An everyday physics quirk could be an important missing piece in scientists’ efforts to predict the world’s strongest earthquakes. In a study published in the journal Science, researchers from the University of Texas at Austin found that friction could be the key to understanding when and how violently bugs move. That’s because this phenomenon, which explains why it takes more effort to push a heavy box from rest than to keep it moving, determines how quickly fault surfaces connect or heal after an earthquake.
A fault that heals slowly is more likely to move harmlessly, while a fault that heals quickly is more likely to stick around until it ruptures in a large, destructive earthquake. The discovery could be the key to understanding when and how violently the faults move. That alone won’t allow scientists to predict when the next big earthquake will strike the forces behind big earthquakes are too complex but it gives researchers a valuable new way to study the causes and potential of a large, destructive earthquake. happened, the authors said.
“The same physics and logic should apply to all the different kinds of faults around the world,” said study co-author Demian Saffer, director of the University of Texas Geophysics Institute at the Jackson School of Geosciences. “With the right samples and field observations, we can now begin to make testable predictions about how large and how often large seismic slips may occur on other large faults such as Cascadia in the Pacific Northwest.”
To make the discovery, the researchers devised a test that combined rocks from a well-explored fault off the coast of New Zealand and a computer model to successfully calculate that a harmless kind of “slow motion” earthquake would occur every few years because the clay-rich rocks in the fault heal very slowly.
The rock samples the researchers tested were drilled about half a mile below the seafloor in a fault in New Zealand. They pressed the rocks in the fault area in a hydraulic press and found that they healed very slowly and slid easily. When they fed the rock data into a computer model of the fault, the result was a small, slow-motion tremor every two years, an almost exact match with observations from the New Zealand fault.
Scientists believe that the clay-rich rocks common to many large faults could regulate earthquakes by allowing the plates to slide quietly past each other, limiting the build-up of stress. The discovery could be used to determine whether the fault is prone to slip in large, damaging earthquakes, said study co-leader Srisharan Shreedharan, an associate researcher at the University of Texas Institute for Geophysics and an assistant professor at Utah State University.
“That doesn’t get us any closer to actually predicting an earthquake, but it does tell us whether the fault is likely to slip quietly without an earthquake, or whether it’s likely to have large earthquakes,” he said. There is little evidence of shallow, slow-motion tremors in Cascadia. That’s one reason the Pacific Northwest Seismic Network wants to place sensors in key fault areas. The new study gives them a framework to do that, said network director Harold Tobin.
“We want to focus on the processes in the shallow part of the fault, because that’s what controls the size of the tsunami,” said Tobin, who was not part of the study. “Fault healing doesn’t explain everything, but it gives us a window into how subduction zone faults work that we didn’t have before.”
The research was funded by the University of Texas Geophysical Institute, the International Ocean Discovery Program and New Zealand’s GNS Science. Rock samples from New Zealand were collected during the 2018 Ocean Drilling Science Mission, co-led by Saffer and Laura Wallace, a scientist at the University of Texas Institute for Geophysics and GNS Science in New Zealand. Co-authors included Wallace and Charles Williams, also of GNS Science, who collaborated on computer modeling of the study.
