Ann Arbor Times

On February 26, 2025, a study published in Science Advances sheds new light on the factors contributing to earthquake generation. The research focuses on the properties of rocks within fault zones and their role alongside fault stress in causing earthquakes.

The study, led by Yihe Huang, an associate professor at the University of Michigan, examines data from Japan's eastern Kanto region. This area is notable for its position where the Philippine Sea Plate interacts with both the North American and Pacific Plates. Earthquakes here typically occur at depths between 60 to 70 kilometers and account for about half of those felt in Tokyo.

Huang's team discovered that rock material along this fault line is foliated, meaning minerals are arranged in layers. This structure may significantly influence earthquake generation. "When we think about where earthquakes occur, we are always thinking about a broader scale," Huang explained. "But it’s not like that."

The research suggests that understanding subduction zones' specific active areas could enhance earthquake warning systems. "Our study provides a way for us to find those spots," Huang said.

The findings highlight the anisotropic properties of these rocks, which exhibit varying strengths depending on direction—similar to wood grain characteristics. This unique property results from different rock types mixing along the fault line.

Data was gathered using borehole seismometer stations spaced approximately every 25 kilometers across the region. These instruments allowed researchers to calculate Poisson's ratio, revealing how rocks deform under pressure.

In this case, when squeezed, rocks showed minimal deformation in other directions—a rare observation at this scale according to Huang: "That’s very strange."

Understanding these underlying structures is crucial for predicting earthquakes' occurrence and location. As Huang noted: "Looking at these particular anomalous regions on subduction zones is probably key."

Future research will involve examining ocean floor seismometer data offshore Japan to further investigate rock properties along subduction zone interfaces.