Drilling revealsthe Late Quaternary activity of the Liaocheng-Lancao fault: Discussion on the seismogenicmechanism of the 1937 Heze M7.0 earthquake
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摘要: 华北平原是中国人口最多、经济最为发达的地区之一,也是受地震灾害最为严重的地区。对于该地区断裂活动性和大地震发震机制的研究有利于探索板内地震的发震规律、减轻地震灾害所造成的损失。聊城-兰考断裂是华北平原中南部的一条重要的隐伏的深大断裂。通过浅层地震勘探、钻探与第四纪测年方法相结合的方式,对聊城-聊考断裂的活动性进行精细的研究。坝城寺钻孔揭示了聊城-兰考断裂南段错断了全新统底界,为全新世早期活动断裂,揭露了该断裂晚更新世以来4次古地震事件,单次事件的垂直位错为1.2±0.2-3.7±0.2m。根据钻孔中地层落差,计算该断裂晚更新早期的平均垂直滑动速率约为(0.1±0.05)mm/a,晚更新世晚期-全新世中期的平均滑动速率为(0.35±0.04)mm/a。根据1937年菏泽7.0级和6级地震等震线和地表破裂的分布,认为小留-解元集断裂和东明-成武断裂为该地震的发震断裂。聊城-兰考断裂对于该地区应力的积累、地震的发生有着很好的控制和约束作用,为该次地震的控震构造。
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关键词:
- 华北平原 /
- 聊城-兰考断裂 /
- 浅层地震探测剖面 /
- 钻孔联合剖面 /
- 1937年菏泽M7.0地震
Abstract: The North China Plain (NCP) is one of the most populated and economically developed areas in China, and is a region with high level of seismic hazards. Study on the Quaternary activity of the faults and the seismogenic mechanism of the large earthquakes in NCP is conducive to exploring the seismogenic pattern of intraplate earthquakes and reducing the damage caused by seismic hazards.The Liaocheng-Lancao fault is an important buried deep major fault in the south-central part of the NCP. In this study, the activity of the Liaocheng-Liaocao fault is finely studied by combining shallow seismic exploration, drilling and Quaternary dating methods.The Bachengsi drilling reveals that the southern segment of the Liaocheng-Lancao fault displaces the bottom boundary of the Holocene and is an early Holocene active fault. It also reveals four paleoseismic events since the Late Pleistocene, with vertical displacement of 1.2±0.2-3.7±0.2 m for a single event. Based on the stratigraphic offsets in the boreholes, the average vertical slip rate of this fault is calculated to be about (0.1±0.05) mm/a for the early Late Pleistocene and (0.35±0.04) mm/a for the late Late Pleistocene-middle Holocene. Based on the distribution of isoseismic lines and surface ruptures of the 1937 Heze M 7.0 and M 6 earthquakes, the Xiaoliu-Xieyuanji fault and the Dongming-Chengwu fault are considered to be the seismogenic faults. The Liaocheng-Lancao fault has a good controlling and restraining effect on the accumulation of stress and the occurrence of earthquakes in the area, and is the seismic controlling fault of this earthquake.
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