AUSTIN (KXAN) – Researchers with the University of Texas in Austin are making some exciting discoveries beneath the Earth’s surface. A paper published in the journal Science last month revealed an unusual type of earthquake may be a result of rocks “healing.”
“If that healing is very small, then it doesn’t take very long before you can build up enough stress, to break the rock again, to overcome that healing,” said Demian Saffer, Director of the UT Institute for Geophysics and one of the lead writers of the paper.
According to Saffer, healing occurs when rocks recover following an earthquake.
“The material actually like strengthens or like heals. And, so then when you slide again and actually takes like more force for you to get it to continue to slide,” said Kaitlin Schaible, a Ph.D. student in Saffer’s Geomechanics and Geofluids Lab.
The lab created simulated earthquakes to discover how the rocks are influenced when the earth moves.
Creating ‘earthquakes’ in a lab
Inside the lab, a giant metal press sits in one corner. Its purpose: to apply pressure to a rock sample and squeeze water through it.
“You take a sediment, you just squish it like a sponge and water is going to come out,” said Peter Miller, a Ph.D. student in the lab. He’s using the machine to test how easily water moves through rocks in a fault zone, where earthquakes occur.
He uses sound waves to test changes in the rock sample, in this case gathered off the coast of New Zealand. “With a test like this, I will check in once a day, take a acoustic measurement, and then make sure everything’s looking okay.”
On the other side of the room, Schaible loads two rock samples into a metal tube. Between the samples is a piece of metal.
“You’re gonna drive this forward, and it’s going to slide along,” Schaible said while showing KXAN the device. “And so that’s simulating, like the two rocks sliding against one another.”
The metal tube that the samples are placed in creates an extremely highly pressurized zone. “So it’s like being under the earth where everything is being squeezed.”
By creating this movement and pressure, the team is able to simulate what occurs during an earthquake more than a mile beneath the surface.
Slow earthquakes and lab discovery
The slow earthquakes the team dug into occur in New Zealand, where the sample were taken from in 2018, and Japan. “It was this big discovery 20 years ago, and it kind of changed the way we think about how earthquakes work,” Saffer said.
Slow earthquakes can occur over days or even weeks. It is a slow release of the energy created as two plates rub against each other. Its such a slow release, you may not even feel the earthquake.
While a typical earthquake occurs quickly, as that energy is suddenly released, and can be one of the most destructive forces on the planet.
By looking at the rocks and simulating earthquake conditions, the team is able to see how the rocks recover after earthquakes. “We’re sampling the different rock types that might be involved in the faulting from both areas,” Saffer said.
For instance, the samples from New Zealand had more clay. Saffer said clay is slick and takes longer to heal. Slow earthquakes are more common in this area than Japan. Japan also has clay in its samples, but it is mixed with other things.
By understanding the heal rates of different types of rocks, they can determine where powerful earthquakes can occur.
“Where are the areas that are most likely to have a big earthquake? Where’s the hazard high? Where is it low? Where’s the propensity for big earthquakes to happen?”