SEISMOLOGY AND GEOLOGY ›› 2011, Vol. 33 ›› Issue (3): 506-524.DOI: 10.3969/j.issn.0253-4967.2011.03.002

• Brief Report • Previous Articles     Next Articles

NEW EVIDENCE FOR THE DISTRIBUTION OF SURFACE RUPTURE ZONE OF THE 1976 MS 7.8 TANGSHAN EARTHQUAKE

GUO Hui, JIANG Wa-li, XIE Xin-sheng   

  1. Institute of Crustal Dynamics,China Earthquake Administration,Beijing 100085,China
  • Received:2011-02-15 Revised:2011-05-22 Online:2011-09-29 Published:2011-12-16

对1976年河北唐山MS7.8地震地表破裂带展布及位移特征的新认识

郭慧, 江娃利, 谢新生   

  1. 中国地震局地壳应力研究所, 北京 100085
  • 作者简介:郭慧,女,1985年生,2011年在中国地震局地壳应力研究所获得固体地球物理学专业硕士学位,研究实习员,现主要从事活动构造研究,电话:15101022544,E-mail:huifeiyang@163.com。
  • 基金资助:

    中国地震局地壳应力研究所基本科研业务专项(ZDJ2007-1)资助。

Abstract:

After the occurrence of the 1976 MS7.8 Tangshan earthquake,some data reported that the surface rupture zone was 8 to 11km long to the south of Tangshan city.The rupture zone was composed by more than ten NE-trending right-lateral strike-slip left-stepping en echelon ruptures,with a general strike of N30°E and a maximum displacement of 1.5~2.3m and a vertical displacement of 0.2~0.7m in most sections.Recently other scholars proposed the surface ruptures appeared in a larger area.An effective way for identifying the tectonic property of the surface ruptures is to use geological method to reveal the distribution and displacement of the strata on the two sides of the surface ruptures.Based on the previous studies and field survey data,we carried out composite borehole profile studies at three sites and trenching at one site across the surface rupture zone of the Tangshan earthquake in a range of 31km to the south of Tangshan city.The three borehole profiles are 4km and 27.5km apart from one another.The total number of boreholes in the three profiles is 28,and the total drilling footage is 1217m.The ages of 51 samples from three borehole profiles have been measured,including seven 14C samples.The drilling investigations on the 3 profiles revealed offset phenomena at the depths of 20~60m beneath the ground surface.The strata consist of sediments of alluvial-proluvial plain,dominated by clay and silty sand,and of littoral plain,dominated by muddy clay and silt.Those offset phenomena show that the displacement amount of stratum increased as multiples of a single displacement with increasing depth.The trenching data verified the fault which was revealed by the drillings.Based on the above,we proved that the surface rupture zone of the 1976 earthquake extends to Xihe in Fengnan County and its total length reaches more than 47km.The 1976 Tangshan earthquake is the newest activity of the Tangshan Fault that had multi-stage activities in the Late Quaternary.The displacement feature of the surface rupture zone is that the north branch is mainly of right-lateral strike-slip motion,and the vertical displacement of the surface is up on the west and down on the east,on the other hand,the vertical displacement on the south branch is up on the east and down on the west,accompanied by some right-lateral slip.Such a faulting style cannot be explained by the movement of a single reverse or normal fault,but is consistent with the vertical displacement field induced by the right-lateral strike-slip of the fault belt.The distribution and rupture style of the newly found surface rupture zone are consistent with the vertical and horizontal displacement field of the Tangshan earthquake.In addition,in the light of the geological structure sections of this area,we discussed the relationship between seismogenic structure of Tangshan earthquake and geological structure,and proposed the suggestions about the next work.

Key words: surface rupture zone, borehole, trench, Tangshan earthquake, seismogenic structure

摘要:

1976年河北唐山MS 7.8地震发生之后,诸多资料报道了唐山市南侧展布的长8~11km的地震地表破裂带。该地表破裂带由10余条NE方向、具右旋走滑特征的地表破裂呈左阶形式组成,总体走向N30°E,最大右旋位移2.3m,多数地段的垂直位移为0.5~0.7m。近年有学者提出,在更大范围内出现的地表破坏现象。分辨这些地表破坏现象构造属性的有效途径是,采用地质学的方法揭示地表破裂两侧的地层分布及其位移特征。在分析前人资料和对唐山地震地表破裂遗迹开展调查的基础上,在唐山市南侧31km范围内,选择3个具有唐山地震地表破裂现象的地点实施了钻孔联合剖面探测,并在其中一个地点实施了开挖探槽。这3条钻孔测线相距4km及27.5km,共钻孔28个,总进尺1 217m,采集了51个地层样品进行年代测试,其中包含7个14C测年样品。调查结果表明,这3条钻孔测线揭示出,地表之下20~60m冲积平原黏土和粉细砂地层与滨海平原淤泥质黏土和粉砂互层的地层断错现象。这些地层的断错特征是随着深度加大地层断错量值呈现单次位移量的倍数增加。孙家楼探槽开挖证实了孙家楼钻孔揭示的断层存在。由此表明1976年唐山MS 7.8地震的地表破裂带向南可延伸至丰南县西河以南,总长度>47km。这次大地震是晚第四纪曾发生多期位移事件的唐山断裂带的最新活动。该地震地表破裂带的位移特征是北段以右旋走滑为主,兼有西升东降垂直位移; 南段以东升西降的倾滑活动为主,兼有右旋走滑活动。这种位移特征不能单独用断层的逆冲或正倾滑活动给予解释,而是断裂带右旋走滑位移场的体现。将该项研究获得的唐山地震地表破裂带的展布及活动方式与唐山地震后依据形变资料展示的唐山地震垂直位移场和水平位移场进行比对,显示了两者之间空间位置及运动方式的吻合。此外,文中根据该地区地质断裂的平面分布及剖面特征,讨论了唐山强震构造与该区地质构造的关系,提出了应进一步开展哪些调查工作的建议。

关键词: 地表破裂带, 钻孔, 探槽, 唐山地震, 发震构造

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