唐山地震区地壳结构和构造:深地震反射剖面结果
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摘要
1976年7月28日,在唐山地区发生了7.8级大地震。为了研究该区的地壳结构和断裂的深浅构造关系,2009年,我们在唐山市南部的丰南地区,跨唐山断裂带完成了1条道间距40m、炮间距200m、50次覆盖的深地震反射探测剖面。结果表明:研究区的地壳厚度为32～34km,莫霍面自东向西逐渐加深,在丰南县和宣庄镇之间,中-下地壳反射和壳幔过渡带反射均被唐山深断裂错开,断裂两侧的莫霍面发生错断,显示出唐山深断裂的走滑作用。反射剖面揭示的唐山断裂带是一条规模较大的陆内走滑断裂,浅部表现为典型的花状构造,在深部切割和扰动了下地壳物质和壳幔过渡带。这种深、浅共存的断裂构造体系是控制该区地震孕育和发生的重要因素,也是唐山地震区的深、浅构造背景。
On July 28,1976,the great Tangshan earthquake(M7.8)occurred in the Tangshan area of Hebei Province,which shocked the whole world.Before this earthquake,there was no earthquake with magnitude over M7.0 in this area.After this earthquake,the crustal structures and tectonics around Tangshan earthquake area remain unclear.In order to investigate the fine crustal structures,the main fault geometries and the relations between the deep-shallow tectonics in this area,a deep seismic reflection profiling with 40m receiver spacing and 200m shot spacing as well as 60-fold across the Tangshan Fault zone was carried out in the Fengnan region of Tangshan in 2009.Because our results have much higher spatial resolution than that of previous results of deep geophysical prospecting,some new features of the crustal structures and fault tectonics were revealed by this study.The results show that the thickness of the crust is about 32～34km along the profile,the Moho gradually deepens from east to west.Between Fengnan county and Xuanzhuang town,the reflections in the middle-lower crust and crust-mantle transitional zone are staggered by the deep Tangshan Fault,and dislocation occurs on the Moho on both sides of the deep fault,indicating the strike-slip effect of the deep Tangshan Fault.Tangshan Fault belt revealed by deep seismic reflection profile is a huge intra-continental strike-slip fault,and its shallow part appears as a typical flower-shaped structure,incising and disturbing the lower crust and crust-mantle transitional zone in the deep part.The complex faults and structures coexisting in both deep and shallow parts of the crust are the tectonic background for the Tangshan Earthquake,and also an important factor controlling the earthquake activity in the area.Tangshan earthquake area,deep seismic reflection profiling,fine crustal structure,flower-shaped structure,deep-shallow tectonic relations DEEP STRUCTURE IN SHIJIAZHUANG AND THE VICINITY BY MAGNETOTELLURICS ZHAN YanZHAO Guo-zeWANG Li-fengWANG Ji-junXIAO Qi-bin(Institute of Geology,China Earthquake Administration,Beijing100029,China) The Shijiazhuang City in Hebei Province lies at the junction between the Taihangshan uplift in the west and the Jizhong depression of North China in the east,abutting the front-range fault zone of the Taihangshan in the west.The Xingtai M7.2 earthquake of March 1966 occurred southeast to this area.In October 2010,a broadband magnetelluric(MT)survey was conducted in the Shijiazhuang City and adjacent regions to probe the deep structure.The 167km-long MT profile began from the Niangziguan town,extended southeastward through southern Shijiazhuang City,and terminated at Wangchang town of Jixian county.MT data were collected at 64 sites along this profile.In MT data processing,in addition to the remote reference and robust techniques,the multi-point and multi-frequency tensor decomposition was employed to determine the regional electric strike,and the NLCG 2D inversion was performed on TE and TM data.The result shows that a combination of an east-dipping low-angle normal fault in the shallow subsurface and a steep electric boundary at depth characterizes the deep structure beneath the study area.The electric structures in the shallow crust(above 10km)and deep crust(below 10km)seem to be independent.The Jinxian Fault and Xinhe Fault extend to a depth of less than～7km.High conductivity layer(HCL) is present below the depth of 10km between the front-range fault zone of the Taihangshan and the Xinhe Fault.There is a low resistivity boundary zone below the HCL and it cuts through the Moho.The hypocenter of the 1966 Xingtai Baichikou strong aftershock is located at the linkage between Xinhe Fault and deep electrical boundary,and on its top is a high resistance body and below it is the high conductivity layer(HCL).The HCL and the deep low resistivity boundary zone below the HCL are a channel of deep thermal upwelling and elastic energy migration.The 1966 Xingtai earthquake swarm is closely related to the deep material damping.
