Scientists Finally Solve the Mystery of “Clockwork” Earthquakes

Scientists discovered hidden underwater “brakes” that may keep some earthquakes from becoming catastrophic.

For more than 30 years, a fault line deep beneath the eastern Pacific Ocean has been producing remarkably consistent earthquakes. Located about 1,000 miles off Ecuador’s coast, the underwater fault generates magnitude 6 quakes every five to six years, striking in nearly the same places and with nearly the same strength each time.

That level of regularity is extremely unusual in earthquake science. Researchers have long known about the pattern, but until now they did not fully understand what was causing it.

A new study published in the journal Science has finally uncovered the explanation. Scientists say the fault contains special regions that repeatedly prevent earthquakes from growing larger, acting like natural braking systems deep beneath the seafloor.

“We’ve known these barriers existed for a long time, but the question has always been, what are they made of, and why do they keep stopping earthquakes so reliably, cycle after cycle?” said seismologist Jianhua Gong, lead author of the study and Assistant Professor of Earth and Atmospheric Sciences in the College of Arts and Sciences at Indiana University Bloomington.

Gong and researchers from the Woods Hole Oceanographic Institution, Scripps Institution of Oceanography at UC San Diego, the U.S. Geological Survey, Boston College, the University of Delaware, Western Washington University, the University of New Hampshire, and McGill University focused their work on the Gofar transform fault, part of the East Pacific Rise west of Ecuador. Their goal was to solve a mystery that has puzzled scientists for decades: why some underwater faults produce large earthquakes with almost clocklike timing.

Why the Gofar Fault Is So Unusual

The Gofar fault is a long fracture on the ocean floor where the Pacific and Nazca tectonic plates slide past one another. These giant slabs of Earth’s outer shell move at roughly 140 millimeters per year, about the same speed fingernails grow.

Transform faults form where tectonic plates move horizontally against each other, and Gofar is one of the best-studied examples on Earth’s seafloor.

What makes this fault stand out is the way its larger earthquakes repeatedly begin and end in the same locations. Between the active earthquake zones are quieter sections of the fault that absorb stress without triggering major quakes. Scientists refer to these sections as “barriers,” though their exact function remained unclear for years.

Seafloor Experiments Reveal Hidden Activity

To better understand the fault, researchers analyzed data from two large ocean-floor studies, one performed in 2008 and another conducted from 2019 through 2022.

During both projects, scientists placed ocean bottom seismometers directly on the seafloor along different sections of the Gofar fault. These instruments recorded tens of thousands of small earthquakes occurring before and after two separate magnitude 6 events.

The data provided researchers with an unusually detailed view of how the fault behaves leading up to, during, and after major ruptures.

In both barrier zones, scientists observed nearly identical patterns. Small earthquakes became highly active in the days and weeks before a major quake, then the same regions went almost silent immediately afterward.

Because this behavior appeared in two different fault segments separated by 12 years, researchers concluded that the same physical process was likely responsible in both cases.

Natural “Brakes” Inside the Fault

The study found that the barriers are not simple inactive stretches of rock. Instead, they are structurally complicated regions where the fault breaks into several strands.

These strands are offset sideways by about 100 to 400 meters, creating localized openings in the fault structure, similar to small gaps within a crack.

Researchers also found evidence that seawater penetrates deep into these fractured areas. Together, the fault geometry and trapped fluids create conditions for a process known as “dilatancy strengthening.”

In this process, when a major earthquake rupture reaches one of the barrier zones, sudden movement causes pressure inside the fluid-filled rock to drop sharply. The porous rock then temporarily locks up, slowing or stopping the rupture before it can continue growing.

The result is essentially a natural braking system that limits earthquake size.

“These barriers are not just passive features of the landscape,” Gong explained. “They are active, dynamic parts of the fault system, and understanding how they work changes how we think about earthquake limits on these faults.”

Global Implications for Earthquake Science

Because the Gofar fault lies far from heavily populated coastlines, its earthquakes pose little direct danger to people. However, researchers say the findings could have important implications worldwide.

Transform faults similar to Gofar exist across Earth’s oceans, and scientists have long noticed that many underwater earthquakes remain smaller than expected based on geological conditions alone.

The new research suggests that barrier zones created by complex fault structures and seawater infiltration may be widespread beneath the oceans. If so, these regions could act as natural brakes that limit the maximum size of earthquakes along many underwater faults.

Scientists say the discovery may improve earthquake models used to estimate seismic hazards around the world, including risks near coastal population centers.

Reference: “Predictable seismic cycles result from structural rupture barriers on oceanic transform faults” by Jianhua Gong, Wenyuan Fan, Jeffrey J. McGuire, Mark D. Behn, Jessica M. Warren, Emily Roland, Margaret S. Boettcher, John A. Collins, Yajing Liu and Christopher R. German, 14 May 2026, Science.
DOI: 10.1126/science.ady6190

The research was funded by U.S. the National Science Foundation and Natural Sciences and Engineering Research Council of Canada.

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