华北北部地区地壳三维P波速度结构的双差地震层析成像
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摘要
利用区域固定台站和华北科学探测台阵记录的10 461个近震事件的183 909个Pg波绝对走时和495 753个相对走时数据,采用双差地震层析成像获得华北北部(37.5°～41.5°N,111.5°～119.5°E)范围内的地壳三维P波速度结构模型。结果表明:研究区内各主要构造单元具有明显不同的速度结构特征,速度异常的走向与区域构造的走向一致,浅层速度图像很好地反映了地表地质和岩性的变化;重定位后的大部分地震集中在0～20km的深度上,主要位于低速区的内部或高速和低速区的交界部位;三河—平谷和唐山地震震源区中、下地壳的低速异常可能是流体的显示。结合前人成果和本文模型所揭示的深、浅结构,我们认为太平洋板块在中国东部之下的俯冲和滞留引起板块脱水、软流圈物质上涌等一系列过程,软流圈热物质到达上地幔顶部并沿超壳断裂上侵进入地壳,致使上地幔顶部和下地壳中的含水矿物发生脱水作用产生流体,流体继续上移造成中、上地壳发震层的弱化,从而导致大地震的发生。因此华北北部地区的强震活动,以及地壳结构的非均匀性应是与太平洋板块俯冲、滞留引起的深部过程密切相关的。
We determined a 3D P-wave velocity model of the crust under the northern part of North China(37.5°～41.5°N,111.5°～119.5°E)by using double-difference seismic tomography and jointly inverting 183 909 absolute arrival times and 495 753 differential arrival times from 10 461 local events recorded by permanent seismic network and North China Seismic Array.Our results show considerable differences in the velocity structure of the upper crust between the main tectonic units in the study area.The trends of velocity anomalies are consistent with the trends of geological structures.The velocity images of the upper crust reflect well the surface geological and lithology features.The majority of hypocenters is located between 0～20km depth and located in the low velocity anomalies or in the conjunctional areas of low and high velocity anomalies.Significant low velocity anomalies are found in the source areas of the 1976 Tangshan earthquake(M7.8)and the1679Sanhe-Pinggu earthquake(M8.0),which are considered to be associated with fluids.Combining previous studies with our present model,we think that the deep subduction and stagnancy of the Pacific slab have resulted in deep slab dehydration and upwelling of hot asthenospheric materials,and the asthenospheric materials have reached the top of uppermantle and broken into crust along the deep faults which may cut through the crust,then the hydrous minerals in the top of uppermantle and lower crust are dehydrated to produce fluids,and these fluids further cause the weakening of the seismogenic layer in the middle and upper crust.Hence,we believe that the crustal heterogeneity and the seismotectonics under the northern part of North China are closely related to a series of deep dynamic processes associated with the deep subduction and stagnancy of the Pacific slab under East China.
We determined a 3D P-wave velocity model of the crust under the northern part of North China(37.5°～41.5°N,111.5°～119.5°E)by using double-difference seismic tomography and jointly inverting 183 909 absolute arrival times and 495 753 differential arrival times from 10 461 local events recorded by permanent seismic network and North China Seismic Array.Our results show considerable differences in the velocity structure of the upper crust between the main tectonic units in the study area.The trends of velocity anomalies are consistent with the trends of geological structures.The velocity images of the upper crust reflect well the surface geological and lithology features.The majority of hypocenters is located between 0～20km depth and located in the low velocity anomalies or in the conjunctional areas of low and high velocity anomalies.Significant low velocity anomalies are found in the source areas of the 1976 Tangshan earthquake(M7.8)and the1679Sanhe-Pinggu earthquake(M8.0),which are considered to be associated with fluids.Combining previous studies with our present model,we think that the deep subduction and stagnancy of the Pacific slab have resulted in deep slab dehydration and upwelling of hot asthenospheric materials,and the asthenospheric materials have reached the top of uppermantle and broken into crust along the deep faults which may cut through the crust,then the hydrous minerals in the top of uppermantle and lower crust are dehydrated to produce fluids,and these fluids further cause the weakening of the seismogenic layer in the middle and upper crust.Hence,we believe that the crustal heterogeneity and the seismotectonics under the northern part of North China are closely related to a series of deep dynamic processes associated with the deep subduction and stagnancy of the Pacific slab under East China.
