Scientists Narrow Link Between Tides and Earthquakes

The link between undersea earthquakes and tides has long been known, but it wasn't clear why low tides seem to be a trigger for temblors.

“Everyone was sort of stumped, because according to conventional theory, those earthquakes should occur at high tides,” Christopher Scholz, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory, said in a press release.

Now, Scholz and a team of fellow researchers think they have the answer.

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In a study published recently in Nature Communications, the researchers found that the specific way low tides cause the magma below mid-ocean ridges to move faults is what triggers earthquakes.

Scholz described a mid-ocean fault as "a tilted plane that separates two blocks of earth." When it moves, the upper block slides down.

“It’s the magma chamber breathing, expanding and contracting due to the tides that’s making the faults move,” Scholz said in the press release.

The research team studied the underwater Axial Volcano along the Juan de Fuca Ridge. The type of quakes they focused on are small and aren't felt on land, Scholz said. The volcano is about 300 miles off the coast of Oregon, but sits nearly 4,600 miles below the surface of the Pacific Ocean, according to NOAA.

The area is a good study site because the volcano erupts every decade or so, and scientists have set up a vast network of underwater instruments to monitor it. The last time it erupted was 2015.

“It turned out that this particular place is the most sensitive place we’ve ever seen on earth (to track tides),” Scholz said in an interview with weather.com.

Scholz said the research also showed that even the tiniest stress on a fault could set an earthquake in motion, and the amount of stress that leads to a quake varies. That conclusion, he added, is important when discussing potential earthquake triggers like disposal of wastewater from fracking, which is pumped deep underground.

"Is there a threshold level of stress to trigger an earthquake? What we’ve found is there isn’t any safe pressure," Scholz said. "The threshold is zero.”