Giant earthquakes can form at low-angle fault planes, contradicting previous theories

A research team led by Satoshi Ide from the University of Tokyo has revealed that giant earthquakes can occur at low-angle fault planes, a finding published on July 1, 2026, in Science Advances. This discovery challenges traditional earthquake generation theories that suggest such conditions are not conducive to large seismic events.

Understanding the Formation of Giant Earthquakes

Earthquakes are the Earth's mechanism for relieving stress built up between tectonic plates. As these plates move past each other, friction causes stress to accumulate until it is released as seismic waves, leading to destruction. Despite classic theories, which state that low-angle faults are not optimal for giant earthquakes, Ide's research indicates otherwise.

“Giant earthquakes have often been observed near low-angle faults,” Ide stated. “But according to classic theory, the conditions are actually not optimal for giant earthquakes to form in these areas, leaving their formation unexplained.” This insight opens new avenues for monitoring potential earthquake regions.

Statistical Clues and Fault Angles

The research team analyzed a global catalog of earthquakes from 1976 to 2024 to identify patterns in earthquake growth probabilities, known as the b-value. This statistic reflects the ratio of small to large earthquakes in a region. A lower b-value indicates a higher likelihood of significant earthquakes.

• The catalog analysis showed:
• Low dip angle fault planes frequently exhibited low b-values.
• This suggests a greater probability for large earthquakes in these areas.

Ide remarked, “Given that these catalogs are standard rather than exceptional, it is surprising that such a clear relationship between earthquake growth probability and fault dip angle has previously been overlooked.”

Resolving the Contradiction with Stress Orientation

To address the contradiction with the established Andersonian fault theory, which posits insufficient stress at low dip angles for giant earthquakes, the researchers examined the orientation of the stress field. Their calculations indicated that under optimal stress orientations, sufficient energy could be generated for giant earthquakes to form.

“Our findings underscore the critical importance of tectonic stress orientation. Monitoring stress orientation in potential future earthquake regions will significantly improve the probabilistic forecasting of giant earthquakes,” Ide added.