The powerful 8.3 magnitude earthquake that hit Chile overnight was partly a consequence of a massive nearby quake in 2010. But the release of stress from this latest quake does not relieve the risk of an even larger earthquake expected further north. Tsunami warnings have been issued on both sides of the Pacific.
The hit at just before 11 pm at a depth of 25 kilometres, off the coast of Coquimbo, 230 kilometres north of Santiago in Chile.
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Early reports suggest at least five people have been killed and millions have been evacuated from the nearby Chilean coast, as spread around the Pacific. Waves 4.6 metres high and tsunami warnings are active for California and New Zealand.
Seismologists say the event is linked to one from 2010. In February that year, a quake of 8.8 magnitude killed more than 700 people and shifted the Earth鈥檚 axis.
Earthquakes happen along the coast of Chile because the Nazca plate under the Pacific Ocean is moving towards, and slipping under, the South American plate. It鈥檚 moving at a rate of about eight centimetres every year. The friction between the plates creates tension that builds up, and is then released when the plates slip, creating earthquakes.
The massive 2010 earthquake released tension in a very large part of the fault, but the slipping stopped at a pile of underwater mountains called the Juan Fern谩ndez Ridge. 鈥淭his one that happened this evening of where the last one finished,鈥� says from Penn State University.
That meant that the section which slipped today was ready to slip, says Furlong. But it also put extra stress on the remaining fault. 鈥淏ecause if the one next to it moves, and it didn鈥檛, it sort of gets twisted and torqued a bit,鈥� he says.
It鈥檚 unclear yet if the earthquake has relieved the stress in that region, lowering earthquake risk in the coming years. 鈥淭hat鈥檚 probably information that will come out in the coming days,鈥� says from the US Geological Survey.
鈥淏ut looking at the history of large earthquakes in the region, there was a significant earthquake on this same section in 1943 and just to the north in 1922. So it hasn鈥檛 had a big event in 70 years. So it has been accumulating strain energy for a long time.鈥�
But just as this quake was waiting to happen since 2010, other parts of the Chilean fault are expected to go soon too. Just last year a powerful quake struck further north near the border with Peru, killing six people.
As Hayes, Furlong and others showed recently that quake failed to release stress building up for over a century, and added additional stress to the region just south of it. A devastating quake relieving the remaining stress could be as big as 8.9, Hayes says.
