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Determining whether the worst earthquake has passed
When a big earthquake occurs, it is hard to tell if it will be followed by a larger quake or by only smaller ones. A method has been developed that aims to distinguish between these scenarios while events are still unfolding.
After every major earthquake, seismologists warn the public that the danger has not yet passed: aftershocks will continue to shake the ground. These aftershocks usually get smaller over time, but, occasionally, an aftershock will be larger than the original event. Standard earthquake statistics suggest that the latter situation should occur about 5–10% of the time1,2, but is there any way of knowing which aftershock sequences will behave in this anomalous way? More simply, after a big earthquake, is it possible to determine whether an even larger one is coming? Writing in Nature, Gulia and Wiemer3 propose an answer to this question. They suggest that, by continuously measuring the relative numbers of large and small earthquakes, comparatively safe aftershock sequences can be distinguished from those that will get bigger.