On July 28,1976,the great Tangshan earthquake(M7.8)occurred in the Tangshan area of Hebei Province,which shocked the whole world.Before this earthquake,there was no earthquake with magnitude over M7.0 in this area.After this earthquake,the crustal structures and tectonics around Tangshan earthquake area remain unclear.In order to investigate the fine crustal structures,the main fault geometries and the relations between the deep-shallow tectonics in this area,a deep seismic reflection profiling with 40m receiver spacing and 200m shot spacing as well as 60-fold across the Tangshan Fault zone was carried out in the Fengnan region of Tangshan in 2009.Because our results have much higher spatial resolution than that of previous results of deep geophysical prospecting,some new features of the crustal structures and fault tectonics were revealed by this study.The results show that the thickness of the crust is about 32～34km along the profile,the Moho gradually deepens from east to west.Between Fengnan county and Xuanzhuang town,the reflections in the middle-lower crust and crust-mantle transitional zone are staggered by the deep Tangshan Fault,and dislocation occurs on the Moho on both sides of the deep fault,indicating the strike-slip effect of the deep Tangshan Fault.Tangshan Fault belt revealed by deep seismic reflection profile is a huge intra-continental strike-slip fault,and its shallow part appears as a typical flower-shaped structure,incising and disturbing the lower crust and crust-mantle transitional zone in the deep part.The complex faults and structures coexisting in both deep and shallow parts of the crust are the tectonic background for the Tangshan Earthquake,and also an important factor controlling the earthquake activity in the area.Tangshan earthquake area,deep seismic reflection profiling,fine crustal structure,flower-shaped structure,deep-shallow tectonic relations DEEP STRUCTURE IN SHIJIAZHUANG AND THE VICINITY BY MAGNETOTELLURICS ZHAN YanZHAO Guo-zeWANG Li-fengWANG Ji-junXIAO Qi-bin(Institute of Geology,China Earthquake Administration,Beijing100029,China) The Shijiazhuang City in Hebei Province lies at the junction between the Taihangshan uplift in the west and the Jizhong depression of North China in the east,abutting the front-range fault zone of the Taihangshan in the west.The Xingtai M7.2 earthquake of March 1966 occurred southeast to this area.In October 2010,a broadband magnetelluric(MT)survey was conducted in the Shijiazhuang City and adjacent regions to probe the deep structure.The 167km-long MT profile began from the Niangziguan town,extended southeastward through southern Shijiazhuang City,and terminated at Wangchang town of Jixian county.MT data were collected at 64 sites along this profile.In MT data processing,in addition to the remote reference and robust techniques,the multi-point and multi-frequency tensor decomposition was employed to determine the regional electric strike,and the NLCG 2D inversion was performed on TE and TM data.The result shows that a combination of an east-dipping low-angle normal fault in the shallow subsurface and a steep electric boundary at depth characterizes the deep structure beneath the study area.The electric structures in the shallow crust(above 10km)and deep crust(below 10km)seem to be independent.The Jinxian Fault and Xinhe Fault extend to a depth of less than～7km.High conductivity layer(HCL) is present below the depth of 10km between the front-range fault zone of the Taihangshan and the Xinhe Fault.There is a low resistivity boundary zone below the HCL and it cuts through the Moho.The hypocenter of the 1966 Xingtai Baichikou strong aftershock is located at the linkage between Xinhe Fault and deep electrical boundary,and on its top is a high resistance body and below it is the high conductivity layer(HCL).The HCL and the deep low resistivity boundary zone below the HCL are a channel of deep thermal upwelling and elastic energy migration.The 1966 Xingtai earthquake swarm is closely related to the deep material damping.
引文
杜春涛,孟宪梁,陈书贤.1985.唐山地震的地裂缝[A].见:刘恢先主编.唐山大地震震害(一).北京:地震出版社.174—189.DU Chun-tao,MENG Xian-liang,CHEN Shu-xian.1985.Ground fissures caused by Tangshan earthquake[A].In:LIUHui-xian(ed).Disaster of Tangshan Great Earthquake(1).Seismological Press,Beijing.174—189(in Chinese).
桂琨长,耿世昌.1987.值得再三思考的唐山地震构造[J].中国地震,3(增刊):79—84.GUI Kun-chang,GENG Shi-chang.1987.Worthwhile considering the seismo-structure of the Tangshan earthquake[J].Earthquake Research in China,3(suppl):79—84(in Chinese).
