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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. 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. Related Links: |
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