Real physics of earthquakes remains unclear
The earthquake does not depend on increasing the number of contacts between the tectonic plates, and from changes in the quality of these contacts, set up two groups of geophysicists. Understanding of the physics of tectonic friction helps in predicting major earthquakes.
United group of physicists-engineers and geologists from the University of Pennsylvania and Brown University, published in the Today's issue of the journal Nature
report on the experiment, the results of which can be used to predict a major earthquake — the tasks for today insoluble.
Solve one of the mysteries of geophysics helped atomic force microscope
Watching the real shifts of tectonic plates and their laboratory counterparts, researchers have long noticed an unusual phenomenon, and difficult to explain:
sliding friction of two pressed together materials becomes greater, the longer they are in contact.
This effect is critical to the understanding of how earthquakes occur and why they occur at all. It defines the destructive energy that is released when the tectonic plates overcome, finally, the increased friction and move relative to each other.
Theoretically explain why the friction increases with time 'no binomial theorem ": there are two major and very logical hypotheses on the causes of this so-called 'frictional aging ". According to one friction increases due to the fact that over time, deformed and pressed against the surface of the contact points between them increases, leading to an increase in the frictional force. Another hypothesis explains what is happening does not increase the number of points of contact and adhesion forces between them, the increase is said to mechanics, the quality of the contact.
It was obvious that, most likely, both mechanisms are working here, but which one is the defining, so far failed to establish.
The problem was that these same points of contact between the two surfaces are therefore not open to observation. Some, however, were able to establish contact points for observing compression of two transparent plates: in fact, their number increased over time. This seems to be spoken in favor of the first hypothesis, but in reality, nothing to give, because it has not turned out to estimate the strength due to these points or even safe to say that this is the point of contact, not clusters of small dots of reach observing nanoscale.
Met once at a conference, Physics of Pennsylvania and Brown University geologists suddenly found that first the heater capable of solving the problem of the second, namely the atomic force microscope — an ideal way to assess the quality of the point of contact, that is, the coupling strength, which arises at this point .
The atomic force microscope allowed to move on to the real earthquakes megamasshtaba nanoscale.
That is, to a single point as determined by the size of the probe tip, which in this microscope, measurements, and so accurate that allows you to feel the impact of individual atoms.
Researchers have recreated the conditions at that point of contact 'silicon-silicon. " Clutching a silicon tip of the microscope to the silicon surface, they kept them in this state for a while, and then drags the tip over the surface and measure the force of friction. The same thing they did for the diamond and graphite surfaces.
The results surprised me.
Contact 'silicon-silicon " (that is what is happening in the tectonics) led to a very significant 'frictional aging ", while the silicon contact with graphite or diamond virtually to any increase in the friction force does not lead.
This meant that in frictional aging that occurs in the tectonic processes, the main role is played not by the number of points of contact, and the growth of the force due to these points. Whether it differently, a substantial increase in forces in the individual point atomic force microscope would not have noticed.
However, the solution of a puzzle spawned another. Frictional aging contacts 'silicon-silicon "were much more powerful than that which is observed in the macro scale during earthquakes. The second riddle, however, immediately and resolved. It turned out that each contact point your character and its quality: some are more strongly bound, others less, some are beginning to move sooner, others later, and the weak points of a lot more.
'This is just the beginning, "- says his discovery of the author.
'The main thing is that we understand the physics of the process, evaluated its qualitative aspect. Now it is necessary to quantify. You need to assess what levels of stress at the quality of contact comes into play, you also need to study these processes at different temperatures, to monitor them in real time with an electron microscope. "