In the days and weeks following the 9.0-magnitude earthquake and ensuing tsunami in Japan, the world was bombarded with disturbing images and video of overturned cars and boats, splintered homes and even leveled neighborhoods. But hearing the earthquake -- from its initial blast to the series of the plate-slipping pops that follow -- might provide a clearer picture of its power.
Thousands of seismometers are located in the region, making the March 11 event the best-recorded earthquake of all-time. Zhigang Peng, an associate professor at Georgia Tech's School of Earth and Atmospheric Sciences, helped bring that data to life.
Peng converted the seismic waves into audio files so everyday folk could "hear" what the quake sounded like as it moved through the earth and around the globe. Peng's research, which was supported in part by the National Science Foundation, was published in the March/April edition of Seismological Research Letters. Peng has made audio files of quakes in the past. But he saw the Tohoku-Oki earthquake as an opportunity to educate general audiences.
The measurement, which is in the animation above, was taken near the coastline of Japan between Fukushima and Tokyo. The initial roar that you hear is the 9.0 mainshock. The popping noises that immediately follow is the sound of the earth's plates slipping dozens of meters into new positions, which triggered aftershocks. Some of these plates moved as much as 50 meters, Peng said. He has since updated the animation and slowed it down a bit to allow audiences to hear more clearly.
To be clear, the sound is not what folks at the epicenter of the quake heard, Peng explained to me today. In real time, the earthquake and aftershocks went on for hours. The clip above is only 37 seconds. Peng, and other collaborators in the United States and Japan, took the data and played it faster than true speed to increase the frequency to audible levels. The process also allows audiences to hear data recorded over minutes or hours in a matter of seconds.
The next clip is taken from measurements in California. While considerably quieter, that initial noise corresponds with the Japanese mainshock. The high-pitch continuous sound that follows -- described as rainfall that turns on and off -- represents induced tremor activity at the San Andreas Fault. Peng said the audio file was particularly interesting because it illustrated how earthquakes interact.
Photo: Takashi NAKANO via Flickr user Tex Texin, CC 2.0
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