Seismic waves indicate a fifth layer in the Earth’s core

21 Feb. () –

Data obtained from seismic waves caused by earthquakes have shed new light on the deepest parts of the inner core of the Earth.

By measuring the different speeds at which these waves penetrate and pass through the Earth’s inner core, researchers at the ANU (Australian National University) believe they have documented evidence for the existence of a distinct layer within the Earth known as the outermost core. deep: a solid “metal ball” that sits in the center of the inner core.

Until recently it was thought that the Earth’s structure was made up of four distinct layers: the crust, the mantle, the outer core, and the inner core. The findings, published in Nature Communicationsconfirm the existence of a fifth layer.

“The existence of an internal metallic ball within the inner core, the innermost core, was hypothesized about 20 years ago. We now provide another line of evidence to prove the hypothesis.said Dr. Thanh-Son Ph?m, of the ANU Research School of Earth Sciences.

Professor Hrvoje Tkalcic, also from ANU, said that studying the deep interior of Earth’s inner core can tell us more about our planet’s past and evolution.

“This inner core is like a time capsule of Earth’s evolutionary history: it’s a fossilized record that serves as a gateway to events in our planet’s past. Events that occurred on Earth hundreds of millions or billions of years ago.” explained.

The researchers analyzed seismic waves that travel directly through the center of the Earth and “spit” them out on the opposite side of the globe from the location where the quake struck, also known as the antipode. The waves then return to the origin of the earthquake.

The ANU scientists describe this process as similar to the bouncing of a ping pong ball.

“By developing a technique to augment the signals recorded by densely populated seismograph networks, we have observed, for the first time, seismic waves that bounce back and forth up to five times along the diameter of the Earth. Previous studies had only documented a single antipodal rebound,” says Dr. Pham.

“The findings are exciting because they provide a new way to probe Earth’s inner core and its most central region.”

One of the earthquakes studied by scientists originated in Alaska. Seismic waves from this quake “bounced” somewhere in the South Atlantic, before traveling back to Alaska.

The researchers studied the anisotropy of the iron-nickel alloy that makes up the interior of Earth’s inner core. Anisotropy is used to describe how seismic waves they speed up or slow down through Earth’s inner core material depending on the direction in which they travel. It could be due to the different arrangement of the iron atoms at high temperatures and pressures or the preferential alignment of the growing crystals.

They found that the rebounding of seismic waves repeatedly probed points near the center of the Earth from different angles. By analyzing the variation in travel times of seismic waves in different earthquakes, scientists deduce that the crystallized structure of the innermost region of the inner core is probably different from that of the outer shell.

They claim this could explain why the waves speed up or slow down depending on their angle of entry as they penetrate the innermost core.

According to the ANU team, the findings suggest that at some point in Earth’s evolution there may have been a major global event that caused “significant” change. in the crystalline structure or texture of the Earth’s inner core.

“There are still many unanswered questions about Earth’s innermost core, which could hold the secrets to unlocking the mystery of our planet’s formation,” said Professor Tkalcic.

the researchers They analyzed data from about 200 earthquakes of magnitude 6 or greater in the past decade.