Juan de Fuca Plate Is the Single Greatest Geophysical Hazard to the U.S.

Because the Juan de Fuca plate represents the single greatest geophysical hazard to the continental United States, scientists are keen to learn more. 
 (Image:  Coco et Jo via flickr  /  CC BY-SA 2.0)
Because the Juan de Fuca plate represents the single greatest geophysical hazard to the continental United States, scientists are keen to learn more. (Image: Coco et Jo via flickr / CC BY-SA 2.0)

The Juan de Fuca is a small tectonic plate that sits several hundred miles off the Pacific Northwest coast. But it is potentially a perfect storm it slowly slides under the North American continent with the potential to generate massive earthquakes with accompanying tsunamis.

Because the Juan de Fuca plate represents the single greatest geophysical hazard to the continental United States, scientists are keen to learn more about it. It is understood that quakes from this area could be hundreds of times more damaging than a big quake from the San Andreas Fault.

Subduction process of the Juan de Fuca Plate in Oregon, USA as a cutaway graphic. (Image: via U.S. Geological Survey (USGS))

Subduction process of the Juan de Fuca Plate in Oregon, U.S. as a cutaway graphic. (Image: U.S. Geological Survey (USGS))

The Juan de Fuca plate started its life 300 miles off the coast, along a lengthy range of underwater volcanoes that are producing new crusts deep below the sea. This area is part of the global mid-ocean ridge system that encircles the planet — it is these regions where 70 percent of the Earth’s tectonic plates are generated.

Ocean-bottom seismometers aboard the R/V Welcoma were deployed in the first year of the Cascadia Initiative. (Image: via DAVE O'GORMAN)

Ocean-bottom seismometers aboard the R/V Welcoma were deployed in the first year of the Cascadia Initiative. (Image: DAVE O’GORMAN)

Scientists have struggled to understand these chains of volcanoes as they lie more than a mile beneath the sea surface. However, using an unusual measurement technique, geophysicist Zachary Eilon and his co-author of the paper Geoff Abers have found seismic attenuation, or energy loss, at the mid-ocean ridge where the Juan de Fuca Plate was created.

The geophysicist’s data indicates that molten rock here is found deeper within the Earth than scientists had previously thought. Knowing this will help scientists understand how the Earth’s tectonic plates are built, as well as the deep volcanic systems. Eilon said in a statement:

In their paper, the researchers have calculated that in the narrow strip underneath the mid-ocean ridge, there is very high attenuation, where hot rock wells up to generate the Juan de Fuca Plate. Going further, they state that the levels are as high as scientists have seen anywhere on the planet.

It was also found that the plate is cooling much faster than expected. This affects the friction at the collision zone and the size of any potential megaquake (seismic waves begin at an earthquake and radiate away from it).

While traveling through the water, they lose energy. Some of the loss is due to the wave spreading out; however, there is another factor that also affects energy loss. It’s called the quality factor. To explain this factor, Eilon uses the analogy of a bell, saying:

Attenuation values recorded at ocean-bottom stations. Radial spokes show individual arrivals at their incoming azimuth; central circles show averages at each station. (Image: via DAVE O'GORMAN)

Attenuation values recorded at ocean-bottom stations. Radial spokes show individual arrivals at their incoming azimuth; central circles show averages at each station. (Image: DAVE O’GORMAN)

The researchers observed the way different frequencies of seismic waves attenuated at different rates. Eilon explained:

Next year, there will be an international effort from researchers, including Eilon, to instrumentize large unexplored areas of the Pacific with ocean bottom seismometers. After all the data has been collected, Eilon, using the same techniques he used on the Juan de Fuca, hopes to learn more about what it truly lying beneath the seafloor. Eilon explained that:

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