The reverberations from earthquakes as they bounce back and forth through the centre of Earth have revealed new details about the structure of the planet’s inner core, according to a study published in Nature Communications. To better understand the inner core’s structure, researchers used multiple seismometers to examine how seismic waves are distorted as they pass through the solid ball of iron nickel at Earth’s heart.
To detect these oscillations, researchers recorded the waveforms at close to the original site of the earthquake and at the antipode —the direct opposite position on the surface of Earth. This enabled them to look at the multiple journeys through Earth’s centre. Each reverberation takes around twenty minutes to cross from one side of the planet to the other, and the seismometers recorded up to five bounces from a single event.
They found that the waves travelled differently through the innermost inner core — which they estimate to be around 650 kilometres thick — than through the outer part. Waves passing through the innermost part of the core slowed down in one direction, whereas waves passing through the outer layer slowed down in another direction.