Sébastien Merkel

This 2025 EGU General Assembly was held in Vienna, Austria, 27 April–2 May 2025. I and ERC HotCores members organized the session GD 8.4, Earth and Planetary cores, with several presentations from the project. See you next year!

New paper! On the Influence of Pressure, Phase Transitions, and Water on Large-Scale Seismic Anisotropy Underneath a Subduction Zone published in AGU's Geochemistry, Geophysics, Geosystems. This paper of J.K. Magali is one of the last results of the ANR-DFG TIMEleSS project. In this work, we investigate how subduction in the upper mantle and transition zone influences the alignment of minerals making up the mantle, which in turn, affects the speed and direction of seismic waves known as seismic anisotropy.

The annual meeting of the AGU attracts over 25,000+ scientists, educators, policymakers, journalists and communicators from over 100 countries in the broad field of Earth and space sciences. In December 2024, I was in Washington DC to attend the 2024 AGU Meeting and present the latest results of our European Research Council HotCores project.

New paper! Measurement bias in self-heating x-ray free electron laser experiments from diffraction studies of phase transformation in titanium, published in the Journal of Applied Physics recently. In this work, we focus on the physics of X-ray self-heating. X-ray heating is a common by-product of X-ray Free Electron Laser (XFEL) techniques that can affect targets, optics, and other irradiated materials. It is also useful in a new family of high pressure experiments that can reach the pressure and temperatures of planetary interiors. The work is a result of a collaboration of 31 laboratories over 7 countries and 3 continents, led by student O.B. Ball and R. S. McWilliams at the University of Edinburgh.

Participating to ICOTOM in Metz this week, the International Conference on Textures of Material, where world experts come to meet and discuss the latest advances in textures and microstructures of materials, with applications in multiple classes of materials, from metals to the deep Earth.

Yet another publication in two days! Zinc is a hcp structure metal, with a very large c/a ratio at ambient pressure, which then decreases and crosses √3 at ~10 GPa. As a consequence, twinning in zinc is unusual and can change in nature, from compressive to tensile, depending on the external pressure. Want to know more? Have a look at our ERC HotCores paper: Androgynous {10⁢-1⁢2} twin in zinc, published today in Physical Review Materials.

New publication from former PhD student Jeff Gay in Geophysical Research Letters: Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth's Lower Mantle! This paper is from the TIMEleSS project, in which we investigated anisotropy induced by phase transformation and deformation using multigrain X-ray crystallography. If you want to learn about pyrolite in the deep mantle, have a look at the paper!

Publication of former TIMEleSS post-doc John Keith Magali: Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow  in Geophysical Journal International. The papers focuses on a simple model of plate-driven corner flows and shows that, despite its simplistic formulation, it can explain first-order observations of mantle seismic anisotropy if one incorporates the effect of pressure on mineralogy and mineral plasticity models.

New publication in the Journal of Geophysical Research: Solid Earth. N. Hilairet writes about Stress balance in synthetic serpentinized peridotites deformed at subduction zone pressures. In this work, we analyze serpentinite rocks, which contain a variable amount of a weak minerals, including serpentine, and other stronger minerals and try to understand the effect of the percentage of the weak phase on the mechanical properties of the rock. The measurements are intended to help larger scale numerical models of interseismic processes that happen between earthquakes in subduction zones.

In case, you are wondering: you will not see me at the AGU Fall Meeting this year. I attended 22 out of the latest 26 AGU Fall Meeting. I felt that this year was a good one to take a break and not be travelling in December. Enjoy the meeting, I'm sure it will be great.