Statistical analysis of ETAS parameters in the early stage of the 2013 Lushan M_S7.0 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.