For the first time ever, a team of scientists in Japan has detected a rare kind of earthquake on the ocean floor.
Microseisms are faint earthquake tremors caused by “the sloshing of the ocean’s waves on the solid Earth floor during storms,” the American Association for the Advancement of Science explains in a press release. And there are two kinds of microseisms: P-wave microseisms (the faint tremors that animals can detect before an earthquake), which have been charted before, and S-wave microseisms (the strong tremors that humans detect during an earthquake).
Scientists study P- and S-waves because they unlock information about the Earth’s interior. When P- and S-waves travel through the Earth after an earthquake they can be stopped, reflected, or redirected based on the different chemical and physical structures they encounter. By tracking the route and actions of these waves, scientists can identify more details about the Earth’s mantle and crust.
But until now, S-wave microseisms have remained elusive.
In a paper published Friday in the journal Science, earthquake researchers Kiwamu Nishida, with the Earthquake Research Institute at the University of Tokyo, and Ryota Takagi, with the Research Center for Prediction of Earthquakes and Volcanic Eruptions at Tohoku University, have detected both P- and S-wave microseisms.
The two researchers attribute their discovery to a “weather bomb” that occurred in the North Atlantic ocean near Greenland in 2014.
“This is where severe oceanic storms can help,” New Scientist explains. “Atmospheric pressure can drop rapidly during these events, generating oceanic waves so strong that a small fraction of their energy makes it all the way down to the sea floor and generates faint P-waves and S-waves in the rocks – as if a very weak earthquake has occurred.”
Professor Nishida and Professor Takagi were able to capture a high-resolution image of the Earth’s internal structure below the weather bomb by recording the P- and S-waves.
“Seismic tomography is like an x-ray of Earth’s interior, except that it uses earthquakes for the illumination,” Nishida and Takagi write in their paper. “Earthquakes are imperfect illuminators because they are clustered on plate boundaries, leaving much of the interior in the shadows.”
And unlike earthquakes, weather bombs can occur almost anywhere in the ocean.
“We’re potentially getting a suite of new seismic source locations that can be used to investigate the interior of the Earth,” Peter Bromirski, a geophysical oceanographer at the Scripps Institution of Oceanography in California, told Wired.
Researchers believe this discovery will allow for better understanding of the Earth’s interior, as well as better detection of earthquakes and oceanic storms.