If you play back this audio file, you’ll be listening to a couple of fin whales and an earthquake, and according to my dog, that’s some exciting stuff. No, seriously, I played it on my laptop the other day, and Trooper got all agitated, and started growling and barking in what I can only assume was confusion. (“where’s the fin whale?? it’s got to be around here somewhere!”)
The colorful figure at the top of the post is called a spectrogram. Time marches across to the right. Frequency increases upward. And the colors basically indicate loudness – brighter colors are louder. This particular chunk of data was recorded in the dead of winter just off the coast of British Columbia, Canada, under more than a kilometer of water. Even though the instrument is designed to measure earthquakes, it also picks up the very low, booming calls of fin and blue whales. The spectrogram shows two slightly different calls alternating – one slightly higher pitched and one slightly lower. We believe this is probably two fin whales passing near the seismometer.
You might notice that the audio clip is about 30 seconds long, but the spectrogram shows five minutes of data – that’s because the calls are down around 20 Hz, which is at the very lower end of the human hearing range. (If you have tip top hearing, you are probably sensitive to sounds between 20 Hz and 20 kHz.) I sped up the audio by a factor of 10, so that we can actually hear it – bloop… bloop… bloop…
At about 10:03am in the spectrogram, and 20 seconds into the audio recording, you can see/hear an earthquake in the background. My seismologist colleagues tell me that this isn’t the distinctive crack of a primary or secondary phase arrival from an earthquake, but possibly the rumbling caused by a tertiary, or “T phase”, arrival.
So why did Trooper have a meltdown? I guess you would too, if you thought you were suddenly surrounded by a couple of super high-pitched fin whales and an earthquake.