虢顺民,李志义,程绍平,等.1977.唐山地震区域构造背景和发震模式的讨论[J].地质科学,4:305—320.GUO Shun-min,LI Zhi-yi,CHENG Shao-ping,et al.1977.A discussion on regional structures and earthquake model inTangshan earthquake area[J].Scientia Geologica Sinica,4:305—320(in Chinese).
国家地震局《一九七六年唐山地震》编辑组.1982.一九七六年唐山地震[M].北京:地震出版社.4—23.Editorial Group of“The1976Tangshan Earthquake”,State Seismological Bureau.1982.The1976Tangshan Earthquake[M].Seismological Press,Beijing.4—23(in Chinese).
李传友,汪一鹏,王志才.2007.中国东部城市地区隐伏断裂上断点与最新活动时代关系的初步分析:以邢台、唐山地震区为例[J].地震地质,29(2):431—445.LI Chuan-you,WANG Yi-peng,WANG Zhi-cai.2007.Some analyses on relation between the upper offset point andlatest activity times of buried faults in cities of eastern China:Taking the Xingtai and Tangshan earthquake regionsas an example[J].Seismology and Geology,29(2):431—445(in Chinese).
李绍炳.1986.唐山地震的发震构造与成因的探讨[J].华北地震科学,4(2):56—62.LI Shao-bing.1986.A discussion of the seismo-tectonics and the cause of Tangshan earthquake[J].North ChinaEarthquake Sciences,4(2):56—62(in Chinese).
刘保金,胡平,孟勇奇,等.2009.北京地区地壳精细结构的深地震反射剖面探测研究[J].地球物理学报,52(9):2264—2272.LIU Bao-jin,HU Ping,MENG Yong-qi,et al.2009.Research on fine crustal structure using deep seismic reflectionprofile in Beijing region[J].Chinese J Geophys,52(9):2264—2272(in Chinese).
刘昌铨,嘉世旭.1986.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,8(4):341—353.LIU Chang-quan,JIA Shi-xu.1986.Structural property of the crust and the upper mantle in the Tangshan earthquakeregion:A method of computing body wave theoretical seismogram and the result of analysis of2-D inhomogeneousmedia[J].Acta Seismologica Sinica,8(4):341—353(in Chinese).
刘启元,王峻,陈九辉,等.2007.1976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,14(6):205—213.LIU Qi-yuan,WANG Jun,CHEN Jiu-hui,et al.2007.Seismogenic tectonic environment of1976great Tangshanearthquake:Results given by dense seismic array observations[J].Earth Science Frontiers,14(6):205—213(inChinese).
陆涵行,曾融生,郭建明,等.1988.唐山震区可控震源深反射剖面结果分析[J].地球物理学报,31(1):27—36.LU Han-xing,ZENG Rong-sheng,GUO Jian-ming,et al.1988.Results from deep seismic reflection profiling inTangshan region[J].Chinese J Geophys,31(1):27—36(in Chinese).
江娃利.2006.有关1976年唐山地震发震断层的讨论[J].地震地质,28(2):312—318.JIANG Wa-li.2006.Discussion on seismogenic fault of the1976Tangshan earthquake[J].Seismology and Geology,28(2):312—318(in Chinese).
邱泽华,马瑾,刘国玺.2005.新发现的唐山地震大断层[J].地震地质,27(4):669—677.QIU Ze-hua,MA Jin,LIU Guo-xi.2005.Discovery of the great fault of the Tangshan earthquake[J].Seismology andGeology,27(4):669—677(in Chinese).
薛志照.1986.唐山地震震源深度分布与地壳结构的关系[J].地震地质,8(3):69—78.XUE Zhi-zhao.1986.The relationship between focal depth and crustal structure for Tangshan earthquake[J].Seismology and Geology,8(3):69—78(in Chinese).
杨宝俊,刘财,杨平华,等.1999.用近垂直地震反射方法研究莫霍面的特征与成因[J].地球物理学报,42(5):617—628.YANG Bao-jun,LIU Cai,YANG Ping-hua,et al.1999.The study of Moho characteristics and formation by nearlyvertical seismic reflection method[J].Chinese J Geophys,42(5):617—628(in Chinese).
尤惠川,徐锡伟,吴建平,等.2002.唐山地震深浅构造关系研究[J].地震地质,24(4):571—582.YOU Hui-chuan,XU Xi-wei,WU Jian-ping,et al.2002.Study on the relationship between shallow and deep structuresin the1976Tangshan earthquake area[J].Seismology and Geology,24(4):571—582(in Chinese).
