Listening in on fin whale calls to do seismic sensing of the ocean floor

The song of a male fin whale calling to females is one of the most powerful vocalizations in all the oceans. The call of the up to 24 metre long giants can reach well over 180 decibels and can be heard for hundreds of kilometres underwater.  

Now Vaclav Kuna, from the Institute of Geophysics of the Czech Academy of Sciences, and Oregon State University, has shown that the fin whale song could be used as an all natural, unobtrusive way of imaging the ocean crust.

Ship based air-guns are harmful

For decades seismologists have probed the geology below the ocean floor using very loud sound pulses created by ship based air-guns. But these loud underwater thunder claps have become increasingly controversial because of concerns that they are harmful to marine life. 

From 2012 to 2013 a series of 54 ocean bottom seismometers (OBS) were deployed in the northwest Pacific ocean to monitor seismic activity where the Juan de Fuca and Pacific tectonic plates meet. These OBS recorders use sound waves to detect seismic activity, as well as thickness of sediment and rock layers immediately beneath where the devices are located.

Fin whale calls could help measure seismic activity 

OBS recorders also pick up the sound of passing ships, and, as Kuna's study revealed, the call of the fin whale. 

But the recordings also contained echoes of the fin whale calls reflected and refracted from crustal surfaces beneath the three stations studied. These reflections, Kuna believes, can be used to reconstruct features of sub-sea geology in the same way that standard seismic signals have been used. 

Kuna does not think fin whale vocalizations have the potential to replace high-energy air-gun signals in ocean crust studies. But they could be a less-intrusive complement to seismic experiments.