Residents and emergency services could better handle earthquakes if they knew whether the worst was over, or if it were still to come. Large earthquakes are often followed by aftershocks that are difficult to predict, and can sometimes be bigger than the first. Now, Swiss researchers have devised a system to help determine whether a magnitude 6.0 or greater earthquake is the main event, or merely a precursor.

Laura Gulia and Stefan Wiemer of the Swiss university ETH Zurich analysed the sequences of earthquakes in the Amatrice–Norcia region in Italy and the Kumamoto region in Japan in 2016, devising a model for predicting the threat of a larger earthquake to follow. Tested against 58 known earthquake sequences, the model identified foreshocks and aftershocks with 95 per cent accuracy.