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Superstorm Sandy Shook the U. S., Literally
Friday, April 19, 2013 1:18
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Apr. 18, 2013 — When superstorm Sandy turned and took aim at New York City and Long Island last October, ocean waves hitting each other and the shore rattled the seafloor and much of the United States — shaking detected by seismometers across the country, University of Utah researchers found.
“We detected seismic waves created by the oceans waves both hitting the East Coast and smashing into each other,” with the most intense seismic activity recorded when Sandy turned toward Long Island, New York and New Jersey, says Keith Koper, director of the University of Utah Seismograph Stations.
“We were able to track the hurricane by looking at the ‘microseisms’ [relatively small seismic waves] generated by Sandy,” says Oner Sufri, a University of Utah geology and geophysics doctoral student and first author of the study with Koper. “As the storm turned west-northwest, the seismometers lit up.”
Sufri was scheduled to present the preliminary, unpublished findings in Salt Lake City Thursday, April 18 during the Seismological Society of America’s annual meeting.
There is no magnitude scale for the microseisms generated by Sandy, but Koper says they range from roughly 2 to 3 on a quake magnitude scale. The conversion is difficult because earthquakes pack a quick punch, while storms unleash their energy for many hours.
The shaking was caused partly by waves hitting the East Coast, but much more by waves colliding with other waves in the ocean, setting up “standing waves” that reach the seafloor and transmit energy to it, Sufri and Koper say.
While many people may not realize it, earthquakes are not the only events that generate seismic waves. So do mining and mine collapses; storm winds, waves and tornadoes; traffic, construction and other urban activities; and meteors hitting Earth.
“They are not earthquakes; they are seismic waves,” says Koper, a seismologist and associate professor of geology and geophysics. “Seismic waves can be created by a range of causes. … We have beautiful seismic records of the meteor that hit Russia. That’s not an earthquake, but it created ground motion.”
While Sandy’s seismicity may be news to many, Koper says microseisms just as strong were detected before and after the superstorm from North Pacific and North Atlantic storms that never hit land but created “serious ocean wave action.”
Koper adds: “Hurricane Katrina in 2005 was recorded by a seismic array in California, and they could track the path of the storm remotely using seismometers.”
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