曾融生,陆涵行,丁志峰.1988.从地震折射和反射剖面结果讨论唐山地震成因[J].地球物理学报,31(4):383—397.ZENG Rong-sheng,LU Han-xing,DING Zhi-feng.1988.A discussion on genesis of the Tangshan earthquake fromseismic refraction and reflection profiling[J].Chinese J Geophys,31(4):383—397(in Chinese).
张先康,王椿镛,刘国栋,等.1996.延庆—怀来地区地壳细结构:利用深地震反射剖面[J].地球物理学报,39(3):356—363.ZHANG Xian-kang,WANG Chun-yong,LIU Guo-dong,et al.1996.Fine crustal structure in Yanqing-Huailai region bydeep seismic reflection profiling[J].Chinese J Geophys,39(3):356—363(in Chinese).
张之立,李钦祖,谷继承,等.1980.唐山地震的破裂过程及其力学分析[J].地震学报,2(2):111—129.ZHANG Zhi-li,LI Qin-zu,GU Ji-cheng,et al.1980.The fracture processes of the Tangshan earthquake and itsmechanical analysis[J].Acta Seimologica Sinica,2(2):111—129(in Chinese).
王椿镛,王贵美,林中洋,等.1993.用深地震反射方法研究邢台地震区地壳细结构[J].地球物理学报,36(4):445—452.WANG Chun-yong,WANG Gui-mei,LIN Zhong-yang,et al.1993.A study on fine crustal structure in Xingtaiearthquake area based on deep seismic reflection profiling[J].Chinese J Geophys,36(4):445—452(inChinese).
王景明,郑文俊,陈国顺,等.1981.唐山地震断面主断裂带及地震成因[J].地震研究,4(4):437—450.WANG Jing-ming,ZHENG Wen-jun,CHEN Guo-shun,et al.1981.A study on the principal surface fracture belt createdby the Tangshan earthquake and the cause of occurrence of the earthquake[J].Journal of SeismologicalResearch,4(4):437—450(in Chinese).
Sandmeier K J,Wenzel F.1986.Synthetic seismograms for a complex crustal model[J].Geophys Res Lett,13:22—25.
桂琨长,耿世昌.1987.值得再三思考的唐山地震构造[J].中国地震,3(增刊):79—84.GUI Kun-chang,GENG Shi-chang.1987.Worthwhile considering the seismo-structure of the Tangshan earthquake[J].Earthquake Research in China,3(suppl):79—84(in Chinese).
虢顺民,李志义,程绍平,等.1977.唐山地震区域构造背景和发震模式的讨论[J].地质科学,4:305—320.GUO Shun-min,LI Zhi-yi,CHENG Shao-ping,et al.1977.A discussion on regional structures and earthquake model inTangshan earthquake area[J].Scientia Geologica Sinica,4:305—320(in Chinese).
国家地震局《一九七六年唐山地震》编辑组.1982.一九七六年唐山地震[M].北京:地震出版社.4—23.Editorial Group of“The1976Tangshan Earthquake”,State Seismological Bureau.1982.The1976Tangshan Earthquake[M].Seismological Press,Beijing.4—23(in Chinese).
李传友,汪一鹏,王志才.2007.中国东部城市地区隐伏断裂上断点与最新活动时代关系的初步分析:以邢台、唐山地震区为例[J].地震地质,29(2):431—445.LI Chuan-you,WANG Yi-peng,WANG Zhi-cai.2007.Some analyses on relation between the upper offset point andlatest activity times of buried faults in cities of eastern China:Taking the Xingtai and Tangshan earthquake regionsas an example[J].Seismology and Geology,29(2):431—445(in Chinese).
李绍炳.1986.唐山地震的发震构造与成因的探讨[J].华北地震科学,4(2):56—62.LI Shao-bing.1986.A discussion of the seismo-tectonics and the cause of Tangshan earthquake[J].North ChinaEarthquake Sciences,4(2):56—62(in Chinese).
刘保金,胡平,孟勇奇,等.2009.北京地区地壳精细结构的深地震反射剖面探测研究[J].地球物理学报,52(9):2264—2272.LIU Bao-jin,HU Ping,MENG Yong-qi,et al.2009.Research on fine crustal structure using deep seismic reflectionprofile in Beijing region[J].Chinese J Geophys,52(9):2264—2272(in Chinese).
刘昌铨,嘉世旭.1986.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,8(4):341—353.LIU Chang-quan,JIA Shi-xu.1986.Structural property of the crust and the upper mantle in the Tangshan earthquakeregion:A method of computing body wave theoretical seismogram and the result of analysis of2-D inhomogeneousmedia[J].Acta Seismologica Sinica,8(4):341—353(in Chinese).
