Chile's mega-quake triggered 'icequakes' in Antarctica
AFP August 12, 2014, 12:03 am TWN
PARIS--A monster earthquake that struck Chile in 2010 also unleashed minor "icequakes" in Antarctica nearly 4,700 kilometers to the south, scientists said on Sunday.
Sensors recorded small tremors in West Antarctica within six hours of the Chilean mega-shock, providing the first evidence that the world's greatest ice sheet can be affected by distant but powerful quakes, they said.
Twelve out of 42 monitoring stations dotted across the vast region showed "clear evidence" of a spike in high-frequency seismic signals, the team reported in the journal Nature Geoscience.
The signals tallied with signs of ice fractures near the surface, they added.
The Feb. 27, 2010 quake, which occurred just off the coast of Chile's Maule region, measured 8.8 in magnitude, making it one of the largest ever recorded.
It killed more than 500 people and inflicted an estimated US$30 billion (22.5 billion euros) in damages.
The main shock from the event triggered micro-quakes as far afield as North America, as the passing shock wave caused shallow faults to slip in tectonically active regions.
Geologists have long wondered how the ice sheets in Greenland and Antarctica — whose underlying rock is considered seismically peaceful — would respond to gigantic but distant quakes.
Until a few years ago, there were no means to explore the idea. But some useful tools have now become available thanks to the deployment of a small network of sensors near and on top of the sheets.
The data received after the 2010 earthquake was rather sketchy, the paper said.
The clearest signs of activity were detected at a monitoring station in West Antarctica's Ellsworth Mountains, which recorded a telltale seismic signature.
But signals received at some of the other stations were unclear or suggested nothing had happened.
The best bet is that the tremors came from movement within the ice sheet itself, and not from any fault in the bedrock below, said Zhigang Peng at the Georgia Institute of Technology in Atlanta.
"While we are not 100-percent sure, we think that those seismic signals come from ice cracking within the ice sheet, likely very close to the surface," Peng said in an email exchange with AFP.
"The main reason is that if those seismic signals were associated with faulting beneath the ice sheet, they would be similar to earthquakes at other tectonically active regions."
Put together, the data show that these vast slabs of ice can be sensitive to large, distant quakes, said the paper.
But further work will be needed to show how ice sheets respond in greater detail.
One intriguing question is the impact on features in the ice sheet — whether a big distant quake can help to rip open a crevasse or accelerate glacier flow.
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