Researchers from the University of Tokyo have uncovered a rarely detected type of seismic wave deep inside of the Earth stemming from a "weather bomb," an extratropical storm that is small, fast-developing and possesses central pressure that rapidly increases in intensity. The findings could help scientists map out the hidden, deeper structure of the Earth.
Despite their rapidly intensifying central pressure – typically more than one millibar per hour for the course of 24 hours – weather bombs are fairly small storms. However, their fast-moving nature creates steep pressure gradients, leading to the formation of strong winds.
In the current study, the weather bomb occurred between Greenland and Iceland in 2014, creating a pressure pulse that spread to the seafloor and transformed into microseismic waves – tremors deep inside of the Earth that stem from natural phenomena – that rippled through both the surface and interior of the Earth.
Microseismic waves are detectable as both surface and body waves. Although it is typically not possible for surface waves to be observed past the coast, body waves make their way deep into the Earth's interior and can be detected by land-based seismic stations, making them ideal for deconstructing the internal structure of the Earth.
Body waves can be split into two categories: P-waves and S-waves. P-waves contain particles that move parallel to the direction of the waves' motion, whereas the particles in S-waves move perpendicular to the direction of the waves' motion. While seismologists frequently detect P-waves, the detection of S-waves by seismic stations is not a common occurrence.
Thanks to the Atlantic weather bomb, the current study is one of the first ever to detect S-waves, a feat that was accomplished through the use of 202 wave-detection stations. These stations were able to trace the movement and direction of the microseismic waves created by the weather bomb using "Hi-net arrays."
Hi-net arrays work by taking the information gathered by seismometers that pick up the "noise" created by microseismic waves as they move through the various layers of the Earth and transforming it into electronic data that can be charted and analyzed in the lab.
The successful detection of rare S-waves provides seismologists with a novel method of uncovering the Earth's deeper structure. S-waves are of particular use due to the fact that they are more sensitive to liquids than other waveforms, meaning scientists can use them to determine areas of the Earth's interior where solids turn into liquids.
"This [study] demonstrates the connection of the solid Earth to the atmosphere and ocean climate system," said Peter Bromirski, a geophysical oceanographer who co-authored a perspective on the current study. "New discoveries of any kind are always exciting, particularly when multiple fields of study are involved."
The findings were published in the journal Science.
