Scientists at the U.S. Geological Survey (USGS) have begun studying two great Chilean earthquakes that were powerful enough to move one of its central coast islands by at least three meters, or about 10 feet.

In a study published in the journal Nature Geoscience, USGS researcher Robert Wesson and his team examined data collected from two massive earthquakes in Chile that occurred almost two hundred years apart. The first one was a magnitude 8.5 quake in 1835, while the second was a magnitude 8.8 quake in 2010.

The researchers believe the earthquakes had sufficient power to cause the island of Santa María to move vertically along the Chilean coast.

Earthquakes are known to occur when the strain built up from the movement of tectonic plates over time is suddenly released. Experts theorize that this event causes the surface of the planet to rise and fall periodically, though it remains to be proven.

The USGS researchers studied records of past Chilean earthquakes dating back to the 16th century. One of these records was made by Robert FitzRoy, captain of the HMS Beagle that brought the renowned naturalist and geologist Charles Darwin to the region in 1835.

FitzRoy wrote that the 1835 quake caused the land to rise by about two to three meters.

The would happen again almost two centuries later in 2010, during the great Maule earthquake.

Wesson and his colleagues also examined nautical survey taken from the years 1804, 1835 and 1886. They then compared this historical data with modern surveys and data gathered from the Current Population Survey to determine the vertical movement of Chile's Isla Santa María between the two great earthquakes.

The researchers found that in the 175 years between the two massive quakes, the island subsided by about 1.4 meters (4.6 feet). While the rate of the island's subsidence was not consistent, the findings show that 10 to 20 percent of movement caused by the earthquakes could be considered as permanent deformation.

Earth Observatory of Singapore researcher Aron J. Meltzner wrote in the study's accompanying article that the results of the USGS research are in accordance with the basic law concerning the movement of plates during earthquakes. The study, however, shows that the process is much more complicated than initially thought.

Meltzner explained that the variations in the behavior of the fault – whether they are weakly or strongly coupled – could occur more commonly than previously believed.

He added that Wesson and his team were able to provide evidence that the deformation of the planet's crust found in subduction zones can differ over time. The varied behavior of faults could force a reassessment of theories regarding earthquake hazards dependent on timing.

The U.S. Geological Survey study is featured in the journal Nature Geoscience.

Photo: Carlos Varela | Flickr 

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