引文
[1]刘国栋,史书林,王宝钧.华北地区壳内高导层及其与地壳构造活动性的关系[J].中国科学(B辑),1984,9:839-848.
[2] Huang J,Zhao D.Crustal heterogeneity and seismotectonics of the region around Beijing,China[J].Tectonophysics,2004,385:159-180.
[3]齐诚,赵大鹏,陈颙.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系[J].地球物理学报,2006,49(3):805-815.
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[6] Zhao D,Negishi H.The 1995Kobe earthquake:Seismic image of the source zone and its implications for the rupture nucleation[J].J Geophys Res,1998,103:9 967-9 986.
[7] Huang J,Zhao D.High-resolution mantle tomography of China and surrounding regions[J].J Geophys Res,2006,111:B09305.
[8] Zhao D.Global tomographic images of mantle plumes and subducting slabs:insight into deep Earth dynamics[J].Phys earth planet in,2004,146:3-34.
[9] Huang J,Zhao D.Seismic imaging of the crust and upper mantle under Beijing and surrounding regions[J].Phys earth planet in,2009,173:330-348.
[10] Tian Y,Zhao D,Sun R,et al.Seismic imaging of the crust and upper mantle beneath the North China Craton[J].Phys earth planet in,2009,172:169-182.
[11] Zhao D,Tian Y,Lei J,et al.Seismic image and origin of the Changbai intraplate volcano in East Asia:role of big mantle wedge above the stagnant Pacific slab[J].Phys earth planet in,2009,173:197-206.
[12] Zhao D,Yu S,Ohtani E.East Asia:seismotectonics,magmatism and mantle dynamics[J].Journal of Asian Earth Sciences,2011,40:689-709.
[13] Zhang H,Thurber C.Double-difference tomography:the method and its application to the Hayward Fault,California[J].Bull Seism Soc Am,2003,93(5):1 875-1 889.
[14]Waldhauser F,Ellsworth W L.A double-difference earthquake location algorithm:Method and application to the northern Hayward Fault,California[J].Bull Seism Soc Am,2000,90(6):1 353-1 368.
[15]任清芳,张成科,张先康,等.八达岭及周缘地区壳幔结构与潜在震源探讨[J].西北地震学报,1997,19(3):56-62.
[16]张成科,张先康,盖玉杰,等.文安—蔚县—察右中旗剖面地壳上地幔速度结构与构造研究[J].华北地震科学,1997,15(3):18-28.
[17]祝治平,张先康,张建狮,等.北京—怀来—丰镇剖面地壳上地幔构造与速度结构研究[J].地震学报,1997,19(5):499-505.
[18]赵金仁,张先康,张成科,等.香河—北京—涿鹿及其相邻地区壳幔构造与速度结构特征[J].地震地质,1999,21(1):29-36.
[19]赵金仁,张先康,张成科,等.利用宽角反射/折射和深反射探测剖面揭示三河—平谷大震区深部结构特征[J].地球物理学报,2004,47(4):646-653.
[20]赵金仁,张先康,张成科,等.北京西北地区壳幔结构的非均匀性特征与地震活动[J].地震学报,2005,27(2):119-127.
[21]王帅军,张先康,方盛明,等.渤海湾西北缘及其邻近地区地壳结构与构造特征[J].地球物理学报,2008,51(5):1 451-1 458.
[22]嘉世旭,张成科,赵金仁,等.华北东北部裂陷盆地与燕山隆起地壳结构[J].地球物理学报,2009,52(1):99-110.
[23] Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares[J].Acm Transactions on Mathematical Software,1982,8(1):43-71.
[24] Thurber C,Eberhart-Phillips D.Local earthquake tomography with flexible gridding[J].Computers&Geosciences,1999,25(7):809-818.
[25] Scarfi L,Giampiccolo E,Musumeci C,et al.New insights on 3Dcrustal structure in southeastern Sicily(Italy)and tectonic implications from an adaptive mesh seismic tomography[J].Phys earth planet in,2007,161:74-85.
