白龙江中游凤安山滑坡26Al暴露年代研究

摘要

Knowledge about the formation age and reactivation times of paleo-landslide are critical for landslide hazard assessment and management.With the development of AMS technology,cosmogenic nuclide dating method has been effectively applied in determining the formation age of paleo-landslide.In this study,the Feng'anshan landslide,which is located at the middle reaches of Bailong River in Southeast Gansu Province,was taken as the study target.Two rock samples,Fas-2 and Fas-1,were obtained from the landslide scarp and a block below the scarp respectively.Considering the masking factors and erosion rate of the sampling site,we calculated the 26Al age of the landslide by using the method of 26Al exposure dating with the cosmic nuclide.The main conclusions are as follows:(1) Two landslide events occurred at about 0.72 ～ 0.75 ka and 2.26 ～ 2.65 ka respectively.The latter formation age corresponds to the documented year of 186 BC in historical descriptions,when earthquakes induced the landslide.(2) The erosion rate has more impact on the dating results of samples with old ages.%准确地重建滑坡发生年代和复活期次是滑坡灾害风险评估与管理的关键步骤之一.近年来,随着AMS技术的发展,宇宙成因核素测年逐渐成为滑坡年代测定的有效手段之一.以甘肃省东南部白龙江中游的凤安山滑坡作为研究对象,在该滑坡后壁和其下方的大石块上各采集了1个宇生核素暴露年代样品,在综合考虑了遮蔽因子以及对该区域的侵蚀速率估算的基础上,研究了该滑坡的宇生核素26 A1暴露年代.结果显示:该滑坡分别大约在0.72～0.75 ka和2.26 ～2.65 ka左右发生过,后者发生时间与该区公元前186年的地震型滑坡发生时间一致;对于年代越老的样品,侵蚀速率对宇生核素测年的年代结果影响越大.