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World's largest subwoofer: Earthquakes 'pump' ground to produce infrasound

19.10.2012
Earthquakes sway buildings, buckle terrain, and rumble – both audibly and in infrasound, frequencies below the threshold of human hearing. New computer modeling by a team of researchers indicates that most of the low-frequency infrasound comes from an unexpected source: the actual "pumping" of the Earth's surface. The researchers confirmed their models by studying data from an actual earthquake.

"It's basically like a loudspeaker," said Stephen Arrowsmith, a researcher with the Geophysics Group at Los Alamos National Laboratory in Santa Fe, N.M., who presents his team's findings at the 164th meeting of the Acoustical Society of America (ASA), held Oct. 22 – 26 in Kansas City, Missouri. "In much the same way that a subwoofer vibrates air to create deep and thunderous base notes, earthquakes pump and vibrate the atmosphere producing sounds below the threshold of human hearing."

Infrasound can reveal important details about an earthquake. In particular, it may be used to measure the amount of ground shaking in the immediate region above the source, which would normally require an array of many seismometers to measure. There is therefore potential to use infrasound to assess damage in the immediate aftermath of an earthquake.

To better understand the relationship between earthquakes and infrasound, the researchers used the basic idea that the Earth's surface above the earthquake pumps the atmosphere like a piston. They were then able to apply the same modeling approach used on loudspeaker dynamics.

The researchers tested their model by comparing its predictions to actual data collected from a magnitude 4.6-earthquake that occurred on January 3, 2011, in Circleville, Utah. The University of Utah maintains seismograph stations across the state supplemented with infrasound sensors, which recorded the infrasound produced during that event. Their predictions were in good agreement with the actual data, suggesting that earthquakes generate most of their sound by pumping the atmosphere like a loudspeaker.

"This was very exciting because it is the first such clear agreement in infrasound predictions from an earthquake," said Arrowsmith. "Predicting infrasound is complex because winds can distort the signal and our results also suggest we are getting better at correcting for wind effects."

Until now, seismologists have not understood the relative importance of the simple pumping of the ground versus other mechanisms for generating infrasound.

Additional members of the research team include Relu Burlacu and Kristine Pankow, University of Utah; Brian Stump and Chris Haward, Southern Methodist University; and Richard Stead and Rod Whitaker, Los Alamos National Laboratory.

MORE INFORMATION ABOUT THE 164th ASA MEETING

The Kansas City Marriott Downtown Hotel is located at 200 West 12th Street, Kansas City, Missouri, 64105. The hotel main numbers are: 816-421-6800; fax: 816-855-4418.

USEFUL LINKS

Main meeting website: http://acousticalsociety.org/meetings/kansas_city
Meeting Abstract Database: http://asa.aip.org/asasearch.html
Hotel site: https://resweb.passkey.com/Resweb.do?mode=welcome_ei_new&eventID=8120158
WORLD WIDE PRESS ROOM

ASA's World Wide Press Room contains additional tips about newsworthy stories and with lay-language papers, which are 300-1200 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio, and video.
PRESS REGISTRATION

ASA will grant free registration to credentialed full-time journalists and professional freelance journalists working on assignment for major news outlets. If you are a reporter and would like to attend, contact Charles E. Blue (cblue@aip.org, 301-209-3091), who can also help with setting up interviews and obtaining images, sound clips, or background information.

This news release was prepared for the Acoustical Society of America (ASA) by the American Institute of Physics (AIP).
ABOUT THE ACOUSTICAL SOCIETY OF AMERICA

The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world's leading journal on acoustics), Acoustics Today magazine, ECHOES newsletter, books, and standards on acoustics. The Society also holds two major scientific meetings each year.

Charles E. Blue | EurekAlert!
Further information:
http://www.aip.org
http://www.acousticalsociety.org

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