Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earthquakes generate big heat in super-small areas

14.10.2011
In experiments mimicking the speed of earthquakes, geophysicists at Brown University detail a phenomenon known as flash heating.

They report in a paper published in Science that because fault surfaces touch only at microscopic, scattered spots, these contacts are subject to intense stress and extreme heating during earthquakes, lowering their friction and thus the friction of the fault. The localized, intense heating can occur even while the temperature of the rest of the fault remains largely unaffected.


Hitting the high points
Computer-simulated topography shows high points — asperities (in red) — on the rock surface. When in contact with asperties on the adjacent surface, these asperities may undergo intense flash heating in an earthquake. Credit: Mark Robbins and Sangil Hyun, Johns Hopkins University

Most earthquakes that are seen, heard, and felt around the world are caused by fast slip on faults. While the earthquake rupture itself can travel on a fault as fast as the speed of sound or better, the fault surfaces behind the rupture are sliding against each other at about a meter per second.

But the mechanics that underlie fast slip during earthquakes have eluded scientists, because it’s difficult to replicate those conditions in the laboratory. “We still largely don’t understand what is going at earthquake slip speeds,” said David Goldsby, a geophysicist at Brown, “because it’s difficult to do experiments at these speeds.”

Now, in experiments mimicking earthquake slip rates, Goldsby and Brown geophysicist Terry Tullis show that fault surfaces in earthquake zones come into contact only at microscopic points between scattered bumps, called asperities, on the fault. These tiny contacts support all the force across the fault. The experiments show that when two fault surfaces slide against other at fast slip rates, the asperities may reach temperatures in excess of 2,700 degrees Fahrenheit, lowering their friction, the scientists write in a paper published in Science. The localized, intense heating can occur even while the temperature of the rest of the fault remains largely unaffected, a phenomenon known as flash heating.

“This study could explain a lot of the questions about the mechanics of the San Andreas Fault and other earthquakes,” said Tullis, professor emeritus of geological sciences, who has studied earthquakes for more than three decades.

Hitting the high points

Computer-simulated topography shows high points — asperities (in red) — on the rock surface. When in contact with asperties on the adjacent surface, these asperities may undergo intense flash heating in an earthquake.

Credit: Mark Robbins and Sangil Hyun, Johns Hopkins UniversityThe experiments simulated earthquake speeds of close to half a meter per second. The rock surfaces touched only at the asperities, each with a surface area of less than 10 microns — a tiny fraction of the total surface area. When the surfaces move against each other at high slip rates, the experiments revealed, heat is generated so quickly at the contacts that temperatures can spike enough to melt most rock types associated with earthquakes. Yet the intense heat is confined to the contact flashpoints; the temperature of the surrounding rock remained largely unaffected by these microscopic hot spots, maintaining a “room temperature” of around 77 degrees Fahrenheit, the researchers write.

“You’re dumping in heat extremely quickly into the contacts at high slip rates, and there’s simply no time for the heat to get away, which causes the dramatic spike in temperature and decrease in friction,” Goldsby said.

“The friction stays low so long as the slip rate remains fast,” said Goldsby, associate professor of geological sciences (research). “As slip slows, the friction immediately increases. It doesn’t take a long time for the fault to restrengthen after you weaken it. The reason is the population of asperities is short-lived and continually being renewed, and therefore at any given slip rate, the asperities have a temperature and therefore friction appropriate for that slip rate. As the slip rate decreases, there is more time for heat to diffuse away from the asperities, and they therefore have lower temperature and higher friction.”

Flash heating and other weakening processes that lead to low friction during earthquakes may explain the lack of significant measured heat flows along some active faults like the San Andreas Fault, which might be expected if friction was high on faults during earthquakes. Flash heating in particular may also explain how faults rupture as “slip pulses,” wrinkle-like zones of slip on faults, which would also decrease the amount of heat generated.

If that is the case, then many earthquakes have been misunderstood as high-friction events. “It’s a new view with low dynamic friction. How can it be compatible with what we know?” asked Tullis, who chairs the National Earthquake Prediction Evaluation Council, an advisory body for the U.S. Geological Survey.

“Flash heating may explain it,” Goldsby replied.

The U.S. Geological Survey funded the research.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

Richard Lewis | EurekAlert!
Further information:
http://www.brown.edu

More articles from Earth Sciences:

nachricht Seabed mining could destroy ecosystems
23.01.2018 | University of Exeter

nachricht How climate change weakens coral 'immune systems'
23.01.2018 | Ohio State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Optical Nanoscope Allows Imaging of Quantum Dots

Physicists have developed a technique based on optical microscopy that can be used to create images of atoms on the nanoscale. In particular, the new method allows the imaging of quantum dots in a semiconductor chip. Together with colleagues from the University of Bochum, scientists from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute reported the findings in the journal Nature Photonics.

Microscopes allow us to see structures that are otherwise invisible to the human eye. However, conventional optical microscopes cannot be used to image...

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Rutgers scientists discover 'Legos of life'

23.01.2018 | Life Sciences

Seabed mining could destroy ecosystems

23.01.2018 | Earth Sciences

Transportable laser

23.01.2018 | Physics and Astronomy

VideoLinks Science & Research
Overview of more VideoLinks >>>