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PODCAST: Listening to the Earth

On this week's podcast I talked to people who listen to the Earth. Scientists monitor seismic waves that bounce through the planet's crust, sound waves too low for the human ear to hear reverberating through the atmosphere and hydroacoustic waves moving through the oceans. These signals carry with them lots of information about the sources of the disturbances, like where they happened and whether they're from an earthquake, a volcano or a large explosion.

The Comprehensive Nuclear Test Ban Treaty Organization's International Monitoring System listens for these kinds of signals. It's primary job it to detect secret nuclear tests, but it can do so much more. When it's finished it'll have more than 250 monitoring stations that can listen to all kinds of seismic and acoustic waves.

Seismic monitoring stations make up by far the largest proportion of the International Monitoring System. Right now there are 42 primary and 102 secondary seismic stations across the globe.

Seismic stations are buried underground, making them difficult to photograph. There's a primary station under Torodi, Niger ...

... an auxiliary station in Charters Towers, Australia...

... and auxiliary station in Bilibion Russia, one of the most remote parts of the country.

Sixty planned infrasound stations around the world listen for ultra-low frequency sound waves emitted
by giant blasts.

Already 45 have been installed the world over. This one is installed in Qaanaaq, Norway....

...Tristan da Cunha in the United Kingdom...

...and at Windless Bight Antartica (it gets buried by snow a lot).

Underwater microphones listen for hydroacoustic waves moving through the oceans.

Right now there are ten such stations. Sound waves travel far easier under water than in the air, meaning only about a dozen are needed to effectively cover all the world's oceans. Underwater listening devices getting ready for deployment off the coast of the British Indian Ocean Territory...
... a diver inspects the underwater cable that carries signals from the hydrophones to their nearby shore facility...

...the shore facility with its transmission antenna at the British Indian Ocean Territory.

All images copyright CTBTO Preparatory Commission


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