] Using the same statistical physics methods they used to
] study complex systems like earthquakes and financial
] markets, Sornette and his colleagues set out to explain
] the book-ranking behavior. They used the Epidemics-Type
] Aftershock Sequence model, which draws on statistical
] techniques for studying how diseases spread through
] populations in order to model earthquake aftershocks.

This model should be applicable to the spread of memes through a population.