甘肃天水地区地壳上部二维速度结构成像研究
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摘要
利用有限差分和不规则网格最小二乘正反演算法,对青藏高原东北缘暨西秦岭天水-武都地区两条高分辨人工地震测深剖面的Pg波走时进行层析成像反演,结果显示该区基底界面起伏较大,构造复杂,断裂丰富、较陡且延伸较大,多数断层切割基底.礼县—西和之间的低速异常反映了沉积盆地的结构特征,结晶基底深度在5km左右.武山以东速度等值线横向变化明显,表现为褶皱.成县盆地速度变化平缓且速度值相对较高,基底埋深较浅,深度不到3km.礼县附近存在一条近南北断裂,5km深度以下有明显的上涌低速异常,可能为青藏高原深部幔源物质上升的通道.
We used the Pg-wave arrival times from high-resolution active-source seismic sounding to carry out the tomographic job on the northeastern margin of Qinghai-Tibet plateau,that is,the Tianshui-Wudu area in West Qinling,with finite difference forward and least squares inversing algorithm with irregular meshes.The results indicate that the study area has rich and complex fractures,such as the fluctuant basement and the steep faults mostly extending to great depths and cutting through the basement.The low-velocity zone between Lixian and Xihe reflects the existence of Xi-Li sedimentary basin,the basement of which is about 5 km deep.The pronounced changing of the velocity contour on the east of Wushan is consistent with the fold region nearby.The Chengxian basin has a relatively high and gently changing velocity,the basement depth of which is less than 3 km.Near Lixian there is a near north-south fault,and a low-velocity zone exists beneath about 5 km depth in the tomographic profile,which may be the upwelling channel of the deep mantle substance in the Tibetan Plateau.
We used the Pg-wave arrival times from high-resolution active-source seismic sounding to carry out the tomographic job on the northeastern margin of Qinghai-Tibet plateau,that is,the Tianshui-Wudu area in West Qinling,with finite difference forward and least squares inversing algorithm with irregular meshes.The results indicate that the study area has rich and complex fractures,such as the fluctuant basement and the steep faults mostly extending to great depths and cutting through the basement.The low-velocity zone between Lixian and Xihe reflects the existence of Xi-Li sedimentary basin,the basement of which is about 5 km deep.The pronounced changing of the velocity contour on the east of Wushan is consistent with the fold region nearby.The Chengxian basin has a relatively high and gently changing velocity,the basement depth of which is less than 3 km.Near Lixian there is a near north-south fault,and a low-velocity zone exists beneath about 5 km depth in the tomographic profile,which may be the upwelling channel of the deep mantle substance in the Tibetan Plateau.
引文
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[17]莫宣学,赵志丹,邓晋福等.青藏新生代钾质火山活动的时空迁移及向东部玄武岩省的过渡:壳幔深部物质流的暗示.现代地质,2007,21(2):255-264.Mo X X,Zhao Z D,Deng J F,et al.Migration of theTibetan enozoic potassic volcanism and its transition toeastern basaltic province:Implications for crustal and mantleflow.Geoscience(in Chinese),2007,21(2):255-264.
[18]Bijwaard H,Spakman W,Engdahl E R.Closing the gapbetween regional and global travel time tomography.J.Geophys.Res.,1998,103(B12):30055-30078.
[19]邹谨敞,吴增益.甘肃地震构造.//马杏垣等主编.中国岩石圈动力学图集.北京:中国地图出版社,1989.Zou J C,Wu Z Y.Seismic structure in Gansu.//Ma X Yeds.Atlas of the Lithospheric Dynamics in China(inChinese).Beijing:China Cartographic Publishing House,1989.
[20]喻学惠,张春福.甘肃西秦岭新生代碱性火山岩的Sr-Nd同位素及微量元素地球化学特征.地学前缘,1998,5(4):319-328.Yu X H,Zhang C F.Sr-Nd isotope and trace elementsgeochemical features of the Cenozoic volcanic rocks from WestQinling,Gansu Province.Earth Science Frontiers(inChinese),1998,5(4):319-328.
[21]喻学惠,莫宣学,苏尚国等.甘肃礼县新生代火山喷发碳酸岩的发现及意义.岩石学报,2003,19(1):105-112.Yu X H,Mo X X,Su S G,et al.Discovery and significance ofCenozoic volcanic carbonatite in Lixian,Gansu Province.ActaPetrologica Sinica(in Chinese),2003,19(1):105-112.
[2]裴先治,丁仨平,李佐臣等.西秦岭北缘早古生代天水—武山构造带及其构造演化.地质学报,2009,83(11):1547-1564.Pei X Z,Ding S P,Li Z C,et al.Early paleozoic Tianshui-Wudu tectonic zone of the northern margin of west Qinlingand its tectonic evolution.Acta Geologica Sinica(inChinese),2009,83(11):1547-1564.
[3]熊熊,滕吉文.青藏高原东缘地壳运动与深部过程的研究.地球物理学报,2007,45(4):507-515.Xiong X,Teng J W.Study on crustal movement and deepprocess in eastern Qinghai-Xizang Plateau.Chinese J.Geophys.(in Chinese),2007,45(4):507-515.
