红河断裂带中段北探槽古地震及其标志性地层佐证  

Paleoearthquakes and the symbolic stratum proof in the trenches of the northern part in the middle segment of the Red River Fault Zone

作　　者：郭君 李西 张彦琪[3] GUO Jun;LI Xi;ZHANG Yanqi(City College,Kunming University of Science and Technology,Kunming 650051,Yunnan;School of Earth Science,Yunnan University,Kunming 650500,Yunnan;Yunnan Earthquake Administration,Kunming 650224,Yunnan)

机构地区：[1]昆明理工大学城市学院,云南昆明650051 [2]云南大学地球科学学院,云南昆明650500 [3]云南省地震局,云南昆明650201

出　　处：《第四纪研究》2021年第6期1532-1545,共14页Quaternary Sciences

基　　金：中国地震局星火计划攻关项目(批准号:XH19040和XH13021);中国地震局预测研究所基本科研业务专项重点项目(批准号:2017IES010204)共同资助。

摘　　要：探槽方法能够揭露地质记录中保存的古地震事件,可弥补仪器地震及历史地震记录的短暂性及局限性。文章通过数字影像分析、地质地貌调查,在红河断裂带中段北变形遗迹保存较好的德苴乡大丫口村段开挖了一个大型组合探槽。根据探槽剖面揭露的断裂信息以及断裂切、盖地层关系分析,组合探槽共揭露出了3次古地震事件,从老到新命名为E1、E2和E3。利用OxCal软件对古地震事件断错地层及覆盖地层中的炭屑样品AMS^(14)C测年结果进行校正分析,3次古地震事件分别限定在约1190 BC、341~126 BC和1460~1784 A.D.,最新一次事件E3应对应1652年弥渡M7地震。其中年龄限定较好的两次事件E2、E3的复发间隔约1800~2000 a表明,红河断裂中段北具有复发周期较长的特征。基于铁锰结核很可能是历史上新构造运动地质作用下,土壤环境巨大波动条件下形成的认识,以及组合探槽中揭露的标志性地层——铁锰结核层中多个炭屑样品年龄均为全新世,进一步佐证了红河断裂中段北在全新世期间曾有过多次强地震活动。Trench works can reveal paleoearthquakes preserved in the geological record,and make up for the shortness and limitation of the instrumental earthquake and historical earthquake records.Based on digital image analysis and field investigation,one large combined trenches have been opened in Dayakou Village,Deju Township,where the remains of tectonic deformations are well preserved in the north of the middle segment along the Red River Fault Zone(RRFZ).Three paleoearthquakes have been revealed in the multiple trenches,which are named E1,E2 and E3 from the oldest to the youngest.These events E1,E2 and E3 were constrained in ca.1190 BC,341~126 BC and 1460~1784 A.D.,respectively,on base of analyzing the AMS^(14)C dating results of charcoal samples in the faulted and covered layers by the OxCal software.We associate the youngest event E3 with 1652 M7 earthquake,which happened in Midu County,Yunnan Province,China.The recurrence interval of E2 and E3 is about 1800~2000 a,which shows the characteristic of longer recurrence interval of the northern part in the middle segment of RRFZ.Based on the recognition that the iron-manganese nodules are likely to be formed under the geological action of the neotectonics in history and the huge fluctuations of the soil environment.Furthermore,several Holocene dating ages of the charcoal samples in the symbolic iron-manganese nodules layers in the multiple trenches,which further proves that there are several strong earthquakes in the north of the middle segment of RRFZ during the Holocene.

关 键 词：红河断裂带 组合探槽 古地震 AMS^(14)C测年 复发间隔 铁锰结核层 

分 类 号：P315.2[天文地球—地震学] P542[天文地球—固体地球物理学]