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Whale Calls Reverberate Through Earth's Crust

Study finds that Fin whale songs are powerful enough to reverberate through the Earth’s crust, allowing scientists to study its thickness and structure.

Whale songs suffuse the ocean depths with waves of sound that can travel thousands of miles. Now, scientists have figured out they can use the whales’ underwater serenades to study the seafloor, reports Smithsonian Magazine.

To study the Earth’s crust beneath the oceans, scientists use the way vibrations travel through the layers of sediment and rock to decipher details about their composition and structure. But crust-rattling vibrations like that don't come around every day. Traditionally, researchers have had to wait for jolts of tectonic activity to generate seismic vibrations, but undersea earthquakes aren’t always reliable collaborators.

The new study, published last week in the journal Science, detected the calls of fin whales, one of the loudest creatures in the sea, via 54 ocean-bottom seismometers that were poised to detect undersea quakes. Unexpectedly, the researchers found that the fin whales’ vocalizations were powerful enough to reverberate through the Earth’s crust.

“The calls travel through the water and penetrate into the ground,” says Václav Kuna, a seismologist and co-author of the research. “They then bounce off the layers within the oceanic crust and come back to the surface where we record them.”

Between 2012 and 2013, four of the seismometers stationed in the northeast Pacific Ocean recorded six fin whale songs ranging from 2.5 to almost 5 hours in length. The whale chatter translated to seismic waves powerful enough to allow Kuna and his colleagues to peer 8,200 feet below the ocean bottom. Fin whale calls can reach 189 decibels, which is nearly equal to the maritime din of a container ship.

These recordings suggest whale songs could be used as a way to estimate the varying thickness and geology of the Earth’s crust without waiting for tectonic activity.

In the region the whale songs were picked up, the calls revealed an upper sedimentary layer ranging from around 1,300 to 2,100 feet thick sitting on top of a rocky layer of basalt more than a mile thick that was in turn undergirded by a type of oceanic rock called gabbro.

Kuna says he’s hoping other researchers can apply the technique for other types of studies. “This study was a proof of a concept,” he tells Science. “I’m putting it out there for other people to find more uses for this.”


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