With a call as loud as a large ship, fin whales (Balaenoptera physalus) are among the noisiest creatures in the sea. For some seismologists who monitor earthquakes by recording seafloor vibrations, cetacean calls are a nuisance because the racket muffles their measurements. But for two earthquake researchers, they found whale vocalization reflections could assist in measuring ocean crust structure. Their findings appear today (February 12) in Science.
“It’s a nice example of how we make use of the data the planet provides for us,” Jackie Caplan-Auerbach, a seismologist and volcanologist at Western Washington University who was not involved with the work, tells The New York Times.
Ocean-bottom seismology stations are designed to monitor earthquakes, and often pick up whale songs. Researchers have previously used these incidental recordings to track fin whale movements, but this is the first time whale calls have been used to study the planet.
See “Cetacean Cacophony”
Seismologists Václav Kuna of the Institute of Geophysics of the Czech Academy of Sciences in Prague and John Nábelek of Oregon State University analyzed six fin whale songs that were recorded by seismometers deployed in the Pacific Ocean off the coast of Oregon. When whale calls hit the seafloor, some of these sound waves are converted into seismic waves that travel through the layers of the ocean crust. The waves eventually bounce back to the surface layer where they’re picked up by a seismometer. By measuring the time it took for the waves to reflect back, they could estimate the thickness of each crust layer.
To study ocean sediment structure, scientists have previously relied on airguns, which generate soundwaves by blasting pressurized air at the seafloor. Noise pollution from these devices can be harmful to marine life. Kuna tells Science that whale call analysis could provide a more environmentally friendly approach to studying the ocean crust, especially in marine reserves where airguns are banned. This method is unlikely to fully replace airgun surveys because fin whale calls don’t penetrate as deeply into the ocean crust, providing a less detailed picture of the ocean substrate, Science reports.