仑-塔里木-天山岩石圈深地震探测综述.地质通报,2002,21(1) :11～18 Gao R,Xiao X C,Gao H,et al.Summary of deep seismic probing of the lithospheric structure across the West Kunlun-Tarim-Tianshan.Geological Bulletin of China (in Chinese),2002,21(1) :11～18
[3] 赵俊猛.天山造山带与准噶尔盆地岩石圈结构及其动力学过程[博士论文].北京:中国地震局地质研究所,2004 Zhao J M.The lithosphere structure and dynamic processes in Tianshan orogenic belt and Junggar Basin[Ph.D.thesis](in Chinese).Beijing:Institute of Geology,China Earthquake Administration,2004
[4] Zhao J,Liu G,Lu Z,et al.Lithospheric structure and dynamic processes of the Tianshan orogenic belt and the Junggar basin.Tectonophysics,2003,376:199～239
[5] Vinnik L P,Saipekova A M.Structure of the lithosphere and asthenosphere of the Tien Shan.Ann.Geophys.,1984,2 (6) :621～626
[6] Roecker S W,Sabitova T M,Vinnik L P,et al.3-dimensional elastic wave velocity structure of the western and central Tian Shan.J.Geophys.Res.,1993,98(B9) :15779～15795
[7] Lei J S,Zhao D P.Teleseismic P-wave tomography and the upper mantle structure of the central Tien Shan orogenic belt.Physics of the Earth and Planetary Interiors,2007,162(3-4) :165～185
[8] 胥颐,刘福田,刘建华等.中国大陆西北造山带及其毗邻盆地的地震层析成像.中国科学(D辑),2000,30(2) :113～122 Xu Y,Liu F T,Liu J H,et al.The seismic tomography of Northwest China orogenic belt and its adjacent basin.Science in China (SeriesD) (in Chinese),2000,30(2) :113～122
[9] 郭飚,刘启元,陈九辉等.中国境内天山地壳上地幔结构的地震层析成像.地球物理学报,2006,49(6) :1693～1700 Guo B,Liu Q Y,Chen J H,et al.Seismic tomography of the crust and upper mantle structure underneath the Chinese Tienshan.Chinese J.Geophys.(in Chinese),2006,49(6) :1693～1700
[10] Chen Y H,Roecker S W,Kosarev G L.Elevation of the 410 km discontinuity beneath the central Tien Shan:evidence for a detached lithospheric root.Geophys.Res.Lett.,1997,24:1531～1534
[11] Vinnik L P,Reigber C,Aleshin I M.Receiver function tomography of the central Tien Shan.Earth and Planetary Science Letters,2004,225(1～2) :131～146
[12] Tian X B,Zhao D P,Zhang H S,et al.Mantle transition zone topography and structure beneath the central Tien Shan orogenic belt.J.Geophys.Res.,2010,2008JB006229 (Accepted)
[13] Makeyeva L I,Vinnik L P,Roecker S W.Shear-wave splitting and small-scale convection in the continental upper mantle.Nature,1992,358:144～147
[14] Wolfe C J,Vernon F.Shear wave splitting at central Tian Shan:evidence for rapid variation of anisotropic patterns.Geophys.Res.Lett.,1998,25(8) :1217～1220
[15] Li A,Chen C.Shear wave splitting beneath the central Tien Shan and tectonic implications.Geophys.Res.Lett.,2006,33,L22303,doi:10． 1029/2006GL027717
[16] 刘洁,刘启元,郭飚等.中国境内天山上地幔小尺度对流与造山作用.中国科学(D辑),2007,37(6) :728～735 Liu J,Liu Q Y,Guo B,et al.Small-scale mantle convection and orogeny of Tienshan in China.Science in China (Series D) (in Chinese),2007,37(6) :728～735
[17] 许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5) :492～501 Xu Z H.A present-day tectonic stress map for Eastern Asia region.Acta Seismologica Sinica (in Chinese),2001,23(5) :492～501
[18] 杨少敏.李杰,王琪.GPS研究天山现今变形与断层活动.中国科学(D辑),2008,38(7) :872～880 Yang S M,Li J,Wang Q.The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations.Science in China (Series D) (in Chinese),2008,38(7) :872～880
[19] 郑斯华,高原.中国大陆岩石层的方位各向异性.地震学报,1994,16(2) :131～140 Zheng S H,Gao Y.The azimuthal anisotropy of rock layer in China mainland.Acta Seismologica Sinica (in Chinese),1994,16(2) :131～140
[20] 罗艳,黄忠贤,彭艳菊等.中国大陆及邻区SKS波分裂研究.地球物理学报,2004,47(5) :812～821 LuoY,HuangZX,Peng Y J,et al.A study on SKSwave splitting beneath the China mainland and adjacent regions.Chinese J.Geophys.(in Chinese),2004,47(5) :812～821
[21] 高原,滕吉文.中国大陆地壳与上地幔地震各向异性研究.地球物理学进展,2005,20(1) :180～185 Gao Y,Teng J W.Studies on seismic anisotropy in the crust and mantle on Chinese mainland.Progress in Geophysics (in Chinese),2005,20(1) :180～185
[22] Barruol G,Hoffmann R.Seismic anisotropy beneath the Geoscope stations from SKS splitting.J.Geophys.Res.,1999,104(B5) :10757～10774
[23] Chen Y P,Wang L S,Mi N,et al.Shear wave splitting observations in the Chinese Tianshan orogenic belt.Geophys.Res.Lett.,2005,32,L07306,doi:10． 1029/2004GL021686
[24] Vinnik L P,Aleshin I M,Kiselev S G.Depth localized azimuthal anisotropy from SKS and P receiver functions:The TienShan.Geophys.J.Int.,2007,169(3) :1289～1299
[25] Roecker S W.Constraints on the crust and upper mantle of the Kyrgyz Tien Shan from the preliminary analysis of CHENGIS broadband data.Russ.Geol.Geophys.,2001,42:1554～1565
[26] Li Y H,Wu Q J,Jiang L J,et al.Complex seismic anisotropic structure beneath the central Tien Shan revealed by shear wave splitting.Geophys.J.Int.,2010,181 (3) :1678～1686
[27] Gao S S,Liu K H.Significant seismic anisotropy beneath the southern Lhasa Terrane,Tibetan Plateau.Geochem.Geophys.Geosyst.,2009,10,Q02008,doi:10． 1029/2008GC002227
[28] W(u|¨)stefeld A,Bokelmann G H R.Null detection in shearwave splitting measurements.Bull.Seismol.Soc.Am.,2007,97(4) :1204～1211
[29] W(u|¨)stefeld A,Bokelmann G H R,Zaroli C,et al.SplitLab:a shear-wave splitting environment in Matlab.Comput.Geosci.,2008,34(5) :515～528
[30] Bowman J R,Ando M.Shear-wave splitting in the uppermantle wedge above the Tonga subduction zone.Geophys.J.R.Astron.Soc.,1987,88:25～41
[31] Silver P G,Chan W W.Shear wave splitting and subcontinental mantle deformation.J.Geophys.Res.,1991,96:16429～16454
[32] Vecsey L,Plomerova J,Babuska V.Shear-wave splitting measurements-Problems and solutions.Tectonophysics,2008,462:178～196
[33] Silver P G.Seismic anisotropy beneath the continents:probing the depth of geology.Annu.Rev.Earth Planet.Sci.,1996,24:385～432
[34] Levin V,Menke W,Park J.Shear-wave splitting in Appalachians:a case for multilayered anisotropy.J.Geophys.Res.,1999,104:17975～17994
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