Scientists study the seismic behavior of the tectonic plate boundary

Renaissance polymath Leonardo da Vinci demonstrated that frictional forces slow the movement of surfaces in contact. Friction, he found, is proportional to normal force. When two objects are pressed together twice as hard, the friction doubles.

“We see this principle at tectonic plate boundaries,” says geophysicist Srisharan Shreedharan of Utah State University. “When surfaces slide against each other, we observe frictional properties, including frictional healing, which describe the degree of fault resolidification between earthquakes. However, we know little about how this phenomenon might affect future sliding events, including earthquakes.”

He and his colleagues Demian Saffer and Laura Wallace from the University of Texas at Austin, where Shreedharan was previously a postdoctoral fellow, and Charles Williams from the New Zealand geoscientific research institute GNS Science publish results on ultra-low friction healing and slow slip events along the Hikurangi tectonic plate boundary in the February 17, 2023 issue of the magazine Science.

“Plate motions in shallow subduction megathrusts, like the Hikurangi Trench east of New Zealand’s North Island, occur all over the world,” says Shreedharan, an assistant professor in USU’s Department of Geosciences. “Our research examined the different tectonic slip modes, particularly slow slip events, and focused on friction healing.”

Slow-slip events don’t typically cause large shocks and generally release pent-up energy in a nondamaging way, he says.

“But in areas of argillaceous material, such as those commonly found in subduction zones across the planet, frequent slow-motion slips may be more common than we think,” says Shreedharan. “We don’t yet know whether these slip events are more or less likely to put nearby populated areas at risk of deadly earthquakes and tsunamis.”

The behavior of the shallowest areas of subduction zones during an earthquake determines the type and size of tsunamis, he says. “Our country’s west coast is prone to large earthquakes, so it’s important to understand how slip occurs at shallow plate boundaries.”

The USU geophysicist spent two months aboard the IODP research vessel JOIDES Resolution with a team of geoscientists and drilling engineers drilling holes for monitoring sites along the Hikugangi Trench.

“To quantify seismic hazards, you need to collect data from downhole sensors,” says Shreedharan. “It’s a big undertaking, but the data is critical to monitoring events and improving early warning systems.”