Preliminary work for experiments on inner core attenuation

The Earth’s inner core is made of a solid iron alloy. Seismic observations suggest a structure and an anisotropy which leads to variations in both the velocity and the attenuation of the seismic waves. Attenuation is the loss of energy during the propagation of the seismic waves. Whether this attenuation arises from intrinsic properties of the iron alloys or extrinsic origins remains an open question. In this context, studying attenuation in metallic alloys could help improving our knowledge about the physical properties and the geodynamic of the inner core.

Different sources of attenuation exist in the core: extrinsic and intrinsic sources. The first one is linked to external environment that impact the wave propagation, such as scattering or heterogeneities. Intrinsic sources are related to the properties of the material itself. This work focuses on the latter and particularly on the anelastic relaxation, which is one of the source of internal friction.

In this work, we are re-investigated these problems to understand attenuation mechanisms in metals at high temperature. The experiments are conducted on a dynamic mechanical analysis (DMA) instrument with control of temperature and oxygen fugacity albeit at ambient pressure. Thus, we use an analogous material which presents similar crystallographic structure and is expected to behave like the inner core.

Here, we will present the first tests realized with variable frequency and constant temperature and discuss the future steps of the project.