Watts (2002): How cascades spread through social networks via threshold activation
Watts' threshold model (2002): each node activates if the fraction of active neighbors exceeds its threshold θᵢ.
Cascades exhibit a phase transition: small changes in mean threshold or connectivity cause cascade size to jump from ~0 to ~100%. The vulnerable cluster — nodes with low thresholds and low degree — determines cascade potential.
Green = active, gray = inactive, yellow = just activated.