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
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摘要
东构造结是印度板块和欧亚板块碰撞的奇点,历来是地学研究的热点.本文在中国及区域地震台网资料所得结果的基础上,增加了1964-2006年的ISC数据,总共349475个Pn波到时资料,着重反演了东构造结及周边地区Pn波速度结构和各向异性.结果表明该区Pn速度结构与现代构造活动存在较明显的关联:四川盆地,印度板块是构造稳定的地块而具有高速异常;藏东南和南北地震带构造活动强烈而显示低速异常,云南南部、中南半岛北部因处于缅甸弧弧后扩张区其低速异常尤为明显.Pn波各向异性表明快波方向在东构造结有一顺时针旋转的趋势:在藏东南是北东方向,然后在南北地震带先转向东南,再转向南,最后在中南半岛北部突变为近东西向.这是因为青藏高原物质在东流的过程中,相对于东构造结和四川盆地,在藏东南和南北地震带存在强烈的简单剪切变形,而在缅甸弧后扩张区为纯剪切变形所致.SKS快波方向也有类似的旋转趋势,但在中南半岛北部附近,具有近东西向Pn快波方向的区域,比云南南部东西向SKS区域偏南3°左右,这可能是由于该地区岩石圈上部运动比下部更快的结果.
The Eastern Himalayan Syntaxis (EHS) is a singular point of continental collision between the Indian and Eurasian plates, and has been focused by many geoscientists. We added the ISC data of 1964-2006 to previous data set, Chinese national and provincial events data used by Pei et al, and 349475 Pn arrivals were selected in all. We have obtained seismic velocities and anisotropy in the uppermost mantle around EHS and surrounding regions by performing tomographic inversion of Pn travel times. Comparing Pn velocity variation with geological results, we find they have distinct correlation; particularly high velocities always exist in old stable regions such as Sichuan Basin and Indian Plate. Low Pn velocities lie in active tectonic regions, volcanic areas and magmatic rock regions, for example, eastern Tibetan Plateau and North-South Seismic Zone, southern Yunnan province and northern Indochina. Pn anisotropy results show that the fast directions of Pn are clockwise around the EHS from NE in southeastern Tibetan Plateau, then SE to NS in North-South Seismic Zone. But the direction sharply changes to EW in the northern Indochina. The clockwise Pn fast direction maybe results from movement of mass extruded from Tibet under simple shear, which is caused by mass flow in southeastern Tibetan Plateau and North-South Seismic Zone relative to stable EHS and Sichuan Basin. The EW Pn direction probably results from pure shear, which is caused by compression in NS and extension in EW in Burma back-arc extensional area. The polarization directions of SKS have similar rotation to Pn, but in northern Indochina the oriented EW fast direction area of Pn has a southward offset of about 3° than SKS, which maybe results from the faster movement of upper lithosphere in this area.
The Eastern Himalayan Syntaxis (EHS) is a singular point of continental collision between the Indian and Eurasian plates, and has been focused by many geoscientists. We added the ISC data of 1964-2006 to previous data set, Chinese national and provincial events data used by Pei et al, and 349475 Pn arrivals were selected in all. We have obtained seismic velocities and anisotropy in the uppermost mantle around EHS and surrounding regions by performing tomographic inversion of Pn travel times. Comparing Pn velocity variation with geological results, we find they have distinct correlation; particularly high velocities always exist in old stable regions such as Sichuan Basin and Indian Plate. Low Pn velocities lie in active tectonic regions, volcanic areas and magmatic rock regions, for example, eastern Tibetan Plateau and North-South Seismic Zone, southern Yunnan province and northern Indochina. Pn anisotropy results show that the fast directions of Pn are clockwise around the EHS from NE in southeastern Tibetan Plateau, then SE to NS in North-South Seismic Zone. But the direction sharply changes to EW in the northern Indochina. The clockwise Pn fast direction maybe results from movement of mass extruded from Tibet under simple shear, which is caused by mass flow in southeastern Tibetan Plateau and North-South Seismic Zone relative to stable EHS and Sichuan Basin. The EW Pn direction probably results from pure shear, which is caused by compression in NS and extension in EW in Burma back-arc extensional area. The polarization directions of SKS have similar rotation to Pn, but in northern Indochina the oriented EW fast direction area of Pn has a southward offset of about 3° than SKS, which maybe results from the faster movement of upper lithosphere in this area.
