The world-first conclusions - which used a new mathematical method to interpret earthquake waves from five decades - found the 1980s was a slow decade for inner core movement, while recent years had seen the strongest speed-up.

Associate Professor Hrvoje Tkalcic said the five-person team's research analysed the solid inner core rotations relative to the Earth's mantle, which lies between the core and the Earth's crust.

''The mean or average rate [of rotation] faster than the mantle is only a fraction of a degree a year - 0.25-0.48 of a degree,'' he said.

''But what we found on that mean … rotation is there is another pattern that is superimposed on that - decadal fluctuations - and these fluctuations can be one degree or even faster than the mantle.

Dr Tkalcic said the research analysed 24 pairs of earthquakes with similar waveforms dating from 1961 to 2007, and explained discrepancies in previous studies covering much shorter periods.

''We found that compared with the mantle, the inner core was rotating more quickly in the 1970s and 1990s, but slowed down in the 80s,'' he said.

''The most dramatic acceleration has possibly occurred in the last few years, although further tests are needed to confirm that observation.''

The earthquakes used were all of a 6.0 magnitude or above, occurred around the South Sandwich Islands in the southern Atlantic Ocean, and were measured at an Alaskan station.

By comparing earthquakes' waveforms that are almost identical, but differ because of the speed at which they travel through the inner core, the researchers were able to reconstruct a history of the inner core's rotation.

Dr Tkalcic said the differential rotation of the earth's inner core is affected by a strong magnetic field and the gravity from the presence of the mantle, which scientists believe makes up about 84 per cent of the planet's volume.

The Croatian-born academic said the waves travelled most quickly through the inner core as it was the densest part of the planet.

''[They moved at] slightly more than 11 kilometres a second near the inner core, whereas where they are generated in the upper mantle, that speed is more in the order of 5-6kms/s,'' he said.

Dr Tkalcic - who worked with a colleague and three students from the Seismology and Mathematical Geophysics group of the ANU's Research School of Earth Sciences - said the research could help lead to a better understanding of the dynamics of the planet.

''We study the inner core because it is there, because we try to understand how our planet was created, planetary evolution,'' he said.

''There are no dramatic consequences [of differing rotation rates] for people on the surface, but it is crucial for scientists studying our planet.''

Dr Tkalcic said the new experimental evidence placed Australian geoscience at the ''forefront'' of this research area, but better global funding for ocean-floor measuring stations would help future advancements.

''We invest a lot [into] the space industry, but it would be nice to have more research to investigate what we have beneath our feet,'' he said.