Scientists Discover Hidden 'Brake Zones' That Stop Pacific Earthquakes From Growing Larger

NEWARK, Del. — Scientists studying a remote stretch of the seafloor in the eastern Pacific have identified what appear to be natural "brake zones" inside an undersea fault that stop earthquakes from spreading and growing into much larger events, a finding that could help explain why some of the planet's most predictable quakes have stayed locked into a near-perfect five-to-six-year cycle for at least three decades.

The study, published Thursday in the journal Science, focuses on the Gofar transform fault, a 200-kilometer-long rip in the seafloor roughly 1,000 miles west of Ecuador along the East Pacific Rise. Since the early 1990s the Gofar fault has produced a magnitude 6.0 earthquake every five to six years, almost always rupturing the same patch of crust. That kind of metronomic regularity is virtually unheard of in earthquake science, where most major quakes are stubbornly unpredictable.

Led by Jessica Warren, a geologist at the University of Delaware, the research team deployed a dense network of 50 ocean-bottom seismometers along the Gofar fault between 2008 and 2009 and recorded tens of thousands of micro-earthquakes before, during and after two magnitude 6 ruptures. The pattern that emerged was striking: in the weeks before each big quake, swarms of tiny tremors lit up specific patches along the fault. The moment the larger rupture passed through those same patches, the seismic chatter abruptly fell silent.

The team interprets those quiet patches as structural "barriers" where the fault breaks into multiple anastomosing strands and the surrounding rock is unusually porous and saturated with seawater. When a rupture sweeps in, the sudden movement causes the pore pressure inside the rock to plunge — momentarily wedging the porous matrix shut and halting the rupture before it can grow into something far more destructive. "It's like slamming on the brakes the instant the wheels start to slip," Warren said in a statement.

The Gofar fault is exotic in many ways — it sits beneath three kilometers of seawater and moves twice as fast as California's San Andreas — but the team argues that the brake-zone mechanism it has revealed is unlikely to be unique. "If similar barrier zones exist on other transform faults, including some on land, they may quietly govern the maximum size that earthquakes can reach," said co-author Margaret Boettcher, a seismologist at the University of New Hampshire. Boettcher cautioned that the team has not yet looked for analogous structures on continental faults but said it is "a question worth pursuing aggressively."

Understanding what limits earthquake size has been one of the great open problems in seismology for nearly a century. The discovery comes amid heightened public attention to seismic hazards in the Pacific Northwest, where U.S. Geological Survey models put the chance of a Cascadia subduction-zone megaquake at roughly one in 10 within the next 50 years. The Gofar findings won't change those numbers, the authors said, but they offer the first clear physical explanation of why some of the world's most-watched faults seem to keep their ruptures bounded — and they suggest that what looks like uncannily predictable behavior may, in fact, be the signature of a hidden seismic safety valve.