Fin Whale (Balaenoptera Physalus), or Finback Whale, an endangered species, is the second-largest species of fish on earth, right after the Blue Whale. Like other wales, the male fin whale makes a long, loud, low-frequency sound to attract the female whales for mating. And scientists now think that these whale songs can be used for mapping the earth.
When biologists first recorded fin whales’ sounds, they did not realise that those sounds were coming from these beautiful creatures. They thought it was an equipment malfunction or a geophysical phenomenon, but they never guessed (well, at first) that it was a whale communicating with other whales, present deep inside the ocean.
Low-Frequency, High Impact Finback Whale Songs
The sound made by finback whales is the lowest-frequency sound produced by any animal. The sounds, also called whale songs, of fin whales, can be as loud as a large ship’s horn and range up to 189 decibels. It is potent enough to penetrate the earth’s crust!
A fin whale song can penetrate as deep as 2,500 m below the seafloor, and this can potentially help geologists and seismologists gain some idea about the inner workings of the planet earth.
Of course, with such crucial information available to scientists, it became imperative for them to analyse it and try to find something useful from it!
Vaclav Kuna from the Czech Academy of Sciences in Prague and John Nabelek of Oregon State University in Corvallis recorded and analysed six songs by a single whale. These songs were recorded in 2012 and 2013 with the help of a network of 54 ocean-bottom seismometers in the northern Pacific Ocean and lasted from 2.5 to 4.9 hours.
Each sound lasted one to two seconds, and it combined various vibrations in a patterned sequence that lasted from 7 to 15 minutes.
They noted that after each call from the whale, the other whale would answer back.
Travelling of Sound and Communication Waves
When whales make these sounds, the sound travels through the water and meets the ground, converting some of the sound waves into seismic waves.
As the sound passes through different types of rocks and bends through other materials, researchers can pick up clues as to where the sound wave has travelled.
How Can Whale Songs Help Scientists Map the Earth?
Seismic waves travel at different speeds in different materials. Reflection causes the primary (P) waves and secondary (S) waves to rebound, whereas refraction makes the waves move in different directions.
By observing the changes in the wave velocity, researchers can determine the earth’s density as a whole. In measuring the differences in these waves’ direction, the many deep layers under the earth’s crust can be identified.
Scientists study the earth’s internal structure by measuring how long it takes for a wave to reach from one point to another. These waves travel through the oceans crust and into the gabbroic lower crust, which is just under the oceans crust.
The Structure of the Earth Can Not Be Studied Directly
That is why geologists use these seismic waves to determine the depths of layers with the planet. The researchers used the whale’s recorded songs to pinpoint where the whale was at the time, and the vibrations caused due to the music helped create images of the earth’s crust layers.
Due to this study, researchers could map out the thickness of the earth’s crust in earthquake-prone zones like the Blanco Fracture Zone, which is around 100 miles west of Oregon’s Cape Blanco.
Before this finding, seismologists and oil companies used air-guns to explore underwater geology. This technology, however, was an environmental disaster. The noise from the guns harms marine life.
Fin whales sing less and flee from a site where there is seismic blasting. U.S. environmental activists have tried to stop this blasting which is very harmful to marine life.
Use of Air Guns in Oceans is Still Debatable
Jackie Caplan-Auerbach, a seismologist at Western Washington University, said, “The use of air guns is a potent tool for us because that sound can penetrate the subsurface, and the echoes tell us about what’s underground.”
She said that the ability to take what most of them considered mere background noise and make some geophysics out of it was a lovely thing to do.
Nabelek says that to make use of whale song as a source of studying earth’s crust, the sperm whales could be used as they have a slightly higher frequency than the finback whales.
Although using the naturally available whale songs was straightforward and didn’t need much capital, it is also not very precise. The air-gun is much louder and provides better sound quality for studying the crust.