关键词: 古地震, 钻孔, 地层剖面, 地表破裂, 华北

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