More Extreme Ocean Storms

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” … a good example of the “Cinderella science”-unloved
and overlooked-that often support significant discoveries.”
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Seismological Society of America
Public release date: 17-Apr-2008

Contact: Nan Broadbent
press@seismosoc.org
408-431-9885

Tiny tremors can track extreme storms in a warming planet

SANTA FE, New Mexico–Data from faint earth
tremors caused by wind-driven ocean waves-often
dismissed as “background noise” at seismographic
stations around the world-suggest extreme ocean
storms have become more frequent over the past
three decades, according to research presented at
the annual meeting of the Seismological Society
of America.

The International Panel on Climate Change (IPCC)
and other prominent researchers have predicted
that stronger and more frequent storms may occur
as a result of global warming trends. The tiny
tremors, or microseisms, offer a new way to
discover whether these predictions are already
coming true, said Richard Aster, a geophysics
professor at the New Mexico Institute of Mining
and Technology.

Unceasing as the ocean waves that trigger them,
the microseisms show up as five- to 30-second
oscillations of Earth’s surface at seismographic
stations around the world. Even seismic
monitoring stations “in the middle of a continent
are sensitive to the waves crashing all around
the continent,” Aster said.

As storm winds drive ocean waves higher, the
microseism signals increase their amplitude as
well, offering a unique way to track storm
intensities across seasons, over time, and at
different geographical locations. For instance,
Aster and colleagues Daniel McNamara from the
U.S. Geological Survey and Peter Bromirski of the
Scripps Institution of Oceanography recently
published analysis in the Seismological Society
of America journal Seismological Research Letters
showing that microseism data collected around the
Pacific Basin and throughout the world could be
used to detect and quantify wave activity from
multi-year events such as the El Niño and La Niña
ocean disruptions.

The findings spurred them to look for a
microseism signal that would reveal whether
extreme storms were becoming more common in a
warming world. In fact, they saw “a remarkable
thing,” among the worldwide microseism data
collected from 1972 to 2008, Aster recalled. In
22 of the 22 stations included in the study, the
number of extreme storm events had increased over
time, they found.

While the work on evaluating changes in extreme
storms is “still very much in its early stages”,
Aster is “hoping that the study will offer a much
more global look” at the effects of climate
change on extreme storms and the wind-driven
waves that they produce. At the moment, most of
the evidence linking the two comes from studies
of hurricane intensity and shoreline erosion in
specific regions such as the Pacific Northwest
Gulf of Mexico, he noted.

The researchers are also working on recovering
and digitizing older microseism records,
potentially creating a data set that stretches
back to the 1930s. Aster praised the work of the
long-term observatories that have collected the
records, calling them a good example of the
“Cinderella science”-unloved and overlooked-that
often support significant discoveries.

“It’s absolutely great data on the state of the
planet. We took a prosaic time series, and found
something very interesting in it,” he said.

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Presentation: “Microseism-Based Climate
Monitoring” in the session: Models, Methods, and
Measurements: Seismic Monitoring Research. 8:30 –
Noon (Mountain), April 17, 2008.

Aster, R. New Mexico Institute of Mining and
Technology; McNamara, D., U.S. Geological Survey
in Golden, CO; Bromirski, P., Scripps Institution
of Oceanography; and Gee, L., and Hutt, C.R.,
U.S. Geological Survey in Albuquerque, NM.

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