引文
[1] Holt W E, Ni J F, Wallace T C, et al. The active tectonic of the eastern Himalayan Syntaxis and surrounding region. J.Geophys. Res. ,1991,96:14595-14632
[2] 熊熊,许厚泽,滕吉文.青藏高原物质东流的岩石层力学背景探讨.地壳形变与地震,200l,21(2) :1-7 Xiong X, Xu Z H, Teng J W. Investigation on lithospheric mechanical background of eastward mass flow of Tibet.Crustal Deformation and Earthquake (in Chinese), 2001,21(2) :1-7
[3] Wang Q, Zhang P Z, Freymueller J T, et al. Present-day crustal deformation in China constrained by global positioningsystem measurements. Science, 2001, 294:574-577
[4] 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, L( ) Z Y, et al. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern. Science in China (Series D ) (in Chinese), 2007 ,37(4) :495-503
[5] Sol S , Meltzer A, Burgmann R , et al. Geodynamics of the southeastern Tibetan Plateau from seismic anisotropy and geodesy. Geology, 2007,35(6) :563-566
[6] Pei S Y, Zhao J M, Sun Y S, et al. Upper mantle seismic velocities and anisotropy in China determined through Pn and Sn tomography. J.Geophys. Res., 2007 ,112: B05312 , doi:10． 1029/2006JB004409
[7] Nelson K D, Zhao W J, Brown L D. Partially molten middle crust beneath southern Tibet; synthesis of project INDEPTH results. Science, 1996,274; 1684-1688
[8] 丁志峰,曾融生,吴大铭.青藏高原的Pn波速度和Moho面的起伏.地震学报,1984,6:317-325 Ding Z F, Zeng R S, Wu D M. The Pn wave velocities and the relief of Moho in the Tibetan Plateau. Acta Seismologica Sinica (in Chinese) , 1984 ,6:317-325
[9] Hearn T M. Anisotropic Pn tomography in the western United States. J. Geophys. Res. ,1996,101:8403-8414
[10] Hearn T M, Beghoul N, Barazangi M. Tomography of the western United States from regional arrival time. J.Geophys. Res. ,1991,96:16369-16381
[11] 裴顺平.中国大陆上地幔顶部体波速度层析成像[博士论文].北京:中国地震局地球物理研究所,2002 Pei S P. Pn＆Sn Tomography of uppermost mantle in China [Ph. D. thesis]. Beijing: Institute of Geophysics, China Earthquake Administration, 2002
[12] Beghoul N, Barazangi M. Comment on "Lateral variations and azimulhal isotropy of Pn velocities beneath Basin and Range Province" by Lian-she Zhao. J. Geophys. Res. ,1995,100 : 12459-12461
[13] Hearn T M. Pn travel times in Southern California. J.Geophys. Res., 1984 ,89:1843-1855
[14] Hearn T M, Wang S Y, Ni J F, et al. Uppermost mantle velocities beneath China and surrounding regions. J.Geophys. Res., 2004． 109, B11301． doi: 10． 1029/2003JB002874
[15] 裴顺平,许忠淮,汪素云.中国及其邻区Pn波速度结构成因探讨.地震学报,2004,26(1) :1-10 Pei S P, Xu Z H, Wang S Y. Discussion on origin of Pn velocity variation in China and adjacent region. Acta Seismologica Sinica (in Chinese), 2004 ,26(1) : 1-10
[16] Wang C Y, HUANG-FU G. Crustal structure in Teng'chong volcanogeothermal Area, western Yunnan, China.Tectonophysics, 2004,380:6 9-87
[17] Lei J S, Zhao D P, Su Y J. Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data. J.Geophys. Res., 2009, 114, B05302, doi: 10． 1029/2008JB005881
[18] Huang J L, Zhao D P. High-resolution mantle tomography of China and surrounding regions. J. Geophys. Res. . 2006,111,B09305,doi:10． 1029/2005JB004066
[19] Nicolas A, Christensen N 1． Formation of anisotropy in upper mantle peridotite. In: Fuchs K, Froidevaux C, eds. Composition, Structure and Dynamics of the Lithosphere-Asthenosphere System. AGU, 1987 ,16:111-123
