Scientists have known for a while that Earth "rings" due to seismic activity, but now they are narrowing in on the dominant cause of our planet's continuous background "hum."
Seismic waves created by earthquakes and volcanic activity create primary and secondary waves (taught in most geology classes as p-waves and s-waves, respectively). Both types are body waves, meaning they travel through the Earth's interior, not along its surface. Following a major seismic event, scientists map where and when these waves are detected around the globe to probe the interior structure of our planet. This is how we determined the existence of our solid inner core and liquid outer core.
The propagation of seismic waves can cause Earth to ring like a bell on the order of days, weeks, or months depending on the triggering event. And scientists have a decent understanding of the frequencies of these oscillations. However, over the past several decades, scientists have detected even lower frequency vibrations. These new signals are constant and don't appear to correlate with any seismic activity.
Many theories have been thrown around to explain this background hum, but there was no way test these theories until now. Researchers in France have recently created detailed models of ocean waves which show that long, slow, deep ocean waves can generate "microseismic" activity along the ocean floor significant enough to induce planet-wide vibrations. This video from MIT (not directly related to this story) shows how large-amplitude underwater waves can form and then have strong impacts on the sea floor as well as the continental shelf.
Fabrice Ardhuin is a senior research scientist at Centre National de la Recherche Scientifique in Brest, France, and lead author of the new research. Ardhuin said understanding where these seismic signals are coming from also enables researchers to look for even fainter seismic signals. That could allow scientists to better detect faint earthquakes far away from seismic stations or nuclear explosions, he said.
"I think it is a relief to the seismologists," Ardhuin said of figuring out the source of Earth's ringing. "Now we know where this ringing comes from, and the next question is what can we do with it."
Here's some geek you can do whatever you like with:
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Keep on geeking!
@Summer_Ash, In-house Astrophysicist