Antarctic ice stream radiates seismically: sticks, slips like an earthquake

Science Daily: A seismologist at Washington University in St. Louis and colleagues at Pennsylvania State University and Newcastle University in the United Kingdom have found seismic signals from a giant river of ice in Antarctica that makes California's earthquake problem seem trivial. Douglas A. Wiens, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, and colleagues combined seismological and global positioning system (GPS) analyses to reveal two bursts of seismic waves from an ice stream in Antarctica every day, each one equivalent to a magnitude seven earthquake. The GPS analyses were performed by Pennsylvania State and Newcastle University researchers.

The ice stream is essentially a giant glacier 60 miles wide and one-half mile thick. The data show that the river of ice moves about 18 inches within ten minutes, remains still for 12 hours, then moves another eighteen inches. Each time it moves, it gives off seismic waves that are recorded at seismographs all around Antarctica, and even as far away as Australia. Seismic waves from what are loosely called "glacial earthquakes," mainly near Greenland, were originally reported in 2003, and the numbers have been increasing in recent years. Some scientists think the waves come from the phenomenon of calving, where a big chunk of ice breaks off of a glacier and floats away in the ocean, a very violent activity that could generate strong seismic signals. The new results show that at least some of the glacial earthquakes are produced by sudden sliding of large ice sheets.

The Garwood Glacier in Antarctica, National Science Foundation, Wikimedia Commons