Mysterious earthquakes strike like clockwork – we may finally know why: ScienceAlert

For more than three decades, experts have been trying to solve the mystery of why a certain type of underwater fault causes earthquakes in a more predictable way than others.

These earthquakes can occur almost like clockwork, and are always the same size.

A new study offers a possible answer.

These oceanic transform faults, as they are known, are surrounded by buffer zones, which researchers from across the United States and Canada have shown act as natural “brakes” on seismic activity.

The process known as extensional strengthening — which occurs when seawater seeps deep into rock — is what protects these fault sections from the violence of larger earthquakes, the researchers report.

By revealing the secrets of these extraordinarily predictable faults, the hope is that seismic models can be upgraded more generally.

“We’ve known these barriers have been around for a long time, but the question has always been: What are they made of, and why do they continue to reliably stop earthquakes, cycle after cycle?” says seismologist Jianhua Gong, from Indiana University Bloomington in the United States.

The researchers studied data from two sections along the Juvar transform fault, an extended underwater basin that marks the boundary between the Pacific and Nazca tectonic plates, west of Ecuador and in the deep Pacific.

The researchers discovered that barrier zones around the fault can act as a barrier, temporarily stabilizing the rocks. (Jung et al., Science, 2026)

These plates rub against each other at a rate of about 140 millimeters (5.5 inches) per year, and the fault has generated a regular 6-magnitude earthquake every five or six years since complete record-keeping began in 1995.

In two separate experiments, conducted in 2008 and 2019-2022, ocean bottom seismometers (OBS) were placed directly on the sea floor to track movement. These instruments captured details of tens of thousands of small earthquakes around two large earthquakes.

Data analysis showed that the two parts of the Govar Fault, each with a buffer zone, shook in a similar way. Measurements showed that the barrier zones are actually complex networks of small faults, absorbing the many minor shocks that precede large earthquakes.

When major earthquakes occur, the fluid-filled rocks around these buffer zones move and expand, and more water rushes into the gaps. This creates pressure changes that cause the rocks to “lock” and prevent further sliding, preventing the earthquake from becoming larger.

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“These barriers are not just negative features of the landscape,” says Gong.

“They are active, dynamic parts of the fault system, and understanding how they work changes the way we think about the limits of earthquakes on these faults.”

Seismologists have observed similar scenarios on oceanic transform faults around the world: earthquakes on these faults are smaller than expected, given geological stresses and layout.

While only one specific fault has been analyzed so far in this study, buffer zones such as those surrounding the Govar Fault can overrun other faults as well.

This requires the same type of complex fracturing and seawater infiltration as observed in this study. The researchers suggest that future research could look into this, perhaps using techniques such as drilling into the seafloor.

Due to the location of the Govar Fault, there is no real concern of earthquakes here causing damage to built-up areas or loss of life. However, these results may provide new insight into potentially more dangerous earthquake zones.

Earthquakes caused by most faults other than oceanic transform faults – whether under the ocean or on land – are notoriously unpredictable, but every step forward in scientific understanding brings us closer to knowing when and where earthquakes will strike.

RELATED: How a giant earthquake caused a surprisingly small tsunami

“The predictable seismic cycles and spatially confined rupture zones documented in the 2008 and 2020 OBS experiments demonstrate that targeted, multi-year deployments are necessary to capture seismic details associated with large oceanic transform fault earthquakes and resolve their underlying mechanisms,” the researchers wrote in their published paper.

“Such observations yield new insights into earthquake physics and provide powerful constraints for numerical models.”

The research was published in Science magazine.

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