2014年云南鲁甸M_S6.5地震早期余震序列遗漏地震检测与衰减特征分析

Missing earthquakes detection and temporal decay characteristics analysis of the aftershock sequence of the 2014 Ludian,Yunan,M_S 6.5 earthquake

本文对2014年8月3日云南鲁甸6.5级地震早期余震序列中因波形叠加而遗漏的地震进行了检测,并基于修正的大森公式对序列时间域衰减特征进行了分析.首先利用巧家台连续地震记录波形的高频包络差检测主震发震至当日24点约7.5小时内目录遗漏的地震事件.检测到目录遗漏的ML2.0以上地震159个,最大震级为ML4.2,其中ML4.0以上遗漏地震1个,ML3.0以上遗漏地震3个.主震后1000秒内检测到遗漏地震37个,约为目录给出余震数量的1.76倍.使用补充遗漏地震的目录,基于修正的大森公式拟合主震后10天余震频度随时间的变化.增补遗漏地震后拟合p值由0.85上升至0.99,c值和K值无明显变化,表明鲁甸地震早期余震序列衰减速率高于仅依靠目录得到的结果.遗漏地震检测对于估计早期余震序列衰减速率估计影响较大,早期余震的缺失易造成序列衰减速度的低估.

In this paper we detected missing earthquakes of early aftershock sequence of the Ludian MS 6.5earthquake occurred in August 3rd,2014,and then analyzed the temporal decay characteristics of the sequence based on the modified Omori law.We first detected missing earthquakes in the period of time from origin time of the mainshock to 24：00using the high frequency envelope difference of continuous waveform recording of the station QIJ.By the detection we found 159 missing earthquakes of which the largest magnitude is ML4.2,where 1 missing earthquakes is larger than ML4.0and 3are larger than ML3.0.In 1000 seconds after the mainshock we detected 37 missing earthquakes,which is about 1.76 time more than the number in the catalog.And then we fitted seismic frequency using modified Omori law based on the new catalog which missing earthquakes added.The fitting result of p value is 0.99 compared with 0.85 based on the catalog no missing earthquake added,and the c value and K value are not changed obviously.The result shows that the decay rate of early aftershock sequence of Ludian earthquake maybe higher than the result obtained from the catalog.Missing earthquake detection has greater influence on decay rate estimation of early aftershock sequence,the lack of early aftershocks is easily to cause underestimation to decay rate.