Deep beneath the eastern Pacific Ocean, roughly 1,000 miles west of Ecuador, a seafloor fault has been producing magnitude 6 earthquakes with striking regularity for at least 30 years. The quakes occur about every five to six years, repeatedly rupturing nearly the same sections of the fault and reaching nearly identical magnitudes.
Such consistency is extremely rare in earthquake science, and researchers have long struggled to explain how the pattern could continue so reliably.
Now, scientists say they have finally identified the reason. A new study published in the journal Science reveals that special regions within the fault itself act as natural braking systems that repeatedly stop earthquakes from growing larger.
“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 worked alongside 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. Together, they focused on the Gofar transform fault, located along the East Pacific Rise off Ecuador’s western coast, in an effort to solve a decades-long mystery surrounding these repeating underwater earthquakes.
The Gofar Fault and Its Repeating Earthquakes
The Gofar fault is a deep underwater fracture where the Pacific and Nazca tectonic plates slide past one another at roughly 140 millimeters per year, about as fast as fingernails grow. Transform faults are areas where tectonic plates move horizontally alongside each other, and Gofar has become one of the best studied examples on the ocean floor.
What makes this fault especially unusual is that its larger earthquakes keep starting and stopping in nearly the same locations. Between the sections where major earthquakes occur are quieter stretches of the fault that appear to absorb stress without producing large ruptures. Scientists refer to these areas as “barriers,” but until now, their exact role remained unclear.
To investigate, researchers used information collected during two major seafloor experiments, one carried out in 2008 and another between 2019 and 2022. During these missions, scientists placed ocean bottom seismometers, instruments designed to detect earthquakes directly on the seafloor, along two parts of the Gofar fault.
The instruments captured tens of thousands of tiny earthquakes occurring before and after two major magnitude 6 events. This gave researchers an exceptionally detailed look at how the fault behaves leading up to, during, and after major ruptures.
Hidden “Barrier Zones” Deep Beneath the Ocean
The team discovered a remarkably similar pattern in both barrier regions. In the days and weeks before a major earthquake, the barrier zones experienced bursts of small seismic activity. Immediately after the larger quake occurred, those same regions became almost completely quiet.
Because this behavior appeared in two separate fault segments studied 12 years apart, researchers concluded that the same physical process was responsible in both cases.
According to the study, the barriers are not inactive sections of rock. Instead, they are highly complex areas where the fault breaks into multiple strands. Small sideways offsets between these strands, ranging from 100 to 400 meters, create localized openings within the fault structure, similar to small gaps inside a crack.
Researchers also found evidence that seawater seeps deep into these fractured zones. Together, the unusual geometry and trapped fluids create conditions for a process called “dilatancy strengthening.”
How Natural Earthquake “Brakes” Work
During a large earthquake, sudden movement along the fault causes pressure inside the fluid-filled rock to drop rapidly. As that happens, the porous rock temporarily locks up, slowing or stopping the rupture before it can continue spreading and becoming larger.
In effect, the barrier zones act like built-in brakes inside the fault.
“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.”
The Gofar fault is far from heavily populated coastlines, so the earthquakes themselves pose little direct threat to people. However, the findings may have far broader implications for earthquake science worldwide.
Implications for Earthquake Forecasting
Transform faults similar to Gofar are found throughout Earth’s oceans. Scientists have long noticed that underwater earthquakes along these faults often remain smaller than geological conditions might otherwise permit, as though some natural mechanism limits their maximum size.
The new research suggests that barrier zones like those found at Gofar may be common across the ocean floor. If so, they could function as a widespread system of natural earthquake brakes that prevents some ruptures from escalating into even larger events.
Researchers say the discovery could improve earthquake models used to estimate seismic hazards along underwater faults around the world, including regions closer to major coastal populations.
The research was funded by U.S. the National Science Foundation and Natural Sciences and Engineering Research Council of Canada.