[26]潘佳铁,吴庆举,李永华,等.华北地区瑞雷面波相速度层析成像[J].地球物理学报,2011,54(1):67-76.
[27] Fang L,Wu J,Ding Z,et al.High resolution Rayleigh wave group velocity tomography in NorthChina from ambient seismic noise[J].Geophys J Inter,2010,181(2):1 171-1 182.
[28]杨峰,黄金莉.首都圈上地壳高精度三维P波速度模型——基于石油地震叠加速度和人工地震测深剖面[J].地球物理学报,2013,56(5):1 487-1 496.
[29]刘启元,王峻,陈九辉,等.1976年唐山大地震的孕震环境:密集地震台阵观测得到的结果[J].地学前缘(中国地质大学(北京);北京大学),2007,14(6):205-213.
[30]嘉世旭,齐诚,王夫运,等.首都圈地壳网格化三维结构[J].地球物理学报,2005,48(6):1 316-1 324.
[31]李乐,陈棋福,陈颙.首都圈地震活动构造成因的小震精定位分析[J].地球物理学进展,2007,22(1):24-34.
[32]刘昌铨,嘉世旭.唐山地震区地壳上地幔结构特征:二维非均匀介质中理论地震图计算和结果分析[J].地震学报,1986,8:341-353.
[33] Wang J,Zhao D,Yao Z.Crustal and uppermost mantle structure and seismotectonics of North China Craton[J].Tectonophysics,2013,582:177-187.
[34] Zhao D,Santosh M,Yamada A.Dissecting large earthquakes in Japan:role of arc magma and fluids[J].Island Arc,2010,19:4-16.
[35]刘保金,曲国胜,孙铭心,等.唐山地震区地壳结构和构造:深地震反射剖面结果[J].地震地质,2011,33:383-397.
[36]刘保金,张先康,陈颙,等.三河—平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面[J].地球物理学报,2011,54(5):1 251-1 259.
[37]王椿镛,吴庆举,段永红,等.华北地壳上地幔结构及其大地震深部构造成因[J].中国科学:地球科学,2017,47:684-719.
[38]杨峰,黄金莉,杨挺.应用远震有限频率层析成像反演首都圈上地幔速度结构[J].地球物理学报,2010,53(8):1 806-1 816.
[39] Tian Y,Zhao D.Destruction mechanism of the North China Craton:Insight from P and S wave mantle tomography[J].Journal of Asian Earth Sciences,2011,42:1 132-1 145.
[40]翟明国.华北克拉通中生代破坏前的岩石圈地慢与下地壳[J].岩石学报,2008,24(10):2 185-2 204.
[41] Zhao D,Isozaki Y,Maruyama S.Seismic imaging of the Asian orogens and subduction zones[J].Journal of Asian Earth Sciences,2017,145:349-367.
[42] Lei J,Zhao D.Structural heterogeneity of the Longmenshan fault zone and the mechanism of the2008 Wenchuan earthquake(MS8.0)[J].Geochemistry Geophysics Geosystems,2009,10:Q10010.
[43]李大虎,吴萍萍,丁志峰.四川芦山MS7.0地震震源区及其周边区域P波三维速度结构研究[J].地震学报,2015,37(3):371-385.
[44]张洪双,田小波,刘芳,等.呼包盆地周缘壳、幔结构研究[J].地球物理学进展,2009,24(5):1 609-1 615.
[45]王新胜,方剑,许厚泽,等.华北克拉通岩石圈三维密度结构[J].地球物理学报,2012,55(4):1 154-1 160.
[46]酆少英,刘保金,姬计法,等.呼和浩特——包头盆地岩石圈细结构的深地震反射探测[J].地球物理学报,2015,58(4):1 158-1 168.
[47]李志伟,郝天珧,徐亚.华北克拉通上地幔顶部构造特征:来自台站间Pn波到时差成像的约束[J].科学通报,2011,56(12):962-970.
[48]Wessel P,Smith W H F.New improved version of Generic Mapping Tools released[J].EOS,Transactions,American Geophysical Union,1995,79(47):579.
