The immense earthquake that devastated much of coastal Chile in 2010 moved ice sheets in Antarctica, almost 2,000 miles away. The 8.8-magnitude earthquake in Chile was responsible for the death of almost 500 people and the formation of a tsunami that leveled 220,000 homes.
A new study in the journal Nature Geoscience suggests that the earthquake fractured ice shelves in the Antarctic continent, triggering icequakes. It was the first time such a seeming interaction between earthquakes and icequakes in polar regions has been noted. Icequakes happen when violent earth movements cause glaciers to calve or crack into smaller sheets of ice.
A team of geological scientists gathered data from 42 seismic stations scattered throughout Antarctica and analyzed data from the six hours before and after the earthquake. 12 of the 42 stations recorded small icequakes (as indicated by high-frequency signals) which were created by seismic activity known as Rayleigh waves. Such “rolling waves” resemble ocean waves and are one of two kinds of surface waves possible, the other being Love waves.
Earthquakes are common in Antarctica and some areas can actually experience hundreds of icequakes in an hour. The present study, however, is the first to show that the ice sheets of Antarctica are sensitive to earthquakes centered in far off locations.
The seismic stations are part of the Polar Earth Observing Network (POLENET), a worldwide system that records scientific data from the polar regions. The focus is mostly on GPS and seismic data, but also takes into account geophysical observations like gravity measurement, tides and magnetics.
Equipment is stationed throughout Antarctica and Greenland. Data from POLENET provides opportunities for new understandings of Earth, its tectonic plates (the outermost shell of Earth, which is broken into seven or eight major plates), climate, the planet’s magnetic field and the “wind” that hits Earth from the sun in the form of cosmic rays.
A geophysicist on the project, Zhigang Peng, who is with Atlanta’s Georgia Institute of Technology, said that his team came across the findings by accident. In an effort to understand the 2010 earthquake, the project originally looked at data generated by stations from around South America and then “accidentally chose some stations in Antarctica.”
The study states that small and shallow earthquakes can be almost instantly triggered by seismic waves from large, yet distant, earthquakes. Antarctica is enormous. Despite dozens of seismic stations in the POLENET Antarctic network, the study notes that the actual “source locations of these triggered icequakes are difficult to determine owing to sparse seismic network coverage.” The study concludes that areas of Earth predominated by snow and ice “can be sensitive to large distant earthquakes.”
The 2010 earthquake was the largest event of its kind to hit the Southern Hemisphere after a colossal 9.5-magnitude earthquake slammed Chile in 1960. Chile is part of the seismically and volcanically active “Ring of Fire,” a circle of landmasses that generally make up the circumference of the Pacific Ocean in the Southern and Northern Hemispheres. Chile’s coastline traces the boundary where the South American tectonic plate encounters the Nazca plate and is one of the most earthquake-intensive of all countries. Chile has endured over 500 earthquakes in just the past year, although most were too slight to be felt by humans.
By Gregory Baskin