The heat generated when rocks grind against each other during earthquakes could be a major contributor to the weakening of faults and setting the stage for a bigger tremor, scientists have found.
When rocks scrap against each other, they produce extreme heat at scattered microscopic bumps, called asperities, where they make contact. This process is similar to producing heat by rubbing your hands together, but on an extreme scale.
At major faults, such as the San Andreas in California, flashes of heat from rocks shearing past each other melts the rock. This makes the rocks slippery at those microscopic contact points, lowering the friction between them enough to trigger a significant amount of stress and setting the stage for an earthquake, the researchers said.
“These findings give us a much clearer picture of what might be happening at faults during an earthquake, and has implications on how earthquake ruptures travel within the earth,” researcher David Goldsby, a geophysicist at Brown University, was quoted as saying by OurAmazingPlanet.
To learn more about this flash heating, the scientists rubbed together different types of rocks commonly found in faults, such as quartzite and granite.
They simulated earthquake speeds of close to 1.6 feet per second (0.5 meters per second). The bumps, or asperities, each had a surface area of less than 10 microns wide, or about a tenth of the diameter of a human hair.
The researchers, who detailed their study in the journal Science, found that intense flash heating can heat asperities dramatically, perhaps up to 3,270 degrees Fahrenheit (1,800 degrees Celsius), enough to melt most rock types associated with earthquake faults.