[2] Huang J,Zhao D.Crustal heterogeneity and seismotectonics of the region around Beijing,China[J].Tectonophysics,2004,385:159-180.
[3]齐诚,赵大鹏,陈颙.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系[J].地球物理学报,2006,49(3):805-815.
[4] Lei J,Xie F,Lan C,et al.Seismic images under the Beijing region inferred from P and PmP data[J].Phys earth planet in,2008,168:134-146.
[5] Zhao D,Kanamori H,Negishi H,et al.Tomography of the source area of the 1995Kobe earthquake:evidence for fluids at the hypocenter?[J].Science,1996,274:1 891-1 894.
[6] Zhao D,Negishi H.The 1995Kobe earthquake:Seismic image of the source zone and its implications for the rupture nucleation[J].J Geophys Res,1998,103:9 967-9 986.
[7] Huang J,Zhao D.High-resolution mantle tomography of China and surrounding regions[J].J Geophys Res,2006,111:B09305.
[8] Zhao D.Global tomographic images of mantle plumes and subducting slabs:insight into deep Earth dynamics[J].Phys earth planet in,2004,146:3-34.
[9] Huang J,Zhao D.Seismic imaging of the crust and upper mantle under Beijing and surrounding regions[J].Phys earth planet in,2009,173:330-348.
[10] Tian Y,Zhao D,Sun R,et al.Seismic imaging of the crust and upper mantle beneath the North China Craton[J].Phys earth planet in,2009,172:169-182.
[11] Zhao D,Tian Y,Lei J,et al.Seismic image and origin of the Changbai intraplate volcano in East Asia:role of big mantle wedge above the stagnant Pacific slab[J].Phys earth planet in,2009,173:197-206.
[12] Zhao D,Yu S,Ohtani E.East Asia:seismotectonics,magmatism and mantle dynamics[J].Journal of Asian Earth Sciences,2011,40:689-709.
[13] Zhang H,Thurber C.Double-difference tomography:the method and its application to the Hayward Fault,California[J].Bull Seism Soc Am,2003,93(5):1 875-1 889.
[14]Waldhauser F,Ellsworth W L.A double-difference earthquake location algorithm:Method and application to the northern Hayward Fault,California[J].Bull Seism Soc Am,2000,90(6):1 353-1 368.
[15]任清芳,张成科,张先康,等.八达岭及周缘地区壳幔结构与潜在震源探讨[J].西北地震学报,1997,19(3):56-62.
[16]张成科,张先康,盖玉杰,等.文安—蔚县—察右中旗剖面地壳上地幔速度结构与构造研究[J].华北地震科学,1997,15(3):18-28.
[17]祝治平,张先康,张建狮,等.北京—怀来—丰镇剖面地壳上地幔构造与速度结构研究[J].地震学报,1997,19(5):499-505.
[18]赵金仁,张先康,张成科,等.香河—北京—涿鹿及其相邻地区壳幔构造与速度结构特征[J].地震地质,1999,21(1):29-36.
[19]赵金仁,张先康,张成科,等.利用宽角反射/折射和深反射探测剖面揭示三河—平谷大震区深部结构特征[J].地球物理学报,2004,47(4):646-653.
[20]赵金仁,张先康,张成科,等.北京西北地区壳幔结构的非均匀性特征与地震活动[J].地震学报,2005,27(2):119-127.
[21]王帅军,张先康,方盛明,等.渤海湾西北缘及其邻近地区地壳结构与构造特征[J].地球物理学报,2008,51(5):1 451-1 458.
[22]嘉世旭,张成科,赵金仁,等.华北东北部裂陷盆地与燕山隆起地壳结构[J].地球物理学报,2009,52(1):99-110.
[23] Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares[J].Acm Transactions on Mathematical Software,1982,8(1):43-71.
[24] Thurber C,Eberhart-Phillips D.Local earthquake tomography with flexible gridding[J].Computers&Geosciences,1999,25(7):809-818.
[25] Scarfi L,Giampiccolo E,Musumeci C,et al.New insights on 3Dcrustal structure in southeastern Sicily(Italy)and tectonic implications from an adaptive mesh seismic tomography[J].Phys earth planet in,2007,161:74-85.
