‘Standing Waves’ From Superstorm Sandy Caused Seismicity As Far As Seattle

May 20, 2013- When Superstorm Sandy turned toward New York City and Long Island last October, ocean waves hitting each other and the shore rattled the seafloor, with 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, said 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,” said 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.”

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 said.

Earthquakes are not the only events that generate seismic waves. Other events that cause seismic waves include mining and mine collapses, storm winds, waves and tornadoes, construction and other urban activities.

The microseisms generated by Sandy were detected by Earthscope, a National Science Foundation-funded array of about 500 portable seismometers that were first placed in California in 2004 and have been leapfrogging eastward throughout the U.S.

Earthscope’s purpose is to use seismic waves from quakes and other sources to make images of Earth’s crust and upper mantle beneath North America – similar to how X-rays are used to make CT scans of the human body.

“The energy generated by Sandy is going to be used to image the crust and upper mantle under North America,” says Koper, noting that Earthscope uses years of seismic data to construct images. “We are using seismic waves created by ocean waves to make images of the continent.”

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