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Chilean earthquake triggered icequakes in Antarctica

Quake cracks Chile's deadly 2010 earthquake triggered icequakes thousands of kilometres away in Antarctica, according to a new study.

The findings, reported in the journal Nature Geoscience, are the first documented evidence of ice sheets being ruptured by a large distant quake.

Large earthquakes are known to trigger distant seismic activity in the Earth's crust.

These new findings highlight a previously little understood interaction between the solid Earth and the frozen liquid portion of the crust, say the researchers.

"I was surprised and we were all excited because no one had ever seen this before," says study co-author Dr Jake Walter, who was working with the Georgia Institute of Technology at the time of the research, and is now at the University of Texas.

"This tells us something new about the way the Earth works, and potentially changes our understanding of the way earthquakes proliferate into icefields."

The magnitude 8.8 earthquake, which rocked Maule in central Chile in late February 2010 killing over 700 people, lasted for three minutes. It was the sixth largest earthquake ever recorded by a seismograph.

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Walter and colleagues analysed seismic data from 42 Antarctic stations that had been recorded in the six-hours before and after the earthquake.

The data revealed no icequakes were recorded prior to the quake.

However, 12 stations recorded small icequakes occurring in the hours immediately following the earthquake.

"Icequakes happen when glaciers calve, or when crevasses open up as they move and slide along their bed, says Walter.

Walter and colleagues believe these icequakes were triggered by seismic surface waves radiating away from the earthquake's epicentre and passing through the ice sheet.

Seismic waves move differently depending on the material they're travelling through.

"The waves slow down in ice compared to rock, because the ice is softer and elastic," says Walter.

The source of these small icequakes is thought to be a crevasse that's opening up.

"A crevasse has its own orientation, so earthquakes coming from different directions and at different strengths may affect a crevasse differently," says Walter.

"For example if it doesn't come at the right angle it may not trigger an icequake."

An earthquake's ability to trigger an icequake is also likely to be dependant both on the strength and distance of the initial earthquake, and on how stressed the ice is at the time.

"This is the first event that we've looked at, and we have plans to look at other events to see what other kinds of behaviours we can find," says Walter.