NEW YORK, Apr 29: Earthquakes can permanently crack the Earth, a study of quakes that have rocked Chile over the past million years has suggested.
Previous research has found that Earth mostly rebounds after quakes, with blocks of the world’s crust elastically springing back, over the course of months to decades, to the way they initially were.
Such rebounding was first seen after investigations of the devastating 1906 San Francisco temblor that caused destruction of more than 80 per cent of the city, website ‘OurAmazingPlanet’ reported.
The rebound is well-documented now by satellite-based Global Positioning System (GPS) systems that monitor Earth’s movements.
However, structural geologist Richard Allmendinger of Cornell University and his colleagues in the new study found that major earthquakes of magnitude 7 or greater apparently caused the crust in northern Chile to crack permanently.
“My graduate students and I originally went to northern Chile to study other features. While we were there, our Chilean colleague, Professor Gabriel Gonzalez of the Universidad Catolica del Norte, took us to a region where these cracks were particularly well-exposed,” Allmendinger told the website.
In northern Chile, “the driest place on Earth, we have a virtually unique record of great earthquakes going back a million years,” Allmendinger said.
Whereas most analyses of ancient earthquakes only probe cycles of two to four quakes, “our record of upper plate cracking spans thousands of earthquake cycles,” he noted.
The record of the vast number of earthquakes captured in northern Chilean rocks allowed the researchers to examine their average behaviour over a much longer period of time, which makes it easier to pick out any patterns.
They discovered that a small but significant 1 to 10 per cent of the deformation of the Earth caused by 2,000 to 9,000 major quakes over the past 800,000 to 1 million years was permanent, involving cracks millimetres to meters large in the crust of the Atacama Desert.
The crust may behave less elastically than previously thought.
“It is only in a place like the Atacama Desert that these cracks can be observed – in all other places, surface processes erase them within days or weeks of their formation, but in the Atacama, they are preserved for millions of years,” Allmendinger said.
“We have every reason to believe that our results would be applicable to other areas, but is simply not preserved for study the way that it is in the Atacama Desert,” he added.
The study was published in the journal Nature Geoscience. (PTI)
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