山东郯城麦坡中更新世地震事件记录*

山东郯城麦坡被命名为典型地震活动断层遗址,其最醒目的标志是郯庐断裂带主干断层(F₂)东盘的紫灰色下白垩统逆冲到断层西盘的红棕色第四系之上且界线截然。野外调查和试验分析表明,郯城麦坡第四系于泉组中发育液化砂涌管、液化砂脉、震裂缝充填构造和同沉积断层等地震引发的软沉积物变形构造——地震事件记录。根据软沉积物变形构造的砂质黏土光释光测年分析,推断这些软沉积物变形构造所记录的地震事件属郯庐断裂带主干断层F₂在中更新世晚期发生的强构造与地震活动。这些地震事件记录为研究郯庐断裂带新构造运动与地震活动提供了新资料,也丰富了该地震活动断层遗址的内涵。

Records of the Pleistocene seismic events in Tancheng Maipo,Shandong Province

Tancheng Maipo is named as a typical site of the seismic active fault,in which the most eye-catching sign is that the purple-gray Lower Cretaceous of the east-wall thrust up to the red-brown Quaternary of the west-wall of the second trunk fault(F₂)of Tanlu Fault Zone,and the boundary is very clear. The field investigation and the test analysis showed that some earthquake-induced soft sediment deformation structures developed in the Quaternary Yuquan Formation of Tancheng Maipo,including liquefied sand flow pipes,liquefied sand veins,seismic fissure-filling structures,syn-sedimentary faults and other deformation, which were seismic event records. According to the OSL analysis of sandy clay in the soft sediment deformation structures,it is affirmed that the seismic events recorded by these soft sediment deformation structures should belong to strong tectonic seismic activities of the second trunk fault F₂ during the late stage of the Mid-Pleistocene in Tanlu Fault Zone. These seismic event records not only provide new data for new tectonic movements and seismic activities in the Tanlu Fault Zone,but also enrich geoscience connotations of the seismic active fault site.