Earthquakes are one of the most complex natural disasters that scientists try to analyze. Although the major fault lines are well known and understood, but all the same it is very difficult to predict when a major earthquake will occur or how severe it will be.
A team of researchers from the University of Pennsylvania and Brown University have helped reveal aspect of friction at the nanoscale, which could lead to a better understanding of disaster.
Robert Karpik, a professor who heads the department of Mechanical Engineering and Applied Mechanics at the Pennsylvania School of Engineering and Applied Sciences, led the study in collaboration with Terry and David Goldsbi Tallis, professor of geological sciences from Brown.
Experimental and modeling work has been conducted Qunyang Li, who works with a group of the carp, and who was recently appointed associate professor in the School of Aerospace at Tsinghua University, China.
Team investigated the unusual phenomenon, which is observed in both natural and laboratory-simulated conditions: materials become more resistant to movement, the longer they are in contact with each other. The longer the contact material, the greater the resistance between them and the more violent and unstable the next slide. Energy is stored and then catastrophically released as an earthquake.
While the geology, physics and mechanics have studied this phenomenon for decades, the mechanism was only speculation. There are two main theories of why this is happening.
"One hypothesis is that the points of contact deform and grow over time, so the contact area increases," — says Robert Karpik. "The other — that ties at the points of contact are strengthened over time, increase the quality of contact."
"We want to simplify the business, — said Lee. — So, in our experiment, we consider only one point of contact: the tip of an atomic force microscope."
The atomic force microscope is an ideal tool to study the stability of the connection. The researchers used an atomic force microscope, working at the nanoscale, with an extremely sharp tip, working with individual atoms.
They experimented with surfaces made of various materials: diamond and graphite. Diamond and graphite are chemically inert, it is not easy to form chemical bonds with silica. Any friction occurs due to changes in the contact area.
"When you take a lot of common ground, increased rigidity and resistance to movement. But when you try to move them, you can see how great the tension and friction. So, a great influence on the mechanism by processes on a macroscopic scale."
"We do not rule out the other arguments, we just present the stronger" — says the carp.