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.
出处
《地震地质》
EI
CSCD
北大核心
2011年第4期901-912,共12页
Seismology and Geology
基金
地震行业科研专项"中国地震活动断层探察-华北构造区"(200908001)
河北省城市活断层试验探测项目共同资助
关键词
唐山地震区
深地震反射剖面
地壳细结构
花状构造
深浅构造关系
the piedmont fault zone of Taihangshan
Jizhong depression
deep electrical structure
high conductivity layer