[4]梁中华,唐建民,滕智猛等.天水地震区地壳浅层速度结构.西北地震学报,1991,13(增刊):16-21.Liang Z H,Tang J M,Teng Z M,et al.The velocitystructure of shallow crust in Tianshui earthquake area.Northwestern Seismological Journal(in Chinese),1991,13(Supp):16-21.
[5]闵祥仪,周民都,郭健康等.灵台—阿木去乎剖面地壳速度结构.西北地震学报,1991,13(增刊):32-39.Min X Y,Zhou M D,Guo J K,et al.The crustal velocitystructure in Lingtai-Amuquhu profile.Northwestern SeismologicalJournal(in Chinese),1991,13(S1):32-39.
[6]李清河,闵祥林,郭健康等.天水—礼县地区地壳速度结构.西北地震学报,1991,(2):51-60.Li Q H,Min X L,Guo J K,et al.The crustal velocitystructure in Tianshui-Lixian region.Northwestern SeismologicalJournal(in Chinese),1991,(2):51-60.
[7]李清河,郭建康,周民都等.成县—西吉剖面地壳速度结构.西北地震学报,1991,13(S1):40-46.Li Q H,Guo J K,Zhou M D,et al.The velocity structure ofChengxian-Xiji profile.Northwestern Seismological Journal(in Chinese),1991,13(S1):40-46.
[8]郭守年,董志平,蒋梅等.天水地震区综合地球物理剖面的建立与壳幔结构.西北地震学报,1997,19(3):44-51.Guo S N,Dong Z P,Jiang M,et al.Establishment ofcomprehensive geophysical section and crust mantle structurein Tianshui earthquake area.Northwestern SeismologicalJournal(in Chinese),1997,19(3):44-51.
[9]林长佑,武玉霞,杨长福等.天水地区深部构造走向及区域应力场.地震研究,1996,19(2):175-183.Lin C Y,Wu Y X,Yang C F,et al.Strike of deep structureand regional stress field in Tianshui area.Journal ofSeismological Research(in Chinese),1996,19(2):175-183.
[10]Vidale J E.Finite-difference calculation of travel time.Bull.Seis.Soc.Am.,1988,78(6):2062-2076.
[11]Vidale J E.Finite-difference calculation of traveltimes inthree dimensions.Geophysics,1990,55(5):521-526.
[12]Hole J A.Nonlinear high-resolution three-dimensionalseismic travel time tomography.Journal of GeophysicalResearch,1992,97(B5):6553-6562.
[13]Hole J A,Brocher T M,Klemperer S L,et al.Three-dimensional seismic velocity structure of the San FranciscoBay area.J.Geophys.Res.,2000,105(13):859-874.
[14]Hole J A,Zelt C A,Pratt R G.Advances in controlled-source seismic imaging.Eos,2005,86(18):177-181.
[15]Hole J A,Zelt C A.3-D finite-difference reflectiontraveltimes.Geophys.J.Int.,1995,121(2):427-434.
[16]Paige C C,Saunders M A.LSQR:An Algorithm for SparseLinear Equations and Sparse Least Squares.ACM Trans.Math.Softw.,1982,8(1):43-71.
[17]莫宣学,赵志丹,邓晋福等.青藏新生代钾质火山活动的时空迁移及向东部玄武岩省的过渡:壳幔深部物质流的暗示.现代地质,2007,21(2):255-264.Mo X X,Zhao Z D,Deng J F,et al.Migration of theTibetan enozoic potassic volcanism and its transition toeastern basaltic province:Implications for crustal and mantleflow.Geoscience(in Chinese),2007,21(2):255-264.
[18]Bijwaard H,Spakman W,Engdahl E R.Closing the gapbetween regional and global travel time tomography.J.Geophys.Res.,1998,103(B12):30055-30078.
[19]邹谨敞,吴增益.甘肃地震构造.//马杏垣等主编.中国岩石圈动力学图集.北京:中国地图出版社,1989.Zou J C,Wu Z Y.Seismic structure in Gansu.//Ma X Yeds.Atlas of the Lithospheric Dynamics in China(inChinese).Beijing:China Cartographic Publishing House,1989.
[20]喻学惠,张春福.甘肃西秦岭新生代碱性火山岩的Sr-Nd同位素及微量元素地球化学特征.地学前缘,1998,5(4):319-328.Yu X H,Zhang C F.Sr-Nd isotope and trace elementsgeochemical features of the Cenozoic volcanic rocks from WestQinling,Gansu Province.Earth Science Frontiers(inChinese),1998,5(4):319-328.
[21]喻学惠,莫宣学,苏尚国等.甘肃礼县新生代火山喷发碳酸岩的发现及意义.岩石学报,2003,19(1):105-112.Yu X H,Mo X X,Su S G,et al.Discovery and significance ofCenozoic volcanic carbonatite in Lixian,Gansu Province.ActaPetrologica Sinica(in Chinese),2003,19(1):105-112.
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