Along the coast, waves break with a familiar sound. The gentle swash of the surf on the seashore can lull us to sleep, while the pounding of storm surge warns us to seek shelter.
Yet these are but a sample of the sounds that come from the coast. Most of the acoustic energy from the surf is far too low in frequency for us to hear, traveling through the air as infrasound and through the ground as seismic waves.
Scientists at UC Santa Barbara have recently characterized these low-frequency signals to track breaking ocean waves. In a study published in Geophysical Journal International, they were able to identify the acoustic and seismic signatures of breaking waves and locate where along the coast the signals came from. The team hopes to develop this into a method for monitoring the sea conditions using acoustic and seismic data.
The low rumble of the waves
The surf produces infrasound and seismic waves in addition to the higher frequency sound we hear at the beach. Exactly how this works is still an open question, but scientists believe it’s connected to the air that mixes into a breaking wave. “All those bubbles oscillate due to the pressure instability, expanding and contracting basically in synch,” said first author Jeremy Francoeur, a former graduate student in Professor Robin Matoza’s group. This generates an acoustic signal that transfers into the air at the sea surface and into the ground on the sea floor…