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Thursday, March 8, 2012

Audio: That's Not Thunder? The Seismic Waves of Japan's 9.0 Earthquake

The seismic waves of an earthquake are too low or "bassy" for the human ear.  This range, below 20Hz, is called "infrasound."  These frequencies can be shifted upward in range via pitch shift or sample rate changes.

This is what Georgia Tech scientists have done with the data gathered from last year's Tohoku-Oki, Japan earthquake.

The most compelling clip, "Movie S3", sounds almost indistinguishable from thunder.  This uncanny faulty recognition can cause a rather visceral reaction.  It is what I will remember most about this Georgia Tech paper.

"Movie S3  Example of the mainshock and early aftershock recordings during the 2011 Mw 9.0 Tohoku-Oki earthquake. (Top) Vertical-component velocity seismogram recorded at Hi-net station HATH. (Middle) 20 Hz high-pass-filtered envelope functions highlighting the mainshock and early aftershock signals. The envelope function is smoothed with a half width of 50 data points and is in base 10 logarithmic scale. The black lines marked the predicted P-wave arrivals of aftershocks around the mainshock slip region as listed in the Japan Meteorological Agency (JMA) earthquake catalog.  (Bottom) The spectrogram. The sound is generated by speeding up the seismic data by 100 times."

Read the paper HERE
Find all the movies HERE
Read Georgia Tech's release HERE
Read the Boing Boing Article HERE  
Listen to a Neil deGrasse Tyson interview and read more about Infrasound in my post on Ghost Sightings and Infrasound HERE

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