Earthquake scientists have a new tool in the race to find the next big one
IMAGE: A SEISMOGRAPH RECORDS SEISMIC ACTIVITY NEAR THE SAN ANDREAS FAULT. NEW RESEARCH FROM THE UNIVERSITY OF TEXAS AT AUSTIN JACKSON SCHOOL OF GEOSCIENCES COULD AID IN PREDICTING THE WORLD’S MOST POWERFUL EARTHQUAKES. view more
CREDIT: RAY_EXPLORES/FLICKR HTTPS://FLICKR.COM/PHOTOS/RAYBOUK/8201310617/
An everyday quirk of physics could be an important missing piece in scientists' efforts to predict the world’s most powerful earthquakes.
In a study published in the journal Science, researchers at The University of Texas at Austin discovered that a frictional phenomenon could be key to understanding when and how violently faults move. That’s because the phenomenon, which explains why it takes more effort to shove a heavy box from a standstill than it does to keep it moving, governs how quickly the fault surfaces bond together, or heal, after an earthquake. A fault that is slow to heal is more likely to move harmlessly, while one that heals quickly is more likely to stick until it breaks in a large, damaging earthquake.
The discovery could be key to understanding when, and how violently, faults move. That alone won’t allow scientists to predict when the next big one will strike — the forces behind large earthquakes are too complex — but it does give researchers a valuable new way to investigate the causes and potential for a large, damaging earthquake to happen, the authors said.
“The same physics and logic should apply to all different kinds of faults around the world,” said the study’s co-lead author Demian Saffer, director of the University of Texas Institute for Geophysics at the Jackson School of Geosciences. “With the right samples and field observations we can now start to make testable predictions about how big and how often large seismic slip events might occur on other major faults, like Cascadia in the Pacific Northwest.”
To make the discovery, researchers devised a test that combined rocks from a well-studied fault off the coast of New Zealand and a computer model, to successfully calculate that a harmless kind of “slow motion” earthquake would happen every few years because the clay-rich rocks within the fault are very slow to heal.
The rock samples the researchers tested were drilled from about half a mile under the seafloor in a fault in New Zealand. They squeezed the fault zone rocks in a hydraulic press and found that they were very slow to heal and slipped easily. When they plugged the rock data into a computer model of the fault, the result was a small, slow-motion tremor every two years, a near exact match with observations from the New Zealand fault.
The researchers think the clay-rich rocks, which are common at many large faults, could be regulating earthquakes by allowing plates to slip quietly past each other, which limits the buildup of stress. The discovery could be used to determine whether a fault is prone to slipping in large, damaging earthquakes, said study co-lead Srisharan Shreedharan, affiliate researcher at the University of Texas Institute for Geophysics and assistant professor at Utah State University.
“This doesn't get us any closer to actually predicting earthquakes, but it does tell us whether a fault is likely to slip silently with no earthquakes, or have large ground-shaking earthquakes,” he said.
At Cascadia, there is little evidence of shallow, slow-motion tremors. That’s one of the reasons the Pacific Northwest Seismic Network wants to place sensors across key areas of the fault. The new study gives them the framework to do so, said network Director Harold Tobin.
“We want to zero in on the processes in the shallow part of the fault because that’s what governs the size of the tsunami,” said Tobin, who was not part of the study. “Fault healing doesn’t explain everything, but it does give us a window into the working of subduction zone faults that we didn’t have before.”
The research was funded by the University of Texas Institute for Geophysics, the International Ocean Discovery Program, and New Zealand’s GNS Science. The New Zealand rock samples were gathered during a 2018 scientific ocean drilling mission co-led by Saffer and Laura Wallace, a research scientist at University of Texas Institute for Geophysics and GNS Science in New Zealand. Coauthors included Wallace and Charles Williams, also at GNS Science, who collaborated on the study’s computer modeling.
