Abstract: The Xiadian fault is one of the most important concealed active faults in the northern part of the North China Plain. The Sanhe-Pinggu earthquake (M=8) is the latest surface rupturing event on this fault. Two stratigraphic drill logs on both sides of the Xiadian fault are chronologized by using thermoluminescene and ¹⁴C dating methods. Comparison shows a differential sedimentation on both sides of the fault in the last 26 ka B.P. The stratigraphic marks are established for identifying paleoearthquakes in the drill logs and 11 events are recognized. The main results of this study include: (1)The vertical slip of the Xiadian fault decreased since the Last Glacial Maximum in the past 26ka B.P. The vertical slip rate reached 1.2mm/a during the period of 21～26 ka B.P., 0.98mm/a during the period of 10～21 ka and 0.34mm/a in the past 10 ka B.P., respectively. (2)11 paleoearthquakes are identified by the drill logs which indicate an irregular recurrence behaviour in the past 26ka B.P. The paleoearthquakes clustered with a relatively short interval of 900～1 200 years in the Last Inter-Stadial and Last Glacial Maximum (19.3～26 ka B.P.), while several paleoearthquakes recurred quasi-periodically with an interval of 3 770～5 800 years in the Post Glacial. (3)The paleoearthquake recurrence pattern seems to be associated with paleo-climate variation in the Last Glacial. The earthquake clustering occurred in the Last Inter-Stadial and Last Glacial Maximum with a short recurrence interval. The recurrence interval became longer in the Post Glacial.

Key words: Paleoearthquake, Drill, Stratigraphic section, Surface rupture, North China

摘要： 本文介绍了利用钻孔构造地层学和年代学资料鉴定平原区隐伏活动断裂长期活动习性的一种新的方法和应用实例。通过夏垫断裂上下盘东柳河屯1,2号钻孔地层剖面年代学的测定和岩性的分析与对比,定量地恢复了距今26ka以来断裂上下盘的差异沉积历史和垂直错动过程,建立了鉴别古地震的构造地层学标志。在此基础上,将断裂两侧的累积垂直位移量作为定量约束条件从新到老恢复到每一次地表破裂型地震错动前的状态(扣除后期的同震垂直位移量),可识别出11次地表破裂型古地震事件。指出夏垫断裂上的地表破裂型地震复发行为与古气候环境之间存在着密切的相关关系,气候极度寒冷的末次冰期间亚冰期和鼎盛期(距今19.3～26ka)共发生6次地表破裂型古地震事件,这一时期是夏垫断裂地表破裂型(古)地震丛状群集期,复发间隔介于900～1900a,且多数仅900～1200a。末次冰期鼎盛期晚期到冰后期(距今0～19.3ka)的地表破裂型(古)地震服从准周期复发模式,复发间隔明显地增长,包括公元1679年三河-平谷8级地震在内的最近5次地表破裂型(古)地震的复发间隔介于3700～5800a。

关键词: 古地震, 钻孔, 地层剖面, 地表破裂, 华北