[26]潘佳铁,吴庆举,李永华,等.华北地区瑞雷面波相速度层析成像[J].地球物理学报,2011,54(1):67-76.
[27] Fang L,Wu J,Ding Z,et al.High resolution Rayleigh wave group velocity tomography in NorthChina from ambient seismic noise[J].Geophys J Inter,2010,181(2):1 171-1 182.
[28]杨峰,黄金莉.首都圈上地壳高精度三维P波速度模型——基于石油地震叠加速度和人工地震测深剖面[J].地球物理学报,2013,56(5):1 487-1 496.
[29]刘启元,王峻,陈九辉,等.1976年唐山大地震的孕震环境:密集地震台阵观测得到的结果[J].地学前缘(中国地质大学(北京);北京大学),2007,14(6):205-213.
[30]嘉世旭,齐诚,王夫运,等.首都圈地壳网格化三维结构[J].地球物理学报,2005,48(6):1 316-1 324.
[31]李乐,陈棋福,陈颙.首都圈地震活动构造成因的小震精定位分析[J].地球物理学进展,2007,22(1):24-34.
[32]刘昌铨,嘉世旭.唐山地震区地壳上地幔结构特征:二维非均匀介质中理论地震图计算和结果分析[J].地震学报,1986,8:341-353.
[33] Wang J,Zhao D,Yao Z.Crustal and uppermost mantle structure and seismotectonics of North China Craton[J].Tectonophysics,2013,582:177-187.
[34] Zhao D,Santosh M,Yamada A.Dissecting large earthquakes in Japan:role of arc magma and fluids[J].Island Arc,2010,19:4-16.
[35]刘保金,曲国胜,孙铭心,等.唐山地震区地壳结构和构造:深地震反射剖面结果[J].地震地质,2011,33:383-397.
[36]刘保金,张先康,陈颙,等.三河—平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面[J].地球物理学报,2011,54(5):1 251-1 259.
[37]王椿镛,吴庆举,段永红,等.华北地壳上地幔结构及其大地震深部构造成因[J].中国科学:地球科学,2017,47:684-719.
[38]杨峰,黄金莉,杨挺.应用远震有限频率层析成像反演首都圈上地幔速度结构[J].地球物理学报,2010,53(8):1 806-1 816.
[39] Tian Y,Zhao D.Destruction mechanism of the North China Craton:Insight from P and S wave mantle tomography[J].Journal of Asian Earth Sciences,2011,42:1 132-1 145.
[40]翟明国.华北克拉通中生代破坏前的岩石圈地慢与下地壳[J].岩石学报,2008,24(10):2 185-2 204.
[41] Zhao D,Isozaki Y,Maruyama S.Seismic imaging of the Asian orogens and subduction zones[J].Journal of Asian Earth Sciences,2017,145:349-367.
[42] Lei J,Zhao D.Structural heterogeneity of the Longmenshan fault zone and the mechanism of the2008 Wenchuan earthquake(MS8.0)[J].Geochemistry Geophysics Geosystems,2009,10:Q10010.
[43]李大虎,吴萍萍,丁志峰.四川芦山MS7.0地震震源区及其周边区域P波三维速度结构研究[J].地震学报,2015,37(3):371-385.
[44]张洪双,田小波,刘芳,等.呼包盆地周缘壳、幔结构研究[J].地球物理学进展,2009,24(5):1 609-1 615.
[45]王新胜,方剑,许厚泽,等.华北克拉通岩石圈三维密度结构[J].地球物理学报,2012,55(4):1 154-1 160.
[46]酆少英,刘保金,姬计法,等.呼和浩特——包头盆地岩石圈细结构的深地震反射探测[J].地球物理学报,2015,58(4):1 158-1 168.
[47]李志伟,郝天珧,徐亚.华北克拉通上地幔顶部构造特征:来自台站间Pn波到时差成像的约束[J].科学通报,2011,56(12):962-970.
[48]Wessel P,Smith W H F.New improved version of Generic Mapping Tools released[J].EOS,Transactions,American Geophysical Union,1995,79(47):579.