Satellite view of North America's Pacific Coast.
Earth is constantly humming, some parts louder than others. The mysterious low-frequency buzz was discovered in 1998, and scientists eventually determined it was caused not by earthquakes or atmospheric turbulence, but by ocean waves colliding with the seafloor.
Now, researchers have pinpointed the source of Earth’s “background noise,” and it looks like it’s coming primarily from the Pacific coast of North America. According to Wired magazine:
When two waves of opposite direction but similar frequency collide, they create a special kind of pressure wave that carries energy to the ocean bottom. As these waves pound against the sea floor, they generate a constant vibration with a frequency of about 10 millihertz, much too low for humans to hear but easily detectable with seismometers. By comparing the intensity of the hum with the height of waves around the world, scientists can track where the buzz is coming from.Waves from the deep ocean don’t seem to make much hum at all, the researchers said.
Previous studies suggested that waves from both shallow continental shelves and the deep ocean contribute to the Earth’s hum, but new data indicates otherwise. Based on measurements from a seismic observatory called the USArray EarthScope, most of the hum appears to originate from the Pacific coast of North America, with a smaller contribution from the west coast of Europe.
Click here for the complete Wired article.