An undersea fault deep in the eastern Pacific Ocean, about 1,000 miles west of Ecuador, has been producing magnitude 6 earthquakes with alarming regularity for at least 30 years. Earthquakes occur approximately every five to six years, rupturing roughly the same part of a fault repeatedly and reaching roughly the same magnitude.
Such consistency is extremely rare in earthquake science, and researchers have long struggled to explain how the pattern continues so reliably.
Now, scientists say they’ve finally identified the reason. New research published in journal science It turns out that special areas within the fault itself act as a natural braking system that repeatedly stops earthquakes from growing larger.
“We’ve known for a long time that these barriers exist, but the question has always been: What are they made of, and why do they continue to stop earthquakes so reliably, time and time again?” said seismologist Jian Hua Gong, lead author of the study and assistant professor of Earth and Atmospheric Sciences in Indiana University Bloomington’s College of Arts and Sciences.
Gong collaborated with researchers at Woods Hole Oceanographic Institution, Scripps Institution of Oceanography at the University of California, San Diego, U.S. Geological Survey, Boston College, University of Delaware, Western Washington University, University of New Hampshire, and McGill University. Together, they focused on the Goffal transform fault, located along the East Pacific Rise off the west coast of Ecuador, to solve the decades-old mystery surrounding these recurring undersea earthquakes.
Goffal fault and repeated earthquakes
The Gofar Fault is a deep undersea fault where the Pacific and Nazca plates slide against each other at a rate of about 140 millimeters per year, which is about as fast as a fingernail can grow. Transform faults are regions where tectonic plates move horizontally alongside each other, making Gofar one of the best-studied examples on the ocean floor.
What makes this fault particularly unusual is that larger earthquakes continue to occur and stop in roughly the same location. Between the sections where large earthquakes occur, there are stretches of quiet faults that appear to absorb stress without causing major rupture. Scientists refer to these regions as “barriers,” but until now their exact role has remained unclear.
For their study, the researchers used information collected from two large-scale undersea experiments conducted in 2008 and 2019-2022. During these missions, scientists installed submarine seismometers, instruments designed to directly detect earthquakes on the ocean floor, along two sections of the Ghofar Fault.
The instrument captured tens of thousands of small earthquakes that occurred before and after two large magnitude 6 events. This allowed the researchers to observe in great detail how faults behaved leading up to, during, and after large-scale ruptures.
“Barrier zone” hidden deep under the sea
The research team found surprisingly similar patterns in both barrier regions. In the days and weeks before the major earthquake, the barrier zone experienced a burst of small-scale seismic activity. Immediately after the larger earthquake, the same area became almost completely silent.
Because the phenomenon occurred on two separate fault segments studied 12 years apart, the researchers concluded that the same physical process was responsible in both cases.
Research shows that this barrier is not an inert piece of rock. Rather, it is a highly complex area where the disorder splits into multiple strands. Small lateral offsets of 100 to 400 meters between these strands create local openings within the fault structure, similar to small gaps within fractures.
The researchers also found evidence that seawater is seeping deep into these fracture zones. The unusual shape and trapped fluid combine to create conditions for a process called “dilatancy enhancement.”
Mechanism of the “brake” of natural earthquakes
During a major earthquake, the sudden movement along a fault causes the pressure inside the fluid-filled rock to drop rapidly. When that happens, the porous rock becomes temporarily locked, slowing or stopping the destruction before it continues to spread and grow.
In fact, the barrier zone acts like a brake built into the fault.
“These barriers are not just passive features of the landscape,” Gong explained. “They are active, dynamic parts of fault systems, and understanding how they function changes the way we think about the seismic limits of these faults.”
Because the Goffal Fault is far from populated coastlines, the earthquake itself poses little direct threat to people. But this discovery could have far broader implications for earthquake science around the world.
Impact on earthquake prediction
Transforming faults similar to Gofar have been found throughout Earth’s oceans. Scientists have long noticed that underwater earthquakes along these faults often remain smaller than geological conditions allow, as if their maximum magnitude is limited by natural mechanisms.
A new study suggests barrier zones like the one found on Goffal may be common throughout the ocean floor. If so, they could act as a widespread system of natural seismic brakes that prevent some ruptures from escalating into even larger events.
Researchers say the discovery could improve earthquake models used to estimate seismic risk along submarine faults around the world, including in areas near major coastal populations.
This research was funded by the U.S. National Science Foundation and the Natural Sciences and Engineering Research Council of Canada.
