Comparison of Early Aftershock Forecasting for the 2008 Wenchuan MS8.0 Earthquake

The M(S)8.0 earthquake that occurred in Wenchuan, Sichuan in 2008 provides an important case for the study of operational earthquake forecasting and short-term aftershock forecasting of major disaster-inducing earthquakes in China. This paper focuses on the comparative study of the applicability of the epidemic-type aftershock sequence (ETAS) model, the Reasenberg-Jones (R-J) model and the Omi-R-J model, which are widely adopted internationally for short-term aftershock forecasting and seismic hazard mitigation strategy research. We compare the stability of model parameters and aftershock occurrence rate forecasting, and evaluate the effectiveness of forecasting using the N-test and T-test with multiple time windows. The results show that the sequence parameters of the ETAS model, the R-J model and the Omi-R-J model tend to stabilize after 15.50, 15.50 and 6.00 days following the earthquake respectively, and the attenuation of the Wenchuan M(S)8.0 earthquake is rather normal. Compared to the ETAS model and the R-J model, the Omi-R-J model obtain steadier model parameters in a shorter time with significantly smaller parameters p(ORJ), c(ORJ), b(ORJ) and standard deviations. Among the three models, the overall aftershock occurrence rate forecasted by the R-J model is the highest, followed by the Omi-R-J model, while that of the ETAS model is the lowest. N-test results show overall forecasting effectiveness of 93.8, 80.7 and 97.7% for the ETAS, R-J and Omi-R-J models, respectively, with the ETAS and Omi-R-J models superior to the R-J model, and the Omi-R-J model slightly better than the ETAS model. The overall "information gain per earthquake" calculation results show that the ETAS model is superior to the Omi-R-J and R-J models, while the Omi-R-J model is better than the R-J model; thus the combined use of the ETAS and Omi-R-J models by focusing on their respective strengths might ensure optimal performance. These "maneuverable" forecasting approaches to short-term aftershock model forecasting will play a vital role in efficient post-disaster relief, emergency management decision-making and post-disaster reconstruction.