2010年青海玉树MS 7.1地震序列E TAS模型参数及其变化特征研究

摘要

采用时间序列的“传染型余震序列”(ETAS)模型和最大似然法对2010年4月14日青海玉树MS 7.1地震序列的参数进行了估计。为考察其结果的稳定性,设定不同的截止震级和不同的拟合截止时间分别进行序列参数估算。选用截止震级MC=ML 1.5对玉树MS 7.1地震序列整体的参数进行拟合,计算获得α=0.9482,p=1.0596和b=0.8173。与中国大陆M>7.0地震序列的平均序列参数相比较表明,玉树MS 7.1地震序列表现为触发次级余震的能力较弱,序列衰减速率较快。研究表明,截止震级MC 对α、k 和p 值有一定的影响。随截止震级逐渐增大,参数k 值逐渐减小,α值总体上有增加的趋势,而对p 值的影响较小。在地震序列的早期阶段,ETAS 模型参数中的p值和α值在震后14天内随时间的变化幅度较为明显,其后各参数变化相对平稳。%The maximum likelihood method is used and the epidemic-type aftershock sequence (ETAS)model is fitted in the analysis of aftershock sequence characteristics of the April 14,2010 Yushu (MS7.1)earthquake that occurred in Qinghai province.To examine parameter stability, ETAS parameters and their standard errors are estimated with different cutoff magnitudes,MC , and different ending times for the fitting interval.The overall parameters are observed to beα=0.948 2,p=1.059 6,and b=0.817 3 with setting MC=ML1.5.Compared to other M>7.0 earth-quake sequences on the continental China,the Yushu MS7.1 earthquake sequence is characterized by a weak triggering capability in generating secondary aftershocks,and a quick decay rate of aftershocks.A systematic approach for using multiple cutoff magnitudes above the magnitude of completeness is adopted in the calculation process to examine stability of the sequence parameters and to analyze the degree to which they are affected.The cutoff magnitude,MC ,is observed to have a certain effect on the value ofα,k,and p (with an increase in MC the value of k decreases, there is a general increasing trend ofα,but less influence on p ).ETAS model parameters with different sequence durations are studied in this paper,together with their temporal variations and stability in the early stage after the shock.There is variation in the range of p andαshortly after the earthquake stops for different cutoff magnitudes within the same earthquake,whereas there is a trend of p andαis towards convergence and stability after stabilization of seismic activity. Furthermore,there is evident change in the temporal variation of ETAS parameters 14 days after the mainshock,when the parameters become relatively stable.