HU study creates new approach to understanding earthquakes

Principles could eventually lead to ability to defuse or at least warn of tremors.

By
March 8, 2010 02:12
Firemen work on a destroyed building in Concepcion

Chile earthquake cool night buildings falling over 311 ap. (photo credit: ASSOCIATED PRESS)

 
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Although many years will pass before mankind will be able to predict when and where an earthquake will erupt, and even preemptively defuse the potentially devastating underground forces, an Israeli physicist has developed an entirely new approach to the subject by studying and measuring friction in his Jerusalem lab.

Earthquakes occur when tectonic plates kilometers beneath the Earth’s surface, break loose from the frictional forces that usually hold them together as they are constantly being shoved against each other.

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Prof. Jay Fineberg, a physicist and the Max Born Professor of Natural Philosophy at the Hebrew University of Jerusalem, along with doctoral students Oded Ben-David and Shmuel Rubinstein, suggest a new approach to quakes in an article recently published in the prestigious journal Nature.

Titled “Slip-stick and the evolution of frictional strength,” it is based on their work using blocks of acrylic glass (Plexiglass) that they rubbed against each other, using lasers to measure the frictional forces between them. A further reference to their new approach appeared in Nature Physics.

The lab experiments, which took five years to prepare and conduct, involved the same principles as those that occur before earthquakes. The team showed how frictional strength evolves over time.

Friction is involved in both natural phenomena and man-made ones such as braking a car, rolling a bowling ball toward pins, inserting and removing digital data from computer hard drives and skiing on water or snow.

“Although friction plays such an important role in so many aspects of our lives, it is surprising that many key processes embodied within frictional motion have been far from understood,” Fineberg told The Jerusalem Post in an interview on Sunday.



While friction, even between pieces of glass, is often thought of as resulting from motion between perfectly smooth surfaces, all sliding surfaces have microscopic bumps. Only the edges of these bumps are in contact with each other, rather than the entire surface, said Fineberg, who came on aliya from Pennsylvania in 1972 for physics studies at HU.

“Thus all of the contact between sliding bodies takes place in only a tiny area, and the bumps are responsible for maintaining the contact between two sliding bodies. It is the behavior of these bumps that governs friction,” he said.

Millionths of seconds before bodies start to slide against one another, a tiny “earthquake” tears through the interface and ruptures the contacts, said Fineberg.

From that moment of contact, four distinct and interrelated phases of evolution are identified, he said. These are the violent rupture phase, resultant contact weakening, renewal and re-strengthening. These results provide a comprehensive picture of how frictional strength evolves, he explained.

The HU scientists “realized that the same frictional forces” involved in their tabletop experiments “control the movement of tectonic plates. Our empirical findings suggest that there is a reduction in contact strength caused by the breaking of microcontacts just before the two blocks move relative to another.

“The speed at which microcontacts re-attach depends on how fast the sliding occurs. Understanding this behavior may help us to better predict earthquakes and their potential for damage,” Fineberg said.

In 2004, Fineberg and colleagues published in Nature a study on the early stages of their research related to earthquakes.

“But now we were the first to measure the strength of each micropoint, learning some of the rules of friction that change at the same scale at which quakes occur. We have produced high-resolution measurements of actual vibrations. Before, we could only guess. Our approach is relevant to many things, such as any object you push across your desk; the same physics applies.”

Although scientists have been studying earthquakes for almost a century, said Fineberg, “it is amazing that very little is known. Seismologists don’t really know what is going on; they can listen to the sounds of friction between tectonic plates, but most of the data from seismic waves are lost as they travel between 15 and 100 kilometers below the Earth’s surface.

“What results is very limited information,” he noted. “But using the physical principles of near-field optics, we have developed a new way of actually measuring in real time – in millionths of seconds – the results of motion and the real contact area between the two blocks. The strength of material is the glue that holds the fault together.”

He predicted the new approach will lead to next-generation findings.

“While the HU team’s findings have aroused much interest in the scientific community, they are controversial among some,” he said.

Fineberg said he would be disappointed if they didn’t, and agreed that this often occurs when new approaches are presented.

Fineberg believes that if the world had even a second of advance notice before a potentially devastating earthquake, a lot of peripheral damage from electricity or gas mains could be prevented. These could be programmed to shut down automatically when the relevant forces of friction break down, he said.

“This could prevent a lot of deaths. One doesn’t want to do this if not necessary, so the advance warning must be absolutely reliable.”

In addition, even farther into the future, the forces of earthquakes could possibly be defused.

“If mankind could reach an advanced level of knowledge, perhaps it could generate a small earthquake to release subterranean pressures along fault lines,” Fineberg suggested.

“Even today, people searching for oil have triggered quakes by pumping water into a well that was near a fault. If you’re lucky, you dig a hole and hit a pocket of oil. Trucks pump in pressurized water to create cracks that connect to other pools of oil.”

One would not have to explode atomic bombs to defuse earthquakes, he predicted.

As the Jordanians are planning to dig a Dead Sea-Red Sea canal (adopting an Israeli idea whose application has been delayed) along the Syrian-African fault – which is the most dangerous in the area – Fineberg said that such earthwork “could alleviate underground pressures or trigger an earthquake – or have no effect at all. Nobody knows, but it should be studied.

“I would be thrilled to work with scientists in Jordan or other countries. But we’re not even close to the point when we can advise people what to do to prevent or cause earthquakes. If we’re lucky, our children will benefit from this research.”

Fineberg said that he “couldn’t get anyone interested in financing his 2004 research, but the new phase was a joint project funded by the Israel Science Foundation and the European Union.”  

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