北京平原区夏垫断裂1679年三河—平谷8级地震地表破裂带特征

Characteristics of Surface Rupture Zone of 1679 Sanhe-Pinggu M 8 Earthquake in Xiadian Fault of Beijing Plain,China

夏垫断裂是北京地区重要的活动断裂之一。1679年该断裂发生三河—平谷8级地震,是北京及邻区历史记录的最大地震,地表形成了至今仍清晰可见的地震地表破裂带。弄清楚该断裂古地震活动和地表破裂带特征是优化北京地区国土空间开发格局和防灾减灾体系建设的重要内容。通过探槽开挖、光释光(OSL)测年、断层陡坎形态及地层位错分析,揭示了夏垫断裂古地震活动性、古地震序列和地表破裂带特征。结果表明:(1)夏垫断裂大胡庄南探槽显示的地层错断、地震楔及崩积楔等揭示了夏垫断裂的两次古地震事件,分别约为(1.610±0.130)ka B.P.古地震及1679年三河—平谷8级地震,地层位错分别约为0.3、2.5 m;(2)夏垫断裂20 ka以来存在7个期次的古地震事件,大地震的平均复发周期约为2716年;(3)地震地表破裂带地层位错整体趋势与地形测量数据所得结果基本一致,但在大康庄段到齐心庄段,地层位错距离大于断层陡坎地面测量的高度,表明地表断层陡坎形态可能受人类活动的影响,探槽揭露的地层位错量有助于进一步理解夏垫断裂1679年三河—平谷8级地震地表破裂带特征。

The Xiadian fault is one of the most important active faults in Beijing.The Sanhe-Pinggu M 8 earthquake,which occurs on the fault in 1679,is the largest earthquake on record in Beijing and its adjacent areas.The surface forms a seismic surface rupture zone that is still clearly visible.The characteristics of the ancient seismic activity and surface rupture zone of the fault are important for optimizing the land-space development pattern and the disaster prevention and mitigation system in Beijing.Through trench excavation,optically stimulated luminescence(OSL)dating,fault scarp morphology and stratigraphic dislocation analysis,the paleoseismic activity,paleoseismic sequence,and surface rupture zone characteristics of Xiadian fault were revealed.The results show that①the stratigraphic dislocations,seismic wedges,and colluvial wedges displayed by Dahuzhuang south trench of Xiadian fault reveal two paleoseismic events,which are about(1.610±0.130)ka B.P.and 1679 Sanhe-Pinggu M 8 earthquake;the stratigraphic dislocations are about 0.3 and 2.5 m,respectively;②there has been seven periods of paleoearthquake events since 20 ka on Xiadian fault,and the average recurrence period of violent earthquakes is about 2716 years;③however,in the Dakangzhuang-Qixinzhuang sections,the stratigraphic dislocation distance is greater than the height of the fault scarp measured on the ground,indicating that the surface fault scarp morphology may be affected by human activities.The amount of stratigraphic dislocation revealed by the trench is helpful to further understand the surface rupture zone characteristics of 1679 Sanhe-Pinggu M 8 earthquake on Xiadian fault.