[20] Satyabala S P. Oblique plate convergence in the Indo-Burma (Myanmar) subduction region. Pure Appl. Geophys, 2003,160:1611-1650
[21] Li C, Robert D, R D ver der Hilst, et al. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma.Earthand Planetary Science Letters ,2008,274:157-168
[22] Yao H J, Beghein C, R D van der Hilst. Surface wave array tomography in SE Tibet from ambient seismic noise and two-station analysis-Ⅱ. Crustal and upper-mantle structure.Geophys. J. Int. , 2008,173:205-219
[23] Barazangi M, Ni J. Velocities and propagation characteristic of Pn and Sn beneath the Himalayan Arc and Tibetan plateau: Possible evidence for underthrusting of Indian continental lithosphere beneath Tibet. Geology, 1982, 10:179-185
[24] 苏伟,王椿镛,黄忠贤.青藏高原及邻区的Rayleigh面波的方位各向异性.中国科学(D辑),2008,38(6) :674-682 Su W, Wang C Y, Huang Z X. Rayleigh surface wave azimuthal anisotropy of Tibet and surround. Science in China (Series D) (in Chinese), 2008,38(6) :674-682
[25] Liang C T, Song X D. Tomographic inversion of Pn travel times in China. J. Geophys. Res. , 2004． 109, B11304,doi:10． 1029/2003JB002789
[26] 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),2003,33(增刊):1494-1501 Huang J L, Song X D, Wang S Y. Fine structure of Pn velocity beneath Sichuan-Yunnan region. Science in China (Series D) (in Chinese), 2003,22(Suppl. ) : 144-150
[27] 汪素云,Hearn T M,许忠淮.中国大陆上地幔顶部Pn速度结构.中国科学(D辑),2001,31(6) :449-55 Wang S Y, Hearn T M, Xu Z H. Velocity structure of uppermost mantle beneath China continent from Pn tomography. Science in China ( Series D ) C in Chinese),2001,31(6) :449-55
[28] 郭飚,刘启元,陈九辉等.川西龙门山及邻区地壳上地幔远震P波层析成像.地球物理学报,2009,52(2) :346-355 Guo B, Liu Q Y, Chen J H, et al. Teleseismic P-wave tomography of the crust and upper mantle in Longmenshan area, west Sichuan. Chinese J. Geophys. (in Chinese),2009,52(2) :346-355
[29] Silver P G. Seismic anisotropy beneath the continents:Probing the depths of geology. Annu. Rev. Earth and Planetary Science Letters. ,1996,24:385-432
[30] Hess H H. Seismic anisotropy of the uppermost mantle under oceans. Nature, 1964,203:629-631
[31] Hearn T M. Uppermost mantle velocities and anisotropy beneath Europe. J. Geophys. Res. , 1999,104(B7) ,15123-15139
[32] 许忠淮.东亚地区现今构造应力图的编制.地震学报,2001, 23(5) :492-501Xu Z H. A present-day tectonic stress map for eastern Asia region. ActaSeismologica Sinica (in Chinese) , 2001,23(5) :492-501
[33] Morley C K. Combined escape tectonics and subduction rollback-back arc extension: a model for the evolution of Teriary rift basins in Thailand, Malaysia and Laos. Journal of the Geological Society ,2001,158:461-474
[34] Gao X, Su Y L, Wang W M, et al. Lower-crust S-wave velocity beneath western Yunnan Province from waveform inversion of dense seismic observations. Terra Nova , 2009,21:105-110
[35] Royden L H, Burchfiel B C, King R W. et al. Surface deformation and lower crustal flow in eastern Tibet. Science,1997,276:788-790
[36] Ling B, Takashi I, Hitoshi K, et al. Upper mantle anisotropy beneath Indochina block and adjacent regions from shear-wave splitting analysis of Vietnam array data. Physics of the Earth and Planetary Interiors, 2009,176:33-43,doi:10． 1016/j. pepi. 2009． 03． 008
[37] 李延兴,杨国华,李智等中国大陆活动地块的运动与应变状态.中国科学(D辑),2003,33(增刊):65-81 Li Y X, Yang G H, Li Z, et al. Movement and strain condition of active blocks in the Chinese mainland. Science in China (Series D), 2003 ,46(Suppl. ) :82-106
