'Stormquakes': Scientists discover new phenomenon where storms or hurricanes cause earthquake-like seismic activity
Intense storms or hurricanes can produce vibrations in nearby ocean floors as strong as a magnitude 3.5 earthquake, as per scientists, who have dubbed the new phenomenon as "stormquakes."
According to Wenyuan Fan, an assistant professor of Earth, Ocean, and Atmospheric Science at Florida State University and lead author of the study, not all hurricanes cause stormquakes, but when they do, the stormquakes seem to be concentrated in certain hotspots.
"Not every storm can produce stormquakes. Stormquake excitation depends upon the storm strength, storm track, and the local seafloor topography," Fan told MEA WorldWide (MEAWW).
The research team analyzed nearly a decade of seismic and oceanographic records from September 2006 to February 2019 and found a connection between strong storms and intense seismic activity - vibrations in Earth's crust - near the edge of continental shelves or ocean banks.
"Large storms such as hurricanes and Nor' easters generate strong long-period ocean waves, which can interact with shallow seafloor features located near the edge of continental shelves known as ocean banks. Such interactions produce seismic sources with equivalent earthquake magnitudes that can be greater than 3.5. These seismic sources are termed "stormquakes," and they can excite coherent seismic wavefields that are well recorded across the North American continent. Stormquake is a newly identified geophysical phenomenon, which involves interactions of the atmosphere, ocean, and the solid Earth," says the study published in American Geophysical Union or AGU’s Geophysical Research Letters.
The researchers found evidence of more than 10,000 stormquakes occurring from 2006 to 2019 offshore of New England, Florida, and the Gulf of Mexico in the US, as well as offshore of Nova Scotia, Newfoundland, and British Columbia in Canada.
According to scientists, stormquakes can provide useful information to investigate the Earth's structure and ocean wave dynamics. The stormquakes, explain experts, provide new sources to investigate Earth's structure in offshore locations that typically lack both seismic stations and earthquakes. Further, the discovery of stormquakes, says the study, might relate to or can explain previously reported mysterious seismic noise sources near Europe, North America, and Africa.
"Intellectually, the implications are the ocean wave excitation conditions and the coupling between the ocean and the Earth. The type of ocean waves, infragravity waves, that might be responsible to excite stormquakes were previously thought to be strong near the coast, but not at the edge of continental shelves," Fan told MEAWW.
He further explains, "Here, our results show that they can be very strong at the excitation site due to the extreme weather conditions. The results also show that the atmosphere-ocean-solid Earth coupling can happen at particular regions with great strength. This is the opposite of what we used to think about such interactions. For societal relevance, we do not fully understand the connections yet. This is the first study of such phenomena, and I expect there will be more broad implications to be identified."
The research team developed a new method to detect and locate seismic events and determine whether such events are stormquakes. They found that the 2009 Hurricane Bill, which made landfall on Newfoundland on August 22, produced many stormquakes off the coasts of New England and Nova Scotia. Similarly, Hurricane Ike in 2008 caused stormquake activity in the Gulf of Mexico, and Hurricane Irene in 2011 did the same near Little Bahama Bank, off the coast of Florida.
The analysis shows that not all hurricanes cause stormquakes. The researchers did not find any evidence of stormquakes off the coast of Mexico or along the US East Coast from New Jersey to Georgia. Even Hurricane Sandy, one of the costliest storms on record in the US, did not spur stormquakes, says the team, adding that this suggests stormquakes are strongly influenced by the local oceanographic features and seafloor topography.
According to Fan, compared to the storms, stormquakes are quite harmless. They do not generate strong ground motions inland. "However, we have found only regions that have large continental shelves with ocean banks are prone to generate stormquakes. With more extreme storms, one would expect to have more stormquakes. However, the intensity of the stormquakes, (that is, magnitude), is likely to stay stable because that is controlled by the ocean waves and the local seafloor topography," he says.
Fan says further research on the subject is needed as there are still many unknowns. "First, we have speculations about what ocean waves might be responsible for interacting with seafloor topography, but we do not know it for sure. We also do not know the details about how the ocean wave energy is transferred into the solid Earth. In addition to vertical forces, there are horizontal forces present as well, and we do not fully understand why. Finally, we do not know why the observed stormquakes are temporally sporadic at certain regions, but more frequency at others," he told MEAWW.