For decades, scientists have searched for clues that would signal an impending earthquake. Teams have analyzed electromagnetic activity, weather patterns, and more only to scratch them off the list as potential harbingers of rocky destruction.

The only possible precursors that stood out were foreshocks, the tiny temblors that can occur before a larger main event. In lab experiments, foreshocks have been observed leading up to almost all simulated earthquakes. But this pattern has been missing in real earthquake data, vexing seismologists.

Now, though, a high-resolution catalog of millions of earthquakes in Southern California may have cracked the mystery.

In a recent study in Geophysical Research Letters, scientists examined a massive dataset of the region’s big and small rumbles, and they report a