for National Geographic News
Extreme ocean storms have ramped up in frequency over the past 30 years, according to new research based on small tremors.
The faint tremors, called microseisms, are periodic movements of Earth's surface that can last anywhere from 5 to 30 seconds.
Unlike earthquakes, which are caused by movements of Earth's tectonic plates, microseisms are created by the incessant beating of waves along the coasts.
The phenomena are usually dismissed as background noise by scientists studying earthquake readings.
"The gist is that we monitor pervasive seismic tremors observed around the world that arise from wind-generated waves to [assess] Earth's wave climate," said study co-author Richard Aster, a geophysics professor at the New Mexico Institute of Mining and Technology.
The new findings, while still in their early stages, could be used to test long-held theories about whether global warming leads to more violent ocean storms, Aster added.
(Related news: "Hurricanes Have Doubled Due to Global Warming, Study Says" [July 30, 2007].)
Aster and colleagues studied microseisms at 22 seismographic stations scattered across the world, from Antarctica to Pittsburgh, Pennsylvania.
They also looked at worldwide ocean-borne microseism data taken from 1972 to 2008.
The researchers found that the microseisms' power increased with time, perhaps as storm winds intensified or changed direction.
The data also showed that each of the 22 seismographic stations registered an uptick in extreme ocean gales.
SOURCES AND RELATED WEB SITES