MercoPress. South Atlantic News Agency

Antarctica tremors help prove Earth's two speed rotation

Tremors occurred in the South Sandwich Islands near Antarctica and detected by seismometers near Fairbanks, Alaska helped elucidate a decades' long geophysics controversy regarding the Earth's rotation and magnetic field.

On their pole-to-pole journey the seismic waves traveled through the Earth and some through the inner core which helped geographic scientists find out that the Earth's moon-size inner core rotates faster than its surface by about 0.3 to 0.5 degree per year. A finding expected to end a nine-year debate.

The claim that Earth's inner core was getting ahead of itself seemed odd at first. But some computer simulations showed the molten-iron outer core dragging the inner core around by the magnetic field generated in the outer core.

Still, seismologists had problems with measurements of the inner core's excess spin.

Now the researchers found persuasive evidence that the inner core really is spinning faster than the rest of the planet, according to Xinhua.

"Extraordinary claims require extraordinary proof", said Xiaodong Song, a professor of geology at the University of Illinois at Urbana-Champaign and co-author with Paul Richards from Columbia University, of a paper published August 26 in the journal "Science". "We believe we have that proof."

Earth's iron core consists of a solid inner core about 2,400 km in diameter and a fluid outer core about 7,000 km in diameter. The inner core plays an important role in the geodynamics that generates Earth's magnetic field, and an electromagnetic torque from the geodynamics is thought to drive the inner core to rotate relative to the mantle and crust.

The original finding was based on analysis of three decades of seismological records. Scientists have both confirmed and questioned the theory in the intervening years. Some scientists said the original finding could be a flaw in the data.

Song, Richards, and colleagues' evidence is based on side-by-side comparisons of seismic waves from 18 pairs of earthquakes that were nearly identical in location and magnitude. They differed only in date, and such similarity diminishes the margin for error, National Geographic informs.

The tremors occurred in the South Sandwich Islands near Antarctica and were detected by seismometers near Fairbanks, Alaska. On their pole-to-pole journey, the seismic waves traveled through the Earth, some through the inner core.

"Essentially, the waves that traveled through the area outside the inner core?the crust, the mantle, the outer core?are all the same," Song said. "Only when they travel through the inner core are they different".

Song and Richards found that when earthquakes struck in nearly the same place years or decades apart, seismic waves generated by the later quakes arrived in Alaska a little sooner than they had the time before.

The only way this could be explained was if the inner core was spinning slightly faster than the rest of the planet. "We're saying that the inner core rotates just slightly faster. So in one day, it has rotated once plus a little bit more - in other words, it rotates just a little bit more each day than the crust and the mantle" co-author Paul Richards, of the Lamont-Doherty Observatory told BBC.

This so-called "superrotation" of the inner core is of the order of 0.3 degrees to 0.5 degrees each year. This means that in 900 years, the inner core would gain one full rotation on the rest of the planet.