[2] 熊熊,许厚泽,滕吉文.青藏高原物质东流的岩石层力学背景探讨.地壳形变与地震,200l,21(2) :1-7 Xiong X, Xu Z H, Teng J W. Investigation on lithospheric mechanical background of eastward mass flow of Tibet.Crustal Deformation and Earthquake (in Chinese), 2001,21(2) :1-7
[3] Wang Q, Zhang P Z, Freymueller J T, et al. Present-day crustal deformation in China constrained by global positioningsystem measurements. Science, 2001, 294:574-577
[4] 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, L( ) Z Y, et al. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern. Science in China (Series D ) (in Chinese), 2007 ,37(4) :495-503
[5] Sol S , Meltzer A, Burgmann R , et al. Geodynamics of the southeastern Tibetan Plateau from seismic anisotropy and geodesy. Geology, 2007,35(6) :563-566
[6] Pei S Y, Zhao J M, Sun Y S, et al. Upper mantle seismic velocities and anisotropy in China determined through Pn and Sn tomography. J.Geophys. Res., 2007 ,112: B05312 , doi:10． 1029/2006JB004409
[7] Nelson K D, Zhao W J, Brown L D. Partially molten middle crust beneath southern Tibet; synthesis of project INDEPTH results. Science, 1996,274; 1684-1688
[8] 丁志峰,曾融生,吴大铭.青藏高原的Pn波速度和Moho面的起伏.地震学报,1984,6:317-325 Ding Z F, Zeng R S, Wu D M. The Pn wave velocities and the relief of Moho in the Tibetan Plateau. Acta Seismologica Sinica (in Chinese) , 1984 ,6:317-325
[9] Hearn T M. Anisotropic Pn tomography in the western United States. J. Geophys. Res. ,1996,101:8403-8414
[10] Hearn T M, Beghoul N, Barazangi M. Tomography of the western United States from regional arrival time. J.Geophys. Res. ,1991,96:16369-16381
[11] 裴顺平.中国大陆上地幔顶部体波速度层析成像[博士论文].北京:中国地震局地球物理研究所,2002 Pei S P. Pn＆Sn Tomography of uppermost mantle in China [Ph. D. thesis]. Beijing: Institute of Geophysics, China Earthquake Administration, 2002
[12] Beghoul N, Barazangi M. Comment on "Lateral variations and azimulhal isotropy of Pn velocities beneath Basin and Range Province" by Lian-she Zhao. J. Geophys. Res. ,1995,100 : 12459-12461
[13] Hearn T M. Pn travel times in Southern California. J.Geophys. Res., 1984 ,89:1843-1855
[14] Hearn T M, Wang S Y, Ni J F, et al. Uppermost mantle velocities beneath China and surrounding regions. J.Geophys. Res., 2004． 109, B11301． doi: 10． 1029/2003JB002874
[15] 裴顺平,许忠淮,汪素云.中国及其邻区Pn波速度结构成因探讨.地震学报,2004,26(1) :1-10 Pei S P, Xu Z H, Wang S Y. Discussion on origin of Pn velocity variation in China and adjacent region. Acta Seismologica Sinica (in Chinese), 2004 ,26(1) : 1-10
[16] Wang C Y, HUANG-FU G. Crustal structure in Teng'chong volcanogeothermal Area, western Yunnan, China.Tectonophysics, 2004,380:6 9-87
[17] Lei J S, Zhao D P, Su Y J. Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data. J.Geophys. Res., 2009, 114, B05302, doi: 10． 1029/2008JB005881
[18] Huang J L, Zhao D P. High-resolution mantle tomography of China and surrounding regions. J. Geophys. Res. . 2006,111,B09305,doi:10． 1029/2005JB004066
[19] Nicolas A, Christensen N 1． Formation of anisotropy in upper mantle peridotite. In: Fuchs K, Froidevaux C, eds. Composition, Structure and Dynamics of the Lithosphere-Asthenosphere System. AGU, 1987 ,16:111-123
[20] Satyabala S P. Oblique plate convergence in the Indo-Burma (Myanmar) subduction region. Pure Appl. Geophys, 2003,160:1611-1650
