Dr. Maya Tolstoy, Associate Research Scientist at the Lamont-Doherty Earth Observatory at Columbia University, is publishing in the June issue of the journal Geology, research showing that earthquakes coming from the Axial Volcano on the Juan de Fuca Ridge, located off the coast of Washington and Oregon, are occurring during tidal lows when the weight of the water is at a minimum. Tolstoy and her colleagues also found a tidal correlation with signals for harmonic tremors, which are thought to result from super heated water moving in the cracks.

The research suggests that the seafloor crust is essentially breathing with the ocean tides, allowing more movement of water through the crust and the release of seismic energy on a regular tidal schedule.

"Scientists have long postulated that earthquakes and tidal movements are somehow connected, but on land the link has been quite difficult to identify. It makes sense that if this correlation were to be seen strongly anywhere, the ocean floor would be the most likely site, since it will be strongly influenced by the tides.

"However, it's only within the last decade that the technology has been available to make the long-term seismic recordings of the seafloor necessary to find this correlation. Our first study on the Axial Volcano began in 1994. Today, we have an interesting and important view into how its deformation, and perhaps the deformation of other underwater volcanoes, works," said Tolstoy.

The Axial Volcano was chosen as a research site because it was thought to be volcanically active. In 1994, Tolstoy and her team deployed equipment on the ocean floor to record both seismic activity and tides. Over a period of two months, 402 micro earthquakes were recorded and they showed both a fortnightly and a diurnal pattern.

It was also recorded that there was a two hour lag between the movement of the tides and the deformation of the Earth's crust, which is a process called an Earth tide. This indicates that the movement of water appears to be a more important force in day-to-day earthquake triggering than the movement of the earth.

In 1998, a major eruption on Axial Volcano occurred. The activity observed in 1994 occurred largely at the site of the 1998 eruption and may have indicated precursory volcanic activity at a site on the brink of an eruption. The existence and timing of the earthquakes is also important in understanding the nutrient supply to the biological communities living in these extreme environments devoid of sunlight.

At the time of the experiment, this research constituted the longest period of continuous recording of seismic activity in a single location. Since then, other longer-term deployments have been made, and similar correlations have been observed in additional locations on the Juan de Fuca Ridge. It is therefore probable that ocean tidal influences are occurring elsewhere on the seafloor and on other mid-ocean ridge chains.

Tolstoy is currently conducting analysis of seismic data from the Mid-Atlantic Ridge to look for similar tidal influences on the seafloor of the Atlantic Ocean.

Dr. Tolstoy is a geophysicist at the Lamont-Doherty Earth Observatory, a research unit for the Columbia Earth Institute. She specializes in the design, execution, and analysis of marine seismic experiments.

In addition to the Juan de Fuca Ridge, she has ongoing research at the Gakkel Ridge, the South East Indian Ridge, the Australian Antarctic Discordance, the East Pacific Rise, and the Mid-Atlantic Ridge.

Tolstoy's paper, "The Breathing of the Seafloor: Tidal correlations of Seismicity at Axial Volcano," is published in the June issue of Geology, the scientific journal of the Geological Society of America.

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