  The interevent time of terrorism attack events is investigated by empirical
data and model analysis. Empirical evidence shows it follows a scale-free
property. In order to understand the dynamic mechanism of such statistic
feature, an opinion dynamic model with memory effect is proposed on a
two-dimension lattice network. The model mainly highlights the role of
individual social conformity and self-affirmation psychology. An attack event
occurs when the order parameter of the system reaches a critical value.
Ultimately, the model reproduces the same statistical property as the empirical
data and gives a good understanding of terrorism attack.
