August 11, 2014
Study Indicates 2010 Chilean Earthquake Caused Tremors In Antarctic Ice Sheet
redOrbit Staff & Wire Reports - Your Universe Online
A massive earthquake that affected the Maule region of Chile in February 2010 also unleashed a series of smaller seismic events known as “icequakes” nearly 3,000 to the south in Antarctica, a team of researchers report in a new Nature Geoscience study.
The team reported that 12 out of 42 monitoring stations in Antarctica showed evidence of a spike in high-frequency seismic signals. Those signals corresponded to signs of ice fractures occurring near the surface, suggesting that the ice cracked as the far-off seismic activity caused the Earth’s crust to shake, explained Science writer Carolyn Gramling.
“Earthquakes are already known to affect Antarctica’s ice shelves, thanks to the tsunamis they can spawn,” Gramling said. “But whether earthquake seismic waves, traveling through the ground, can chip away at Antarctica’s ice sheet – the ice piled on top of the continent – remained an unanswered question.”
Unanswered, that is, until Georgia Institute of Technology geophysicist Zhigang Peng and his colleagues happened to discover the answer while analyzing the impact of the Chile earthquake in South America. Peng’s team was looking for shallow seismic waves known as surface waves, which travel along the planet’s crust instead of reaching the mantle, when they came across data from some of the Antarctic monitoring stations during their research.
While reviewing that data in search of surface wave signals, they uncovered “tiny seismic signals” that they believed were “associated with ice cracking,” Peng told Gramling. It marked the first time scientists had found seismic evidence that an earthquake occurring so far away could register in Antarctica’s ice sheet.
“We interpret these events as small icequakes, most of which were triggered during or immediately after the passing of long-period Rayleigh waves generated from the Chilean mainshock,” Peng, an associate professor at the Georgia Tech School of Earth and Atmospheric Sciences, said in a statement. “This is somewhat different from the micro-earthquakes and tremor caused by both Love and Rayleigh-type surface waves that traditionally occur in other tectonically active regions thousands of miles from large earthquakes.”
Love waves and Rayleigh waves are the two basic types of surface waves, Gramling explained. Love waves shake the ground from side to side, while Rayleigh waves move in a rolling motion, compressing and expanding the ground as they move. Both types of surface waves can trigger micro-earthquakes, she added.
Some of the icequakes that took place lasted less than one second, while others were ten-times longer in duration, the study authors said. They took place in several different parts of the continent, including seismic stations along the coast and near the South Pole, though the clearest indication of induced high-frequency signals occurred at station HOWD, located near the northwest corner of the Ellsworth Mountains.
The AFP noted some of the signals were unclear or hinted that no seismic events had taken place. Nonetheless, Peng and his fellow researchers believe it is likely the tremors were the result of movement within the ice sheet itself, and not from any fault in the underlying bedrock.
“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,” he told the news agency via email. “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.”