Back to the core: a hard globe inside planet Earth

If, on the other side of the planet a powerful earthquake occurs, light seismic vibrations from that shock can be measured on our side of the planet. The whole planet vibrates for a little while afterwards, as if it was a kind of cosmic bell. Those vibrations can theoretically prove the presence of a hard core in the interior of the Earth: the hard core generates a “transversal” wave, a different type of wave than those transmitted through the liquid “cloak” of the planet.
Arwen Deuss was the first person in the world to differentiate a transversal wave from the cacophony of the other waves. She did it by combining seismological measurements from many measuring stations via smart computer programmes. Numerous small waves added up to one big one. It was the first proof that there is a thick globe in the heart of the liquid cloak, filled with metal and approximately the same size as the moon.
Since then, more has become clear about this hard core. For example it is not of homogeneous composition: there are more mineral rocks in some parts than others. Perhaps that explains why at the Earth’s surface magnetic fields are not harmonious, and our compasses sometimes exhibit fluctuations.

Deuss: “In seismic tomography we make images of the Earth’s cloak using the seismic waves which follow earthquakes or large explosions. From the pattern in which waves are attenuated, delayed or change direction, we can in theory reconstruct what is under us. Unfortunately geologists often focus on the short seismic waves, vibrations that can be measured shortly after an earthquake. These teach us a lot about the outer shell of the Earth, but I especially want to know what is happening deep inside. What changes and moves the rock there? Where does it heat up, where does it cool down? Where is it hard, where does it begin to melt? Where is water, where are minerals? The Ammodo KNAW Award enabled me to develop new methods for studying the long-standing seismic waves, which encompass the entire earth. Even days after a major earthquake they continue to resonate, like a church bell. If we can properly analyse these waves, we hope to learn more about what is inside the planet”.