Earthquake risk has not risen

16 November 2011
Nature 479

A spate of large earthquakes has shaken the world in recent years, with five reaching a magnitude greater than 8.5 since 2004. This has led some to question whether earthquakes come in clusters, and whether, at present, the risk of large quakes is temporarily above the norm. But Andrew Michael of the US Geological Survey in Menlo Park, California, shows that apparent clusters of large quakes in the global record are indistinguishable from random variability.

He applied three classes of statistical tests to earthquakes of magnitude greater than 7 that have occurred since 1900, and omitted the localized aftershocks connected to each quake. He demonstrates that similar clusters would still be found if the quakes were independent, random events occurring at a low but constant average rate. He concludes that the risk of future earthquakes has not increased, except within ongoing aftershock sequences.

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