Fin whale (acceleration 6x and 12x)

Below: two stereo spectrograms of fin whale vocalisations, recorded in the North Atlantic Ocean, southwest of Ireland. While these vocalisations are commonly called ’20 Hz pulses’, their frequency ranges from about 30 Hz down to 15 Hz, in a downward swoop. These fin whale calls are below the human hearing range, but they are among the loudest biophonic sounds in the ocean and reach underwater sound pressure levels of up to 186 dB. This makes them very useful to study the whales’ migration patterns (Dréo, R. et al 2018) and even to perform seismic studies of the crust where conventional air-gun surveys are not available (Kuna et al.2021)

These stereo tracks, presented at two different modes of acceleration, are renderings of the 3 components of the motion of the seafloor at a 3.9 km depth, southwest of Ireland. The seismograms were recorded on 07 April, 2020, between 13.50 and 14.30 GMT by the ocean-bottom seismic station BRIAN of the SEA-SEIS network. Bandpass filtering and noise reduction was applied to this recording to enhance the audio quality.

At this level of acceleration (6x), one can experience the intensity and low frequency quality of the calls as well as their reflections (echoes) from the seabed and the ocean surface. Over the course of the recording one can also hear the whale moving across the stereo image.

At this level of acceleration (12x), one can experience the whale moving across the stereo image. Enhancing the audio quality through careful processing further reveals that there may be more than one whale recorded by the seismometer.