Figure 1. Crisis spreading model.

The dynamics of the crisis spreading model proceeds as follows: (A) Each node (country) is assigned a capacity C given by its GDP value, and two countries i and j are connected by a directed link given by the trade relation with the associated weight W_ij given by the corresponding trade volume. (B) Suppose that a country i collapses (indicated as dark brown). Then the weights of all links of country i (indicated as brown) are decreased by a fraction of f. And the total decrement ΔW of either the incoming or outgoing link weights of any countries connected to the collapsed country is compared with the fraction t of its node capacity. (C) If the total decrement exceeds the threshold for any countries, these countries also collapse (country k, in this example), triggering an avalanche of collapses. The link weights of newly-collapsed countries are decreased by the fraction f, and total decrement ΔW of each country is re-evaluated. (D) This process continues until there are no more newly-collapsed countries.