CRUSTAL STRUCTURES AND TECTONICS OF TANGSHAN EARTHQUAKE AREA: RESULTS FROM DEEP SEISMIC REFLECTION PROFILING

doi:10.3969/j.issn.0253-4967.2011.04.014

Abstract

Abstract:

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.

Key words: Tangshan earthquake area, deep seismic reflection profiling, fine crustal structure, flower-shaped structure, deep-shallow tectonic relations

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。

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

CLC Number:

P631

LIU Bao-jin, QU Guo-sheng, SUN Ming-xin, LIU Kang, ZHAO Cheng-bin, XU Xi-wei, FENG Shao-ying, KOU Kun-peng. CRUSTAL STRUCTURES AND TECTONICS OF TANGSHAN EARTHQUAKE AREA: RESULTS FROM DEEP SEISMIC REFLECTION PROFILING[J]. SEISMOLOGY AND GEOLOGY, 2011, 33(4): 901-912.

刘保金, 曲国胜, 孙铭心, 刘亢, 赵成彬, 徐锡伟, 酆少英, 寇昆朋. 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(4): 901-912.

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