四川地区壳幔结构剖面S波接收函数分析
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摘要
寻找青藏高原岩石圈热流物质向东流动的准确地震学证据及其动力学机制解释难点在于精确岩石圈厚度的求取.本文利用S波接收函数方法计算得到四川地区51个宽频台站的211个远震事件叠加接收函数,通过时深转换获得了该地区准确的地壳和岩石圈埋深分布.主要研究结果如下:四川地区地壳厚度变化范围为40～72 km,西藏的东部到四川盆地逐渐变薄,最厚的地方在雅江(YJI)地区,约为72 km,最薄的地方在盆地内部西充(XCO)地区,约为40 km,松潘-甘孜地块、川滇块体及滇中以北较厚,平均厚度为52～68 km,龙门山断裂西侧为55～60 km,四川盆地为40～50 km,存在10～15 km地壳厚度变化梯度;岩石圈埋深变化范围为100～180 km,整个四川地区表现出厚的四川盆地被薄的岩石圈环绕,外缘厚度为100～130 km,盆地内部为140～180 km,最厚的地方在"X"型断裂附近,呈现出"一凹两隆"的特征,最薄的地方是约100～120 km的龙门山断裂西侧及盆地西南部.建立的动力学模型为青藏高原东部热物质在向东流动的过程中被冷的、厚的、坚固的四川盆地阻挡,进而向东北和东南两个方向逃逸.
Lithospheric thickness is one of most important parameters to evaluate the earthquake evidence and dynamic mechanism of Tibetan plateau hot flow moving eastward.This paper obtains the stacking S receiver functions of 51 permanent broad-band stations and 211 teleseismic events records with the method of S receiver functions in Sichuan region,we get the depth distribution of the Moho and LAB through transformation of the depth in this region.The main results of the research are as follows:the Moho depth ranges from 40 to 72 km in Sichuan region,it becomes thinner from eastern Tibet to Sichuan Basin,the thickest crust is about 72 km,located in Yajiang region,the thinnest crust is about 40 km,located in Xichong region,the average depth ranges from 52 to 68 km beneath the Songpan-Ganze fold and Sichuan-Yunnan terrane,the crustal thickness is estimated to be 55~60 km beneath western Longmenshan fault system and about 40km beneath Sichuan Basin,forming a step of 10~15km.the LAB depth ranges from 100 to 180 km,western Sichuan Basin is found to be surrounded by a thinner lithosphere,the depth ranges from 100 to 130 km beneath the basin boundary as thick as to from 140 to 180 km,the thickest lithosphere is about 180 km near "X" fault system,appearing as "one depression and two uplifts",the thinnest lithosphere ranges from 100 to 120 km beneath western Longmenshan fault system and northwestern Sichuan Basin,at the same time,the lithosphere thickness near Huamashi ranges from 100 to 120 km.The last dynamic model of this paper is as follows:it is proved that a eastward preferential hot asthenosphere flow from Tibetan plateau is resisted by the cold thick rigid Sichuan Basin with Seismic evidence,thus branching into a northeastward and a southeastward one.
Lithospheric thickness is one of most important parameters to evaluate the earthquake evidence and dynamic mechanism of Tibetan plateau hot flow moving eastward.This paper obtains the stacking S receiver functions of 51 permanent broad-band stations and 211 teleseismic events records with the method of S receiver functions in Sichuan region,we get the depth distribution of the Moho and LAB through transformation of the depth in this region.The main results of the research are as follows:the Moho depth ranges from 40 to 72 km in Sichuan region,it becomes thinner from eastern Tibet to Sichuan Basin,the thickest crust is about 72 km,located in Yajiang region,the thinnest crust is about 40 km,located in Xichong region,the average depth ranges from 52 to 68 km beneath the Songpan-Ganze fold and Sichuan-Yunnan terrane,the crustal thickness is estimated to be 55~60 km beneath western Longmenshan fault system and about 40km beneath Sichuan Basin,forming a step of 10~15km.the LAB depth ranges from 100 to 180 km,western Sichuan Basin is found to be surrounded by a thinner lithosphere,the depth ranges from 100 to 130 km beneath the basin boundary as thick as to from 140 to 180 km,the thickest lithosphere is about 180 km near "X" fault system,appearing as "one depression and two uplifts",the thinnest lithosphere ranges from 100 to 120 km beneath western Longmenshan fault system and northwestern Sichuan Basin,at the same time,the lithosphere thickness near Huamashi ranges from 100 to 120 km.The last dynamic model of this paper is as follows:it is proved that a eastward preferential hot asthenosphere flow from Tibetan plateau is resisted by the cold thick rigid Sichuan Basin with Seismic evidence,thus branching into a northeastward and a southeastward one.
引文
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[12]杨海燕,胡家富,赵宏,等.川西地区壳幔结构与汶川M s 8.0级地震的孕震背景[J].地球物理学报,2009,52(2):356-364.
[13]LI X,KIND R,PRIESTLEY K,et al.Mapping the Ha-waiian plume conduit with converted seismic waves[J].Nature,2000,405,938-941.
[14]YUAN X,KIND R,LI X,et al.The s receiver function:synthetics and data example[J].Geophys J Int,2006,165,555-564.
