We know this much: Earthquakes strike along faults—fractures in the planet’s crust where plates of rock are thrust into a sort of geological gridlock. The difference between a tremor and an earth-shattering 8.0-plus-magnitude quake depends on whether the plates slip when the tension between them is still relatively low or if they snap after enduring millennia of mounting strain.

Calculating exactly when this might happen, however, is no easy feat.