In a paper published Friday in the journal Science,  two Japanese earthquake researchers were able to identify two kinds of elusive microseisms for the first time on the ocean floor that they attribute to a severe North Atlantic storm near Greenland or “weather bomb” which occurred in 2014. With the discovery the researchers hope it will tell them more about the Earth’s crust by essentially being given an x-ray of the interior of our planet.

Weather Bomb
Image source: Wikimedia Commons

Weather bomb in 2014 affected travel in UK

The same storm that allowed for the identification of the microseisms, which was published today, cut power to over 20,000 homes in Northern Ireland, Wales, Northern England and Scotland while also essentially shutting down ferry service. While that many not have been pleasant for those that were affected, 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, were afforded the opportunity to  detect both P- and S-wave microseisms.

Microseisms are the faintest of tremors, which according to the American Association for the Advancement of Science are caused by “the sloshing of the ocean’s waves on the solid Earth floor during storms.” If you live in an earthquake prone region as I do in Guatemala, there are occasions when you’re privy to your cats bolting inside as dogs around the neighborhood all bark at the same time. These are P-wave microseisms, which on a rare occasion if you’ve lived through enough can get you under a door frame before the real shaking begins. These P-wave microseisms are not detectable by humans or even their instrumentation until now.

S-wave microseisms, are perceptible to humans and often grow to the large tremors that start throwing your possessions to the floor and have you saying, “oh sh*t.”

By tracking these waves, researchers are gifted a look inside the Earth’s mantle and crust as they are often redirected, reflected or stopped as they pass through the Earth.

Essentially the waves from the “weather bomb” were big enough that there was enough energy left that the wave from the surface became a wave striking the ocean floor creating these microseisms, that resemble very weak earthquakes.

“Seismic tomography is like an x-ray of Earth’s interior, except that it uses earthquakes for the illumination,” Nishida and Takagi wrote in their paper. “Earthquakes are imperfect illuminators because they are clustered on plate boundaries, leaving much of the interior in the shadows.”

More information on the usefulness of this paper

Peter Bromirski, a geophysical oceanographer at the Scripps Institution of Oceanography at the University of California in San Diego explained the usefulness of this study commentary  that accompanied the paper published today also in Science. While not involved in the study by Nishida and Takagi he further explains the study of microseisms.

“Most of what we know about the internal structure of the Earth has been determined from studying the way earthquake waves propagate, through the lower crust and the mantle and the core,” Dr Bromirski told the BBC.

“In order to do that, you need to have a source that can generate a signal that propagates to your seismic stations. For some reason there are very few earthquakes in the mid Pacific… so we don’t have any sources there.

“These storm-generated P and S wave microseisms will hopefully allow us to better characterise the structure of the Earth below the Pacific.