[21] Li C, Robert D, R D ver der Hilst, et al. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma.Earthand Planetary Science Letters ,2008,274:157-168
[22] Yao H J, Beghein C, R D van der Hilst. Surface wave array tomography in SE Tibet from ambient seismic noise and two-station analysis-Ⅱ. Crustal and upper-mantle structure.Geophys. J. Int. , 2008,173:205-219
[23] Barazangi M, Ni J. Velocities and propagation characteristic of Pn and Sn beneath the Himalayan Arc and Tibetan plateau: Possible evidence for underthrusting of Indian continental lithosphere beneath Tibet. Geology, 1982, 10:179-185
[24] 苏伟,王椿镛,黄忠贤.青藏高原及邻区的Rayleigh面波的方位各向异性.中国科学(D辑),2008,38(6) :674-682 Su W, Wang C Y, Huang Z X. Rayleigh surface wave azimuthal anisotropy of Tibet and surround. Science in China (Series D) (in Chinese), 2008,38(6) :674-682
[25] Liang C T, Song X D. Tomographic inversion of Pn travel times in China. J. Geophys. Res. , 2004． 109, B11304,doi:10． 1029/2003JB002789
[26] 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),2003,33(增刊):1494-1501 Huang J L, Song X D, Wang S Y. Fine structure of Pn velocity beneath Sichuan-Yunnan region. Science in China (Series D) (in Chinese), 2003,22(Suppl. ) : 144-150
[27] 汪素云,Hearn T M,许忠淮.中国大陆上地幔顶部Pn速度结构.中国科学(D辑),2001,31(6) :449-55 Wang S Y, Hearn T M, Xu Z H. Velocity structure of uppermost mantle beneath China continent from Pn tomography. Science in China ( Series D ) C in Chinese),2001,31(6) :449-55
[28] 郭飚,刘启元,陈九辉等.川西龙门山及邻区地壳上地幔远震P波层析成像.地球物理学报,2009,52(2) :346-355 Guo B, Liu Q Y, Chen J H, et al. Teleseismic P-wave tomography of the crust and upper mantle in Longmenshan area, west Sichuan. Chinese J. Geophys. (in Chinese),2009,52(2) :346-355
[29] Silver P G. Seismic anisotropy beneath the continents:Probing the depths of geology. Annu. Rev. Earth and Planetary Science Letters. ,1996,24:385-432
[30] Hess H H. Seismic anisotropy of the uppermost mantle under oceans. Nature, 1964,203:629-631
[31] Hearn T M. Uppermost mantle velocities and anisotropy beneath Europe. J. Geophys. Res. , 1999,104(B7) ,15123-15139
[32] 许忠淮.东亚地区现今构造应力图的编制.地震学报,2001, 23(5) :492-501Xu Z H. A present-day tectonic stress map for eastern Asia region. ActaSeismologica Sinica (in Chinese) , 2001,23(5) :492-501
[33] Morley C K. Combined escape tectonics and subduction rollback-back arc extension: a model for the evolution of Teriary rift basins in Thailand, Malaysia and Laos. Journal of the Geological Society ,2001,158:461-474
[34] Gao X, Su Y L, Wang W M, et al. Lower-crust S-wave velocity beneath western Yunnan Province from waveform inversion of dense seismic observations. Terra Nova , 2009,21:105-110
[35] Royden L H, Burchfiel B C, King R W. et al. Surface deformation and lower crustal flow in eastern Tibet. Science,1997,276:788-790
[36] Ling B, Takashi I, Hitoshi K, et al. Upper mantle anisotropy beneath Indochina block and adjacent regions from shear-wave splitting analysis of Vietnam array data. Physics of the Earth and Planetary Interiors, 2009,176:33-43,doi:10． 1016/j. pepi. 2009． 03． 008
[37] 李延兴,杨国华,李智等中国大陆活动地块的运动与应变状态.中国科学(D辑),2003,33(增刊):65-81 Li Y X, Yang G H, Li Z, et al. Movement and strain condition of active blocks in the Chinese mainland. Science in China (Series D), 2003 ,46(Suppl. ) :82-106
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