Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Data show Antarctic ice stream radiating seismically

06.06.2008
Stick, slip, like an earthquake

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 Antarctic signals were first detected by seismographs deployed by Wiens and his colleagues in 2001-2003 at a location about 500 miles away from the ice stream.

"At first we didn't know where the waves were coming from, but eventually we were able to narrow down the source to the ice stream." Wiens said.

Slower than a real earthquake

Prior to this discovery, researchers were not aware that ice streams radiated seismic waves.

"By some measures, the seismic impact is equivalent to a very large earthquake, but it doesn't feel like it because the movement is much slower than a real earthquake," Wiens said. "The data look an awful lot like an earthquake, but the slip lasts for 10 minutes, while on the other hand an earthquake of this size would last for just ten seconds. I guess you could call it an earthquake at glacial speed. This is very strange behavior, and we need to understand more about it."

GPS instruments placed directly on the ice stream can detect where slipping motion begins and where it stops. Scientists describe the motion as "stick-slip", which is the classic motion of earthquakes, occurring when the area around a fault moves slowly but the fault is stuck, remaining stationary until the stress builds up and the fault finally slips.

"The GPS shows us directly how the ice stream moves," Wiens said. "The slip starts in a certain part of the ice stream and then it moves out, rather like a landslide might start at a certain point and then move out to envelope an entire mountainside. The GPS tells us which part moved first and what other parts moved next and so forth."

The data show that the slip always starts from the same spot on the bed of the ice stream, what glaciologists call a "sticky" spot, which has more friction than the surrounding part of the bed.

A slip, not a creep

"Glaciologists had thought that they understood how glaciers move, and they thought they move slowly and continuously by creep, but now this indicates that they move with a fast slip, almost like an earthquake," Wiens said.

The study was published in the June 5 issue of Nature on-line and was funded by the National Science Foundation.

Wiens said that it is important to understand the physics behind what is controlling this kind of slip.

"This stick-slip phenomenon may provide a clue about what makes these ice streams move faster or slower," Wiens said. "This particular ice stream has been slowing down over the last few decades, and no one knows why. "

Wiens plans to study seismic records of stick-slip events going back several decades to see if there are changes, and also to search for similar signals from other ice streams.

"We need to understand what controls the speed of the ice streams, because that will affect how fast the ice in Antarctica will go away and sea level will rise as global warming melts the West Antarctic Ice Sheet."

Douglas A. Wiens | EurekAlert!
Further information:
http://www.wustl.edu

More articles from Earth Sciences:

nachricht New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg

nachricht Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>