 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."
On 29 August 2005, as hurricane Katrina was rumbling towards New Orleans, a seismic hum more than 1000 times the strength of the average volcanic tremor was felt nearly 3000 kilometers away in southern California. Its source was the hurricane itself.
Hurricanes create large ocean waves, which send energy pulsing through the Earth as they pound the shoreline. To determine the power of Katrina's seismic waves, Peter Gerstoft of the University of California, San Diego, and colleagues analyzed the signals recorded by a network of 150 seismic stations in southern California just before Katrina hit the Louisiana coast.
In a related study set for presentation on Friday at the seismology meeting, Koper and geophysics undergraduate student YeouHui Wong found preliminary evidence that seismometers near Utah’s Great Salt Lake are picking up seismic waves generated either by waves or winds on the lake.
Sufri says the new study included Earthscope data from Oct. 18 to Nov. 3, 2012, "which coincides with the passage of Hurricane Sandy, and we tried to understand microseisms that were generated."
Sandy caused a damaging storm surge due to its size — almost 1,100 miles in diameter for tropical-storm-force winds — more than its intensity, which was 3 when it hit Cuba and 2 off the Northeast coast.
Normal ocean waves "decay with depth very quickly," says Koper. But when Sandy turned, there was a sudden increase in waves hitting waves to create "standing waves" like those created when you throw two pebbles in a pond and the ripples intersect.
Seismologists can track Sandy and other big storms because seismometers detect three components of motion: one vertical and two horizontal. If most of the energy on a seismometer is detected with a north-south motion, it means the source of the energy is north or south of the device.
"If you have enough seismometers, you can get enough data to get arrows to point at the source," Koper says.
He says the seismologists didn’t track Sandy in real time, but the seismographic data of the storm suggests it might be possible to help track storms in the future using their seismicity.
For further information see Sandy Seismic Waves.
Seismic Map image by Keith Koper, University of Utah Seismograph Stations