The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them)

by Lucy Jones

The argument that formed the basis of De Bernardinis and Bertolaso’s reassurances—that small earthquakes reduce the risk of big earthquakes—is patently false. It is a bit of folk wisdom, one that I am asked about frequently, and that arises from nothing so much as wishful thinking. Big earthquakes release more energy than small ones. If we have a lot of small ones, the argument goes, shouldn’t that release the pent-up energy? While it makes intuitive sense, it contradicts the most consistent feature of earthquakes we’ve observed—one that Charlie Richter saw in the first set of earthquakes for which he calculated magnitudes, that we see in every aftershock sequence, and that occurs in any regional grouping of earthquakes around the world. The relative number of small to large earthquakes is constant. More small earthquakes means more big ones. Mathematicians call this a self-similar distribution.