20 October, 2019
Scientists say they have discovered an earthquake-like event that can happen during a hurricane or other powerful ocean storms. They are calling it a "stormquake."
Researchers came up with this name after studying seismic events on the sea floor during such storms. They found that the shaking can last for several days and feel as strong as a magnitude 3.5 earthquake.
The discovery was made by a research team led by Wenyuan Fan, a seismologist and professor at Florida State University. His team examined seismic and ocean records from September 2006 to early 2019 in an effort to identify possible stormquakes.
A report on the study was published in Geophysical Research Letters.
Intense energy from hurricanes and other severe storms can create very large waves in the ocean. These waves then "interact" in some places with solid earth under the sea to cause "intense seismic source activity," Fan said.
"We can have seismic sources in the ocean just like earthquakes within the crust," he added. "The exciting part is seismic sources caused by hurricanes can last from hours to days."
The researchers found evidence of more than 10,000 stormquakes between 2006 and 2019 in coastal areas of the United States and Canada. Seismic activity was recorded off the coast of New England, as well as off of Florida and in the Gulf of Mexico. In Canada, evidence was found off the eastern provinces of Nova Scotia and Newfoundland, as well as British Columbia's Pacific coast.
Stormquakes were found to have happened around continental shelves or sea floors containing flat land and at lower depths, the research showed.
The researchers considered other weather conditions when they tried to identify whether a seismic event could have been a stormquake. The seismic activity had to happen on a stormy day or have some other connection to a storm. Other seismic events, such as earthquakes, had to be ruled out as causes.
Even with evidence of so many stromquakes happening, it was not known until recently that such events even existed. This is mainly because scientists studying earthquakes have generally considered ocean-caused seismic waves as "background noise."
The research found that major U.S. hurricanes had produced a lot of stormquakes. One example was Hurricane Bill, a storm that formed 10 years ago in the Atlantic Ocean. Bill strengthened into a Category 4 hurricane before weakening to a tropical storm and hitting Newfoundland. The researchers said the storm caused "numerous seismic events" off the northeast U.S. and Canadian coasts.
Other examples of stormquakes were 2008's Hurricane Ike and Hurricane Irene in 2011. Ike led to stormquake activity in the Gulf of Mexico, while Irene caused seismic events off the coast of southern Florida.
The researchers noted that not all hurricanes produce stormquakes. For example, the study found no evidence of stormquakes off the coast of Mexico. Also, no such activity was recorded in areas along the U.S. East Coast, starting in New Jersey, and continuing all the way down to Georgia.
The team noted that even Hurricane Sandy, one of the most costly storms in U.S. history, did not cause a single stormquake. Wenyuan Fan says this suggests that stormquakes are strongly influenced by the physical shape of the seafloor's surface and seafloor conditions.
Fan added that there are still "lots of unknowns" about stormquakes. But he said discovering them "suggests we are reaching a new level of understanding of seismic waves."
Fan said that he hopes the discovery will also lead to improved study methods for hurricanes, which in the past have mainly been observed from satellites in the sky.
"Now we are able to understand the phenomenon – or at least track part of its passage – through the solid earth as well," he said.
I'm Bryan Lynn.
Bryan Lynn wrote this story for VOA Learning English, based on reports from The Associated Press, Florida State University and Geophysical Research Letters. George Grow was the editor.
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Words in This Story
magnitude – n. the size of something; the strength of an earthquake's power
interact – v. act in such a way as to have an effect on something or someone else
source – n. a person, place or thing from which something comes
crust – n. hard, outer surface of something
exciting – adj. producing strong feelings
continental shelf – n. an area at the bottom of the sea near the coast of a continent, where the sea is not very deep
phenomenon – n. someone or something that is popular, especially because of an unusual ability or quality
track – v. to follow the progress of something