Demian Saffer, director of the University of Texas Institute for Geophysics (UTIG) and Laura Wallace, a UTIG research scientist, examine rock samples drilled from about half a mile under the seafloor in a fault in New Zealand during a 2018 scientific ocean drilling mission that they co-led. Lab tests revealed that clay-rich rocks are regulating earthquakes there by allowing the fault to slip harmlessly.
CREDIT
Tim Fulton, IODP JRSO.
JOURNAL
Science
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Ultra-low frictional healing explains recurring slow slip events
ARTICLE PUBLICATION DATE
17-Feb-2023
Slow motion: Scientists investigate tectonic plate boundary earthquake behavior
Utah State University geophysicist Srisharan Shreedharan and colleagues publish findings on New Zealand's Hikurangi Plate Boundary in 'Science'
Peer-Reviewed PublicationIMAGE: FROM LEFT, GEOSCIENTISTS ANNIKA GREEVE OF UTRECH UNIVERSITY AND SRISHARAN SHREEDHARAN OF UTAH STATE UNIVERSITY EXAMINE CORE SAMPLES ABOARD THE IODP RESEARCH VESSEL JOIDES RESOLUTION NEAR NEW ZEALAND. SHREEDHARAN AND COLLEAGUES PUBLISHED FINDINGS FROM DATA COLLECTED ON THE OCEAN EXPEDITION IN THE JOURNAL 'SCIENCE' FEB. 17, 2023. view more
CREDIT: IODP TAMU
LOGAN, UTAH, USA - Renaissance polymath Leonard da Vinci demonstrated frictional forces slow down the motion of surfaces in contact. Friction, he determined, is proportional to normal force. When two objects are pressed together twice as hard, friction doubles.
“We see this principle with tectonic plate boundaries,” says Utah State University geophysicist Srisharan Shreedharan. “As surfaces slide against each other, we observe frictional properties, including frictional healing that describes the degree of fault restrengthening between earthquakes. However, we know little about how this phenomenon may affect future slip events, including earthquakes.”
He and colleagues Demian Saffer and Laura Wallace of the University of Texas at Austin, where Shreedharan was previously employed as a postdoctoral fellow, and Charles Williams of New Zealand’s GNS Science geoscience research institute, publish findings about ultralow frictional healing and slow slip events along the Hikurangi tectonic plate boundary in the Feb. 17, 2023 issue of the journal Science. The team’s research was supported by the U.S. Science Support Program International Ocean Discovery Program (IODP) and the New Zealand Ministry of Business, Innovation and Employment Endeavour Research Fund.
“Plate motion on shallow subduction megathrusts, like the Hikurangi Trench east of New Zealand’s North Island, occurs all over the world,” says Shreedharan, assistant professor in USU’s Department of Geosciences. “Our research examined the diverse tectonic slip modes, especially slow slip events, and focused on frictional healing.”
Slow slip events usually don’t cause great shaking and they generally release pent-up energy in a non-damaging way, he says.
“But in areas with clay-rich materials, such as those commonly found in subduction zones throughout the planet, frequent ‘slow motion’ slips may be more common than we think,” Shreedharan says. “We don’t yet know whether these slip events are more or less likely to place nearby populated areas at risk of deadly earthquakes and tsunamis.”
The behavior of the shallowest reaches of subduction zones during an earthquake determine the nature and size of tsunamis, he says. “Our nation’s west coast is vulnerable to large quakes, so it is important to understand how slip occurs on shallow plate boundaries.”
The USU geophysicist spent two months aboard the IODP research vessel JOIDES Resolution with a team of geoscientists and drilling engineers that drilled holes for monitoring sites along the Hikugangi Trench.
“To quantify seismic hazards, you need to collect data from sensors inside the boreholes,” Shreedharan says. “It’s a big undertaking, but the data is critical for monitoring events and Improving early warning systems.”
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JOURNAL
Science
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Ultralow frictional healing explains recurring slow slip events
ARTICLE PUBLICATION DATE
17-Feb-2023
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