Fin whale song - one of the strongest animal calls in the ocean - can be used as a seismic source for probing the structure of Earth's crust at the seafloor, researchers report. While the novel method produces lower-resolution results compared to the high-energy air-gun signals commonly used in seismic ocean surveys, the abundant and globally available fin whale calls could complement and enhance seismic studies where conventional techniques cannot be used. Surveying the structure of the ocean crust often requires powerful seismic waves. This is most commonly done using ship-based air-guns, which generate explosive, high-decibel pulses. Although effective, these blasts are among the loudest human-made sounds in the ocean and are potentially harmful to ocean life. However, fin whale songs, which can be as loud as large ships and last for hours, occur at frequencies known to travel well through the ocean floor, and are often captured by the ocean-bottom seismometer (OBS) stations used to record and monitor earthquake activity. Here, Václav Kuna and John Nábelek show that not only do OBS recordings capture the whale songs but, the powerful sound waves these songs produce reverberate and refract through the layers of rock beneath the station. Kuna and Nábelek analyzed a total of six fin whale songs recorded by OBS stations off the coast of Oregon and found that they were able to use the signals to constrain the thickness and seismic velocity of the oceanic sediment and the basaltic basement, as well as the P-wave velocity of the lower crust underlying the stations. "More generally, our study demonstrates that animal vocalizations are useful not only for studying the animals themselves but also for investigating the environment that they inhabit," write the authors.
For reporters interested in trends, a February 2020 Review in Science addressed how the rapidly changing soundscape of modern oceans impacts marine life worldwide. https://science.sciencemag.org/cgi/doi/10.1126/science.aba4658