刘启元,王峻,陈九辉,等.2007.1976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,14(6):205—213.LIU Qi-yuan,WANG Jun,CHEN Jiu-hui,et al.2007.Seismogenic tectonic environment of1976great Tangshanearthquake:Results given by dense seismic array observations[J].Earth Science Frontiers,14(6):205—213(inChinese).
陆涵行,曾融生,郭建明,等.1988.唐山震区可控震源深反射剖面结果分析[J].地球物理学报,31(1):27—36.LU Han-xing,ZENG Rong-sheng,GUO Jian-ming,et al.1988.Results from deep seismic reflection profiling inTangshan region[J].Chinese J Geophys,31(1):27—36(in Chinese).
江娃利.2006.有关1976年唐山地震发震断层的讨论[J].地震地质,28(2):312—318.JIANG Wa-li.2006.Discussion on seismogenic fault of the1976Tangshan earthquake[J].Seismology and Geology,28(2):312—318(in Chinese).
邱泽华,马瑾,刘国玺.2005.新发现的唐山地震大断层[J].地震地质,27(4):669—677.QIU Ze-hua,MA Jin,LIU Guo-xi.2005.Discovery of the great fault of the Tangshan earthquake[J].Seismology andGeology,27(4):669—677(in Chinese).
薛志照.1986.唐山地震震源深度分布与地壳结构的关系[J].地震地质,8(3):69—78.XUE Zhi-zhao.1986.The relationship between focal depth and crustal structure for Tangshan earthquake[J].Seismology and Geology,8(3):69—78(in Chinese).
杨宝俊,刘财,杨平华,等.1999.用近垂直地震反射方法研究莫霍面的特征与成因[J].地球物理学报,42(5):617—628.YANG Bao-jun,LIU Cai,YANG Ping-hua,et al.1999.The study of Moho characteristics and formation by nearlyvertical seismic reflection method[J].Chinese J Geophys,42(5):617—628(in Chinese).
尤惠川,徐锡伟,吴建平,等.2002.唐山地震深浅构造关系研究[J].地震地质,24(4):571—582.YOU Hui-chuan,XU Xi-wei,WU Jian-ping,et al.2002.Study on the relationship between shallow and deep structuresin the1976Tangshan earthquake area[J].Seismology and Geology,24(4):571—582(in Chinese).
曾融生,陆涵行,丁志峰.1988.从地震折射和反射剖面结果讨论唐山地震成因[J].地球物理学报,31(4):383—397.ZENG Rong-sheng,LU Han-xing,DING Zhi-feng.1988.A discussion on genesis of the Tangshan earthquake fromseismic refraction and reflection profiling[J].Chinese J Geophys,31(4):383—397(in Chinese).
张先康,王椿镛,刘国栋,等.1996.延庆—怀来地区地壳细结构:利用深地震反射剖面[J].地球物理学报,39(3):356—363.ZHANG Xian-kang,WANG Chun-yong,LIU Guo-dong,et al.1996.Fine crustal structure in Yanqing-Huailai region bydeep seismic reflection profiling[J].Chinese J Geophys,39(3):356—363(in Chinese).
张之立,李钦祖,谷继承,等.1980.唐山地震的破裂过程及其力学分析[J].地震学报,2(2):111—129.ZHANG Zhi-li,LI Qin-zu,GU Ji-cheng,et al.1980.The fracture processes of the Tangshan earthquake and itsmechanical analysis[J].Acta Seimologica Sinica,2(2):111—129(in Chinese).
王椿镛,王贵美,林中洋,等.1993.用深地震反射方法研究邢台地震区地壳细结构[J].地球物理学报,36(4):445—452.WANG Chun-yong,WANG Gui-mei,LIN Zhong-yang,et al.1993.A study on fine crustal structure in Xingtaiearthquake area based on deep seismic reflection profiling[J].Chinese J Geophys,36(4):445—452(inChinese).
王景明,郑文俊,陈国顺,等.1981.唐山地震断面主断裂带及地震成因[J].地震研究,4(4):437—450.WANG Jing-ming,ZHENG Wen-jun,CHEN Guo-shun,et al.1981.A study on the principal surface fracture belt createdby the Tangshan earthquake and the cause of occurrence of the earthquake[J].Journal of SeismologicalResearch,4(4):437—450(in Chinese).
Sandmeier K J,Wenzel F.1986.Synthetic seismograms for a complex crustal model[J].Geophys Res Lett,13:22—25.
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