The vertical movement of an island off the coast of central Chile after two great earthquakes in 1835 and 2010, and during the 175 years in between, is reported in a study published online in Nature Geoscience. The data used include records taken in 1835 by Robert FitzRoy, the captain of the HMS Beagle during Charles Darwin's journey, and suggest that 10 to 20% of earthquake-induced uplift could be permanent.
While two tectonic plates are locked together, strain accumulates over a period of decades or centuries. This accumulated strain is suddenly released when the plates slip past each other in an earthquake. Earth’s surface is thought to rise and fall cyclically in the course of this cycle.
Robert Wesson and colleagues analysed nautical surveys from 1804, 1835 and 1886 together with modern surveys and GPS data to quantify the vertical movement of Isla Santa Maria during the complete cycle between the two earthquakes. The authors found that the island was uplifted by 2.4 m to 3 m following the 1835 earthquake and by 1.8 m following the 2010 earthquake, but it subsided by only 1.4 m in the intervening period. They also note that subsidence between the two quakes unexpectedly did not occur at a uniform rate.
In an accompanying News & Views, Aron Meltzner writes that the approach of the authors could be used to "quantify the amount of slip waiting to occur on a fault […], a potentially useful tool for anticipating impending large earthquakes.”
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