华北盆地北缘宝坻断裂晚更新世以来的活动性研究

通过人工浅层地震反射剖面发现，在香河县荆庄地区，宝坻断裂表现为一条近EW走向的南倾正断层，剖面上呈铲状，对第四系沉积具有一定的控制作用，为一条第四纪活动断裂。通过部署在断层两侧的构造观察孔岩芯对比及¹⁴C测年、光释光测年数据可知，宝坻断裂上断点距地表5~7 m左右，主要活动时间为晚更新世，全新世及中更新世晚期无明显活动。岩芯对比表明，距今10万年以来，宝坻断裂共发生2次地震活动，累积位移2.6 m，其中最近一次地震发生于22 740±70 a BP，同震位移1.4 m；另一次地震发生于距今97.1±4.4~98.0±5.3 ka之间，同震位移1.2 m。根据本次钻孔结果，结合前人对张家口-渤海构造带东段断裂活动性及发震规律的研究，判断宝坻断裂全新世以来整体处于不活跃状态，诱发中强地震和大地震的可能性较低。此外，香河县荆庄一带发育的地裂缝为受宝坻断裂控制的构造型地裂缝，断裂南北两侧的不均匀地面沉降产生的剪切应力会加速荆庄地裂缝的发展。

Study on the Activity of Baodi Fault Since Late Pleistocene in the Northern Margin of North China Basin

Based on the artificial shallow seismic reflection profile, we find that the Baodi fault in Jingzhuang area of Xianghe county is a nearly EW trending normal fault with a spade-shaped profile. It is an active Quaternary fault and controls the deposition of Quaternary. Judging from the comparison of structural observation drilling cores on both sides of the fault and the data of ¹⁴C dating and OSL dating, the up-breakpoint of Baodi fault is about 5-7 m away from the surface, its main activity occurred in Late Pleistocene, and there is no obvious activity in Holocene and late Middle Pleistocene. The comparison of the cores shows that in the last 100 000 years, the Baodi fault has been seismically active twice, with a cumulative displacement of 2.6 m. The recent earthquake occurred at 22 740±70 a BP with a co-seismic displacement of 1.4 m; the other earthquake occurred between 97.1±4.4 ka and 98.0±5.3 ka with a co-seismic displacement of 1.2 m. According to the drilling research, combined with previous research results on fault activity and seismogenic laws in the eastern section of Zhangjiakou-Bohai tectonic belt, we conclude that the Baodi fault has been inactive since Holocene, and the possibility of inducing moderate and large earthquakes is low. In addition, the Jingzhuang ground fissures in Xianghe county are structural ground fissures controlled by the Baodi fault. The shearing stress caused by the uneven ground subsidence on both sides of the Baodi fault also accelerates the development of the Jingzhuang ground fissures.