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'Stormquakes' under ocean waves are spurred by hurricanes, researchers say

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The eye of Hurricane Dorian evolved to a Category 5 hurricane. Shown from the International Space Station. File/NASA/AP

Scientists have discovered a new phenomenon tied to hurricanes — "stormquakes," or shaking of the ocean floor during a strong enough storm. 

The shaking, which has been tied to both tropical cyclones and nor'easters, was outlined in a paper published earlier this year in Geophysical Research Letters. Wenyuan Fan, a professor at Florida State University, led a team of researchers in uncovering the previously unknown underwater quakes. 

Already, powerful swirling storms transfer energy from the atmosphere to ocean water, kicking up swells that become storm surge when they reach land. In some cases, the energy in the ocean is then transmitted into the solid earth as broad waves move across continental shelves, Fan said. 

The shaking can be as powerful as a magnitude 3.5 earthquake and happen over an area 35 to 60 miles wide. On land, that amount of shaking would be noticeable but would likely cause only minor damage. A temblor of that magnitude in Los Angeles earlier this year didn't significantly harm any structures, the Los Angeles Times reported

The phenomenon Fan and his colleagues have described under the ocean is novel and still little-understood. Previously it was mistaken for "seismic ambient noise," or a low-level humming of the Earth's crust that scientists first described decades ago, even without an earthquake.

There are certain hotspots where stormquakes tend to occur but scientists are not sure why. The closest to South Carolina is a long corridor northeast of the Bahamas and Turks and Caicos. Data points showing the quakes in that area form a line that is parallel to the slant of the island chain. 

Hurricane Wire is a pop-up newsletter during hurricane season that delivers anyone who lives on the East Coast all the information they need to know as storms brew in the Atlantic and beyond.

Fan and his colleagues have hypothesized that ocean floor topography has something to do with where the shaking happens. They also don't know the exact mechanism by which storm waves actually make the ground shake. 

Stormquakes have also only been detected in relatively shallow ocean waters. Researchers analyzed 10 years of data from a network of movable seismographs to pinpoint the temblors. 

"We have not observed stormquakes outside of continental shelves," Fan said. 

It's possible that in future study, Fan's team or other researchers could use another new technology from this year to listen more closely to the quakes beneath the waves. Researchers from Lawrence Berkeley National Laboratory published a paper on how they employed unused fiber optic cable to detect seismic activity. 

That development was a promising one, Fan said, but wasn't ready quite yet to detect stormquakes. The fiber optic cables have mostly been used to track horizontal shaking, while the ground moves mostly in a vertical motion during a stormquake. 

"With continuous development, I am sure that the (fiber cable) data will be a valuable resource to understand the phenomenon," Fan said. 

Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.

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