The first concept about the inner core of earth was developed by Inge Lehmann in 1936. Researchers are consistently doing scientific researches to explore more unknown facts about the interior structure of the earth.


As per some recent study, the chronological change of seismic phases is taking place in the centre of the earth's interior with a quality webform doublets. But the actual nature of this temporal variation of seismic phases of inner core of the earth, nevertheless, is agitated.

The study is being carried forward by joint effort of Yi Yang, Department of Geology at University of Illinois, the lead author of the research, and Xiaodong Song, Institute of Theoretical and Applied Geophysics, School of Earth and Space Sciences, Peking University, the co-author of this research.

It is not quite clear to the scientists about the functionality of the magnetic field generator of the earth, till date. But they have made some assumption about it, that the fact is anyhow related to the potentiality at the Lehmann discontinuity area, situated between the outer core and inner core of the earth.

Xiaodong Song has stated that,
In 1996, small but systematic change of seismic waves passing through the inner core was first detected by our group, which we interpreted as evidence for differential rotation of the inner core relative to the earth's surface. However, some studies believe that we interpret as movement is instead the result of seismic waves reflecting off an alternately enlarging and shrinking inner core boundary, like growing mountains and cutting canyons.

What does the study reveal ?

For this study, researches have used and analysed datasets of seismic waves of doublets (that means repeating earthquakes which occur in the same spot or location over a span of time) at a specific geographic location. Using these datasets, they succeeded to reckon between two category of seismic gestures. One is which occurs based on the localised differentiation in relief, and the another is that which changes because of the movement and rotation of the earth.

Graphic representation of earth's inner core and the seismic phase

Their study reveals that, sometimes seismic waves penetrate or diffuse through iron materials of the interior body, specifically in the inner core area and change after a certain time period. This could occur only if the inner core is in motion.


The research depicts that temporal changes occur mostly from the interior rather than the inner core boundary. It has presumed that there is a rotation rate of about 0.05° to 0.1° per year with a little decadal fluctuation at the inner core.

Song mentioned that,
Importantly, we are seeing that these refracted waves change before the waves bounce-off the inner core boundary, implying that, the changes are coming from inside the inner core.

He also said,
This precise arrival time analysis, an extensive collection of the best quality data and careful statistical analysis performed by Yang, are what give this study its power. This work confirms that the temporal changes come usually, if not all, from the body of the inner core, and the idea that inner core surface changes are the sole source of the signal changes that can now be ruled out.

According to Yi Yang,
What makes our analysis different is our precise methods of determining exactly when the changes in seismic signals occur and reach at various seismic stations across the globe. We use a seismic wave that did not reach inner core as a reference wave in our calculations, which sort out a lot of ambiguity.

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