April 21, 2008 -- Seismologists have discovered a trove of seismic noise from storm surf that provides a new record of global warming's effects on storms.
The pounding of storm waves on any shore creates vibrations in the Earth that can be heard by seismometers and translated into storm power. The archived seismological data now show that this wave energy has been getting stronger for decades, matching what's predicted to happen as the world's oceans and air heat up.
An analysis of decades of digital seismic data at 22 seismic stations worldwide shows that the power of most powerful storm waves is on the rise in every case.
"As I started to plot them my jaw started to drop," said seismologist Rick Aster of the New Mexico Institute of Mining and Technology. Aster presented the results last week at the annual meeting of the Seismological Society of America in Santa Fe, N.M.
For decades the seismic signals from ocean waves was considered mere noise to seismologists. But then researchers like Aster's colleagues Peter Bromirski and Dan McNamara started mining that noise for information.
"We've got a really remarkable record in the seismological community," said Aster.
It's a record developed for entirely different purposes, but now has surprising applications.
The ocean wave effect that is easiest to see in the seismic record is called the global oceanic microseism. This signal is made of seismic waves that take anywhere from 5 to 30 seconds to rise and fall.
"We can see very clearly wave effects," Aster explained.
Seasonal changes in storm tracks, hurricanes and El Niño-driven cyclones are also easy to pick out. Of these, groups of swells striking shorelines can be seen clustered in the seismic charts -- each one spawned by the winds of a particular storm. These signals are particularly clear at coastal seismic stations, but also visible far inland like at a station in Albuquerque, N.M.
"The stations with the most sensitivity are in the North Atlantic and the North Pacific and coastal," said Aster.
Hawaii is the best station of all, since it is surrounded by shorelines and picks up swells from storms all over the Pacific Ocean.
In this particular study, Aster and his colleagues tried to single out just the most powerful storms -- those with winds of at least 55 miles per hour.
As for what this says about global warming, it's some confirmation of the meteorological effects of climate change, but it's too short a record, in itself, to make a separate case for global warming.
"It's an interesting way of looking at it, but I'd like to see more data," commented David Salzberg, a private industry seismologist attending the meeting.
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