针对九寨沟M_S7.0地震之后不同时间段的余震序列目录，利用推定最大余震震级，给出了实际最大余震震级的估计值。结果表明，推定最大余震震级随主震后时间尺度的延长而趋于稳定，且该值与实际发生的最大余震的震级一致。需要强调的是，就九寨沟地震序列而言，当余震数据较为完备时，采用主震后较短时间段内（1～2天）的余震目录就可以较准确地估算出主震区域内可能发生的最大余震震级。实际上，主震后12h（0.5天）的余震数据已完全可以给出最大余震震级的有效下限。此外，计算中我们采用了里氏震级M_L和面波震级M_S的余震目录，结果显示，2种震级类型目录的估算结果完全一致，表明利用推定最大余震震级估算实际最大余震震级的方法不受震级类型的影响。据此，该最大余震震级快速评估方法可进一步推广应用于我国大陆地区中强震后强余震灾害分析评估中。目前的拟合技术也显示出随着测震技术的不断进步以及余震识别能力的提高，快速评估方法可以在主震后短时间（<1天）内准确地预测可能发生的最大余震震级。

Using the equation for magnitude of the inferred largest aftershock proposed by Shcherbakov and Turcotte(2004), we estimate the magnitude of the largest aftershock following the Jiuzhaigu earthquake from catalogues with different time intervals after the mainshock. The results show that the estimation trends to be a certain value when time intervals become larger and this value is consistent with the magnitude of the real largest aftershock. It should be emphasized that if the aftershock data are relatively complete, using the data in short time intervals after the mainshock(1 day or 2 days)can give an accurate estimation of magnitude of the largest aftershock of the Jiuzhaigu earthquake catalogue. In fact, estimations with different time intervals after the mainshock also indicate that using the aftershock data measured 12 hours(0.5 days)after mainshock can give a rational lower bound of magnitude of the largest aftershock. Moreover, we use two types of aftershock catalogues following the Jiuzhaigu earthquake with Richter magnitude(M_L)and surface-wave magnitude(M_S). And the corresponding results show that the two different catalogues give consistent results which indicates that magnitude of the inferred largest aftershock doesn't depend on types of magnitude chosen for catalogues. Therefore, the method we proposed can be generalized and applied to seismic hazard analysis in southwesten China. Current fitting method also implies that with the help of advance in earthquake detection and aftershocks identification, the method we proposed can accurately predict the magnitude of the largest aftershock in a short time after mainshock. In a word, although we can't predict precisely when and where the largest aftershock will occur, the method we proposed can provide rational magnitude estimation for the largest aftershock in a short period after the mainshock.

P315.9

国家国际科技合作专项（2015DFA21260）资助