[15]READING A,KENNET B,SAMBRIDGE M.2003.Im-proved inversion for seismic structure using trans-formed,s-wavevector receiver function:removing the effect of the free surface,Geophysical Res.Lett,30,No.19,doi:1029/2003GL018090,2003.
[16]HU Jia-fu,XU Xin-gqian,YANG Hai-yan,et al.S re-ceiver functions analysis of crustal and lithospheric structures beneath eastern Tibet,Earth Planet.Sci.Lett,306,77-85.
[17]HU Jia-fu,YANG Hai-yan,XU Xing-qian,et al.Lithos-pheric structure and crust-mantle decoupling in the southeast edge of theTibetan Plateau[J].Journal of Gondwana Research,2012,22:1060-1067.
[18]张洪双,田小波,滕吉文.接收函数方法估计Moho倾斜地区的地壳速度比[J].地球物理学报,2009,52(5):1243-1252.
[19]ZHANG Z J,WANG Y,CHEN Y,et al.2009.Crustal structure across longmenshan fault belt from passive source seismic profiling,Geophysical Res.Lett.,36,L17310,doi:10.1029/2009GL039580.
[20]ZHANG Z J,YUAN X H,CHEN Y,et al.Seismic sig-nature of the colision between the east Tibetan escape flow and the Sichuan Basin[J].Earth Planet Sci Lett,2010,292,254-264.
[21]KENNETT B L N,ENGDAHL E R.Traveltimes for global earthquake location and phase identification[J].Geophysical Journal International,1991,122,429-465.
[2]滕吉文,白登海,杨辉,等.2008汶川M s 8.0地震发生的深层过程和动力学响应[J].地球物理学报,2008,51(5):1385-1402.
[3]曾融生,孙为国.青藏高原岩石圈及其东部邻区的地震活动性和震源机制以及高原物质东流的讨论[J].地震学报,1992,14(增刊):523-533.
[4]张雪梅,孙若昧,滕吉文.青藏高原及其邻区地壳、岩石圈和软流层厚度研究[J].科学通报,2007,52(3):332-338.
[5]李昱,姚华建,刘启元,等.川西地区台阵环境噪声瑞利波相速度层析成像[J].地球物理学报,2010,53(4):842-852.
[6]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[J].地球物理学报,2009,52(2):346-355.
[7]楼海,王椿镛,等.2008年汶川M s 8.0级地震的深部构造环境[J].中国科学,2008,38(10):1207-1220.
[8]HU J F,HU Y L,XIA J Y,et al.Crust-mantle velocity structure of S wave and dynamic process beneath Burma Arc and its adjacent regions[J].Chinese J of Geophy,2008,51(1):105-114.
[9]HU Jia-fu,YANG Hai-yan,ZHAO Hong.Structure and Significance of S-wave velocity and Poisson’s ratio in crust beneath the eastern side of the Qinghai-Tibet plateau[J].Pure and Applied Geophysics,2008b,165:829-845.
[10]王辉,曹建玲,等.川滇地区下地壳流动对上地壳运动变形影响的数值模拟[J].地震学报,2007,29(6):582-591.
[11]徐强,赵俊猛,崔仲雄,等.利用接收函数研究青藏高原东南缘的地壳上地幔结构[J].地球物理学报,2009,52(12):3001-3008.
[12]杨海燕,胡家富,赵宏,等.川西地区壳幔结构与汶川M s 8.0级地震的孕震背景[J].地球物理学报,2009,52(2):356-364.
[13]LI X,KIND R,PRIESTLEY K,et al.Mapping the Ha-waiian plume conduit with converted seismic waves[J].Nature,2000,405,938-941.
[14]YUAN X,KIND R,LI X,et al.The s receiver function:synthetics and data example[J].Geophys J Int,2006,165,555-564.
[15]READING A,KENNET B,SAMBRIDGE M.2003.Im-proved inversion for seismic structure using trans-formed,s-wavevector receiver function:removing the effect of the free surface,Geophysical Res.Lett,30,No.19,doi:1029/2003GL018090,2003.
[16]HU Jia-fu,XU Xin-gqian,YANG Hai-yan,et al.S re-ceiver functions analysis of crustal and lithospheric structures beneath eastern Tibet,Earth Planet.Sci.Lett,306,77-85.
[17]HU Jia-fu,YANG Hai-yan,XU Xing-qian,et al.Lithos-pheric structure and crust-mantle decoupling in the southeast edge of theTibetan Plateau[J].Journal of Gondwana Research,2012,22:1060-1067.
[18]张洪双,田小波,滕吉文.接收函数方法估计Moho倾斜地区的地壳速度比[J].地球物理学报,2009,52(5):1243-1252.
[19]ZHANG Z J,WANG Y,CHEN Y,et al.2009.Crustal structure across longmenshan fault belt from passive source seismic profiling,Geophysical Res.Lett.,36,L17310,doi:10.1029/2009GL039580.
[20]ZHANG Z J,YUAN X H,CHEN Y,et al.Seismic sig-nature of the colision between the east Tibetan escape flow and the Sichuan Basin[J].Earth Planet Sci Lett,2010,292,254-264.
[21]KENNETT B L N,ENGDAHL E R.Traveltimes for global earthquake location and phase identification[J].Geophysical Journal International,1991,122,429-465.
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