Scientists Discover How Tides Can Trigger Earthquakes

(CN) – Seismologists examining the ebb and flow of tremors at one of the deepest points of the Pacific Ocean said in a study published Friday that both tidal currents and fracking operations are triggering earthquakes along underwater mountain ranges.

For years now, scientists have understood the link between deep ocean earthquakes and tides, but they remained confounded by the paradoxical spike in tremors when tides were low, explained seismologist Christopher Scholz of Columbia University.

“Everyone was sort of stumped,” Scholz said in a statement. “Because according to conventional theory, those earthquakes should occur at high tides.”

Scientists believed that at high tide, the large volume of water resting on the highest point of a deep ocean fault – which Scholz describes as tilted planes meeting and separating massive blocks of earth – would drive the upper block down and trigger a quake.  

But that’s not what happens. The upward pull of low tide currents drives faults down, “which is the opposite of what you’d expect,” said Scholz, adding that the findings further clouded seismologists’ understandings of how quakes were triggered.

Scholz and his colleagues from the University of Bristol then set off to the Juan de Fuca Ridge in the Pacific Ocean – a 300-mile underwater volcanic range off the coast of Oregon – where they examined the Axial volcano.

The team then used data from a network of seismic monitors around the volcano, which erupts every 10 years or so, to determine how low tides could be causing the tremors.

In a study published Friday in scientific journal Nature Communications, the researchers said that at Axial, they uncovered the mechanism behind tidally triggered earthquakes.

“It’s the magma chamber breathing, expanding and contracting due to the tides, that’s making the faults move,” said Scholz, who co-led the study along with Columbia University student Yen Joe Tan.

Axial’s magma chamber, the soft, pressurized pocket below the volcano’s surface, expanded during low tides when less water was above it, the scientists found.

When the chamber expanded, it moved the rocks around it, causing the lower block of the fault to slide up and trigger an earthquake.

Researchers said that even the tiniest stress on the deep ocean fault – such as seismic waves from another earthquake or tremors from fracking wastewater being pumped into the ground – could trigger a quake.

“People in the hydrofracking business want to know, is there some safe pressure you can pump and make sure you don’t produce any earthquakes?” Scholz said. “And the answer that we find is that there isn’t any – it can happen at any level of stress.”

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