Large storms such as the hurricanes and nor’easters that sweep off New England can whip up ocean waves to the point where they pound the sea floor, causing hundreds of underwater earthquakes, or “stormquakes,” a new scientific study suggests.
The study located thousands of the stormquakes over a decade off North America. Some shook the earth more strongly than a 3.5-magnitude earthquake, researchers said in a paper published earlier this month in Geophysical Research Letters.
Researchers found certain hot spots, near the edge of the continental shelf and around ocean banks, said Wenyuan Fan, a geophysics professor at Florida State University who was the lead author of the study.
They aren’t completely sure how the stormquakes are generated, but they believe that large waves interact with the sea bottom in those regions and the interaction produces a “hammering effect.”
“The hammer knocks on the sea floor,” Fan said.
One hot spot for stormquakes is Georges Bank, which is in the ocean east of New England. Another is the Grand Banks off Newfoundland, Fan said.
Fan said no one has probably ever felt a stormquake because they occur so far off the coast — not to mention in areas that are underwater.
The research team, which also included scientists from the US Geological Survey, the Woods Hole Oceanographic Institution, and the Scripps Institution of Oceanography, analyzed seismic data and detected stormquakes off of North America’s east and west coasts as well as in the Gulf of Mexico.
The necessary conditions for stormquakes are not found off every coast, but there are other areas of the world where they also may be occurring, researchers said.
“Our observations suggest that large continental shelves, ocean banks, and strong storms are the three factors that are necessary for the generation of stormquakes. If this holds true, we would also expect intense stormquake activity offshore Western Europe and offshore northern Australia,” the study said.
One example highlighted by researchers was Hurricane Bill, which steamed off the coast of Massachusetts in August 2009.
High waves and surf kept people out of the water from the North Shore to Nantucket for two days, though little damage was reported on the coast, the Globe reported at the time. The storm turned tragic farther north when a 7-year-old girl was swept to her death in front of thousands who had gathered to watch the storm at Acadia National Park in Maine.
Out in the ocean, something else was going on. The storm generated almost 300 stormquakes within 30 hours, Fan said. Vibrations from stormquakes at one point on Aug. 23 were clearly recorded by stations nearly 2,500 miles away.
“The located seismic sources robustly correlate with the leading edge of the storm track,” the study said.
Noting that no ordinary earthquakes were detected in the region, the study said, “Without any other indigenous source or other energy influx in the region during the passage of Hurricane Bill, our observations strongly suggest that the located seismic sources were excited by this hurricane.”
The idea that there is a connection between the sloshing of the ocean and the vibration of the earth detected by seismologists is not new, Fan said.
He said the new research takes a step forward because researchers were able to pinpoint the sources of the vibrations.
He said the “really exciting part” is that people had previously tended to think of the ocean-earth interaction as a “random process” and the seismic signals during storms as “noise” originating from undetermined locations.
“Now we can be deterministic. It’s not necessarily completely random. It’s a real seismic signal. It’s not noise anymore, since we know what’s producing it and where it’s from,” he said.
John E. Ebel, a senior research scientist at the Weston Observatory at Boston College, said the researchers, in using data from a new seismic detection network called the USArray Transportable Array, had underlined the network’s exciting potential.
The Transportable Array has been placing 1,000 seismic stations in the field, within 40 or 50 miles of each other, in various regions around the United States, moving the network periodically to new regions. The network provides much more detailed data than has been collected in the past, he said.
“It’s like using a high-powered microscope to look at the earth,” Ebel said.
Martin Finucane can be reached at firstname.lastname@example.org