You are here

27-10-2015 | Image: © Deuss et al. Regional Variation of Inner Core Anisotropy from Seismic Normal Mode Observations. Science (2010) vol. 328 (5981) pp. 1018-1020 | 2 mins read

The inner core of our planet was discovered more than 65 years ago and since then Earth scientists have been investigating to understand more about its precise structure and geodynamic properties. Many fundamental questions still remain unanswered. Supported by the ERC, Dr Arwen Deuss has achieved some impressive results in this field.

Life on Earth is possible thanks to its magnetic field that protects us from cosmic radiation and is generated by the core, which is the very central structure of our planet. Studying the composition and thermal state of the Earth’s deep interior is key to unraveling how its magnetic field works.

The Earth’s inner core is a solid ball the size of the Moon, made of iron and nickel, surrounded by an outer core of flowing liquid iron alloy. As no direct samples of the inner core, outer core and of the mantle can be taken, our knowledge of their structure and properties relies on seismology, the only tool that allows us to “see through” the Earth. Seismometers measure the waves generated by earthquakes and these data are interpreted to evaluate the Earth’s composition, density and velocity.

In her project, Dr Deuss coupled seismic observations of whole Earth oscillations, which make the Earth ring like a bell, with expertise in fluid dynamics and mineral physics. Her team developed pioneering tools to focus on some specific deep parts of our planet, something which had not been possible before due to lack of appropriate theory. Applying this novel theory and analyzing data from large earthquakes all around the globe - including the 2011 devastating seismic event in Japan - the team made a new comprehensive model of the inner core leading to several exciting discoveries.

Dr Deuss’ work has shown that the top of the inner core is divided into two hemispheres with very sharp boundaries. They are so different that they might be the equivalent of the continental and oceanic regions on the Earth’s surface - limiting the phenomenon of inner core superrotation to less than one degree per million years. They also found that a few weight percent of light elements, such as silicon
or oxygen, needs to be present in the solid inner core in order to explain their observations of seismic attenuation anisotropy. These observations suggest that the geodynamic process at the origin of Earth’s inner core is much more complex than initially thought. The inner core heterogeneity might also be linked to places where the magnetic field of the Earth is stronger or weaker.