2013年芦山MS7.0地震序列参数的早期 特征: 传染型余震序列模型计算结果

为考察2013年4月20日芦山M_S7.0地震震后序列参数的早期特征， 利用“传染型余震序列”(ETAS)模型和最大似然法进行了参数估计. 设定截止震级M_c=M_L2.0， 拟合时段为震后0.31—24.12天， 计算获得α=1.89， p=1.22， 同时利用最大似然法估计获得b=0.72. 与中国大陆地区其它中强震的余震序列参数的比较表明， 芦山M_S7.0地震序列参数表现为触发次级余震的能力较弱和序列衰减速率较快的特征， 反映出余震区相对较高的应力水平. 为检测结果的稳定性， 设定不同的截止震级M_c以及不同的拟合截止时间， 分别进行参数拟合和参数标准差估计. 结果表明， M_c的选取对α值影响明显， 对p值影响则较小. 此外， 震后10天内获得的参数拟合结果随时间变化较为明显， 而其后各参数变化总体较为平稳. 

Statistical analysis of ETAS parameters in the early stage of the 2013 Lushan Ms7.0 earthquake sequence

The epidemic-type aftershock sequence (ETAS) model was fitted to the aftershock sequence of the April 20, 2013 Lushan M_S7.0 earthquake with cutoff magnitude M_c=M_L2.0 and a fitting time interval from 0.31 days to 24.12 days after the earthquake. The maximum likelihood estimates of the model parameters are α=1.89, p=1.22 and b=0.72. Comparing to other earthquake sequences in China continent, the Lushan M_S7.0 earthquake sequence is characterized by a weak triggering ability in generating secondary aftershocks, a quick decay rate of aftershocks, indicating a high stress level in the aftershock region. To examine the stability of parameters, the ETAS parameters and their standard errors are estimated with different cutoff magnitudes M_c and different ending times of the fitting interval. It is observed that M_c affects the value of α significantly but has less influence on p. Furthermore, the temporal variation of the ETAS parameters changed obviously within 10 days after the main shock, but became more stable beyond this time interval.