News that doesn't receive the necessary attention.

Monday, August 11, 2014

2010 Chile earthquake caused West Antarctic ice to crack and calve, discovery made with new technology, scientist co-author 'surprised'-Nature Geoscience

8/11/14, "‘Icequakes’ In Antarctica Triggered By Massive 2010 Earthquake In Chile," International Business Times, Philip Ross
 

"A massive earthquake that struck Chile in 2010 caused glaciers thousands of miles away in Antarctica to calve, a study published Sunday in the journal Nature Geoscience found. Seismic surface waves radiating away from the earthquake’s epicenter traveled some 2,900 miles (4,700 kilometers) before passing through Antarctica’s ice sheets and causing small tremors, or “icequakes.”

The study is the first time researchers have documented evidence of ice sheets being ruptured by large but distant earthquakes. The research may help scientists better understand how earthquakes impact Antarctic ice, a phenomenon that, until recently, raised more questions than answers. New technology has made studying icequakes possible in recent years.

"This tells us something new about the way the Earth works, and potentially changes our understanding of the way earthquakes proliferate into icefields,” study co-author Jake Walter, who was with the Georgia Institute of Technology at the time of the research, told ABC. “I was surprised and we were all excited because no one had ever seen this before.”

The massive magnitude 8.8 earthquake that occurred off the coast of central Chile Feb. 27, 2010, is the sixth largest earthquake ever recorded by a seismograph. The tremor killed more than 500 people and caused an estimated $30 billion in damage. Buildings were destroyed, bridges collapsed and electricity, water and phone lines cut. The effects of the quake were seen some 4,785 miles (7,700 kilometers) away in French Polynesia where high waves swept ashore but caused no reported damage.

Walter and a team of researchers from the Georgia Institute of Technology studied seismic data from 42 monitoring stations in Antarctica that had been recording in the six hours before and after the quake. Twelve of the 42 stations showed a spike in high-frequency seismic signals that corresponded with ice fractures near the surface.

"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," Zhigang Peng, associate professor at Georgia Institute of Technology and lead author of the study, told 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.""

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8/10/14, "Antarctic icequakes triggered by the 2010 Maule earthquake in Chile," Nature Geoscience, Nature.com
"Seismic waves from distant, large earthquakes can almost instantaneously trigger shallow micro-earthquakes and deep tectonic tremor as they pass through Earth’s crust1. Such remotely triggered seismic activity mostly occurs in tectonically active regions. Triggered seismicity is generally considered to reflect shear failure on critically stressed fault planes and is thought to be driven by dynamic stress perturbations from both Love and Rayleigh types of surface seismic wave2. Here we analyse seismic data from Antarctica in the six hours leading up to and following the 2010 Mw 8.8 Maule earthquake in Chile. We identify many high-frequency seismic signals during the passage of the Rayleigh waves generated by the Maule earthquake, and interpret them as small icequakes triggered by the Rayleigh waves. The source locations of these triggered icequakes are difficult to determine owing to sparse seismic network coverage, but the triggered events generate surface waves, so are probably formed by near-surface sources. Our observations are consistent with tensile fracturing of near-surface ice or other brittle fracture events caused by changes in volumetric strain as the high-amplitude Rayleigh waves passed through. We conclude that cryospheric systems can be sensitive to large distant earthquakes."
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8/11/14, "Chile quake triggered 'icequakes'," AFP via technology.iafrica.com

"A monster earthquake that struck Chile in 2010 also unleashed minor "icequakes" in Antarctica nearly 4700 kilometres 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 February 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 $30-billion 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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6/10/14, "Underground Volcanoes Responsible For Glacier Melting In Western Antarctica," IBT, Kukil Bora




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