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Japanese Earthquake: Seismic Waves Converted To Audio (LISTEN)

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Devastation shown from a tsunami following the Japan earthquake
Devastation shown from a tsunami following the Japan earthquake

Last year’s 9.0 magnitude earthquake in Japan was the fourth largest since 1900.

The Tohoku-Oki struck on March 11, triggering a tsunami which killed around 19,000 people along the country’s north eastern coast.

Now Zhigang Peng, associate professor in Georgia Tech's School of Earth and Atmospheric Sciences, has converted the earthquake's seismic waves into audio files.

The results allow experts and general audiences to "hear" what the quake sounded like as it moved through the earth and around the globe.

"We're able to bring earthquake data to life by combining seismic auditory and visual information," said Peng, whose research appears in the March/April edition of Seismological Research Letters.

"People are able to hear pitch and amplitude changes while watching seismic frequency changes. Audiences can relate the earthquake signals to familiar sounds such as thunder, popcorn popping and fireworks."

The different sounds can help explain various aspects of the earthquake sequence, including the mainshock and nearby aftershocks.

For example, this measurement was taken near the coastline of Japan between Fukushima (the nuclear reactor site) and Tokyo. The initial blast of sound is the 9.0 mainshock. As the earth's plates slipped dozens of meters into new positions, aftershocks occured.

They are indicated by "pop" noises immediately following the mainshock sound. These plate adjustments will likely continue for years.

As the waves from the earthquake moved through the earth, they also triggered new earthquakes thousands of miles away.

In this example, taken from measurements in California, the quake created subtle movements deep in the San Andreas Fault.

The initial noise, which sounds like distant thunder, corresponds with the Japanese mainshock. Afterwards, a continuous high-pitch sound, similar to rainfall that turns on and off, represents induced tremor activity at the fault. The animations not only help scientists explain the concept of distant triggering to general audiences, but also provides a useful tool for researchers to better identify and understand such seismic signals in other regions.

This third recording was taken about 90 miles from the Japanese earthquake's epicenter. There are two distinct sound waves, both are caused by the mainshock.

A "pop" is heard 90 seconds (in actual time) after the main event. This pop wasn't recorded at any other nearby stations, leading Peng to believe that either the ground shifted immediately under the measuring station, or the hill slope where the station sits helped to amplify the shaking. It was the strongest reading he found - a ground acceleration of nearly three g.

The human ear is able to hear sounds for frequencies between 20 Hz and 20 kHz, a range on the high end for earthquake signals recorded by seismometers.

Peng, graduate student Chastity Aiken and other collaborators in the U.S. and Japan simply played the data 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.

As Japan approaches its first anniversary since the devastating tsunami, the country’s clean-up effort has been making striking progress.

In this set of before and after pictures, scenes of the devastation are juxtaposed with images of the same spots, cleaned of debris and effectively reclaimed by the Japanese people.

A surge of water from the tsunami caused by the quake knocked out power at the coastal Fukushima plant, leading to the worst nuclear disaster since Chernobyl.

Tens of thousands have had to leave the area, and it's unclear whether some will ever be able to move back.

Volunteer and governmental organisations have worked tirelessly to restore the country, and as these pictures reveal, the results show for themselves.

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