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Earthquake reverberations reveal new insights into Earth’s inner core structure

A study published in Nature Communications has shed new light on the structure of Earth’s inner core by examining the reverberations caused by earthquakes bouncing back and forth through the planet’s center. The research has been able to confirm the existence of distinct layers within the inner core, which have previously been difficult to characterize.

To better understand the structure of the inner core, researchers employed multiple seismometers to measure the distortion of seismic waves as they passed through the solid iron-nickel core. The waves were recorded at the original site of the earthquake and at the opposite position on the surface of Earth, known as the antipode, enabling researchers to study the multiple journeys through Earth’s center.

By using a technique called stacking, where waveforms from a single event are combined to build a more detailed picture of the distortion, the researchers were able to identify differences in the way the waves traveled through the innermost and outer parts of the inner core. The study estimates the thickness of the innermost layer to be around 650 kilometers, and suggests that the iron crystals in this layer are likely organized differently than in the outer layer.

According to co-author Hrvoje Tkalčić, a geophysicist at the Australian National University in Canberra, the Earth oscillates like a bell after a large earthquake, for days rather than hours. While the technique of using stacked measurements is routinely used in minerals exploration, it is not commonly used in geophysics.

The study’s findings will help in understanding how Earth’s solid inner core formed and what role it played in shaping the planet’s magnetic field. The process of inner core formation is thought to have begun somewhere between 600 million and 1.5 billion years ago. Geophysicist Vernon Cormier at the University of Connecticut in Storrs called the study important, saying that it offers a measurement of Earth’s innermost section that was difficult to achieve, requiring the enhancement of weak seismic waves recorded at very long distances.

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