Tides Tied to Undersea Quakes

Whole lotta shakin'. An underwater map of Axial Volcano, showing earthquakes (green) and instruments for recording tides and earthquakes (yellow).

The ebb and flow of ocean tides may play a role in triggering earthquakes. For the first time, geophysicists have discovered a link between the tides and small earthquakes near an undersea volcano in the Pacific Ocean. The correlation may be essential to organisms living on the sea floor, the researchers say.

Scientists have been hunting for a correlation between tidal forces on land and earthquakes for more than 20 years, but couldn't find a pattern. Taking the hunt offshore, researchers led by Maya Tolstoy of the Lamont-Doherty Earth Observatory at Columbia University in New York City placed seismometers to record earthquakes coupled with supersensitive tiltmeters to measure ocean tides on the summit caldera of Axial Volcano on the Juan de Fuca Ridge, several hundred kilometers off the coast of Oregon. Over the 2-month experiment, the instruments recorded more than 400 earthquakes with magnitudes less than 2.5, the team reports in the June issue of Geology. Tolstoy and her colleagues found that significantly more tremors occurred during low tide.

The reason, Tolstoy suggests, is that faults can slip more easily when less water is weighing them down. The lightened load may also let sea-floor cracks open enough for water to trickle in, lubricating the faults and encouraging them to slip. At high tide, the water would be squeezed out. This pumping effect could help marine life by releasing nutrients in the rocks. Once freed, the nutrients may rise toward the surface with water superheated by the Axial Volcano. In effect, the earthquakes may be controlling the flow of nutrients to creatures on the sea floor, says Tolstoy.

And there may be a lot of life below the sea floor that depends on the fluids flowing within the rocks, says Paul Johnson, a marine geologist at the University of Washington, Seattle. "The fact that you can actually change fluid circulation in the crustal rocks with tides to the point where you are breaking rock is serious stuff. Now we're going to have to show the chemists and biologists that this is an important phenomenon." The subsurface biosphere may be where life on this planet originated, says Tolstoy, and it could provide a model of life on other planets.

Related sites
Lamont-Doherty Earth Observatory of Columbia University
Maya Tolstoy's home page
University of Washington School of Oceanography
Axial Volcano's 1998 eruption

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