A HUGE earthquake is predicted for Chile, after a major tremor earlier this year failed to relieve seismic stresses that have been building for 140 years.
The magnitude 8.2 Iquique quake on 1 April killed six. Now two separate analyses say worse is to come.
"Even though a very large quake has already happened this year, the hazard has not vanished," says Gavin Hayes of the US Geological Survey in Golden, Colorado. "The issue now is communicating that," he says, "as the tendency would be for people to think the quake has passed."
The risk zone stretches for 500 kilometres along much of Chile's coastline, where the Nazca tectonic plate in the Pacific burrows eastwards beneath the South American plate.
Strain has been building up since the last megaquake, a magnitude 8.8 in 1877. But Hayes's analysis suggests the April quake did not release the tension along at least two-thirds of this part of the plate boundary. The 200 kilometres south of Iquique is at most risk (Nature, DOI: 10.1038/nature13677). "Enough stress has been stored since 1877 to cause a quake of 8.5, so it means the hazard remains high," says Hayes.
It could be as large as magnitude 8.9, forecasts Bernd Schurr of the German Research Centre for Geosciences in Potsdam, Germany (Nature, DOI: 10.1038/nature13681).
"We really don't know how exactly that missing strain will ultimately be released," says Emily Brodsky of the University of California, Santa Cruz. "It could be in smaller earthquakes, slow slip events, or in a much larger one."
Fortunately Chile has good systems for responding to earthquakes, says Sergio Barrientos of the University of Chile in Santiago, a co-author on both papers. It holds major evacuation drills involving thousands of people. In coastal regions, evacuation sirens warn of impending tsunamis, and alerts are sent to cellphones and through Twitter.
This article appeared in print under the headline "Chile is facing yet another megaquake"
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