沉积速率摇摆匹配法限定古地震事件日历年龄

THE CALENDAR DATE OF PALEO-EARTHQUAKE EVENT ESTIMATED BY DEPTH-AGE WIGGLE MATCH

尝试运用沉积速率摇摆匹配方法来获得淤泥质泥炭系列样品的日历年龄,并与单个14C年代、时序已知系列14C年代的日历年龄进行对比。结果表明:在采样厚度较小的情况下,沉积速率摇摆匹配方法可以获得较小的日历年龄区间,具有一定的优越性;在采样数量足够多的情况下,系列14C年代贝叶斯校正也可以获得理想的日历年龄区间。综合不同方法获得的结果,推测发生在海原断裂带石卡关沟的古地震事件最大概率日历年龄区间为1 340～1 114calaBP(2σ)。

This paper presents a comparison of the calendar range of individual paleoearthquake calculated by conventional calibration,Bayesian analysis of series of peat samples as well as depth-age wiggle matching.The results suggest that：（1）The Bayesian analysis provides an excellent means to enhance chronological resolution when applied to a series of radiocarbon dates from sections with clear stratigraphic relationships.Such application can assess systematic errors when combined with independent chronological information,and determine the optimum chronological information for specific events and contexts.（2）The calendar ranges of series of samples collected from the same peat but different sampling thickness were compared with that of depth-age wiggle matching.The result shows that the chronological resolution by depth-age wiggle matching for the peat sample with thickness less than 2cm could achieve less than 100a.Therefore,the condition to obtain a high resolution calendar age is to have 5～6 samples with 0.5～2cm sampling thickness each and the interval of samples is 0.5～1cm.（3）The calendar range of paleoearthquakes constrained by the Markov chain Monte Carlo（MCMC）Bayesian analysis model,which constructs the order of samples according to their position in the strata with series of radiocarbon dates,was compared with calendar range by the conventional method.The results show that Bayesian analysis could obtain high-precision calendar dates for closely spaced samples.（4）Therefore,the calendar interval of the paleoearthquake event on the middle segment of Huaiyuan Fault was inferred as 1340～1114cal aBP（2σ）by the above systematical comparsion.