It is a travel into the depths of our planet that is awaiting us, more exactly into its mantle, this intermediate layer between Earth’s core and crust. The mantle represents a little bit more than 80% Earth’s volume and around 65% mass. All this to say it is an important topic for researchers, such as Barbara Romanowicz from the Institut de physique du globe de Paris (IPGP) and the University of California, Berkeley. Her objective: A better understanding of the internal structure and dynamics of Earth’s mantle, the movements of which explain plate tectonics and continental drift. 

Here, the use of high performance computing is paramount: “It is a question of imaging as accurately as possible the interior of Earth’s mantle, from its top to its lower layers, by using seismic waves that propagate inside our planet”, she explained.

To achieve this, the research team has developed a global model of the entire Earth’s mantle. And it has been a tremendous work: “10 years were necessary to build it but it is now the first of the kind”, she underlined.

Thanks to their model, Barbara Romanowicz and her team have confirmed that “hotspots” volcanism is due to columns of hot material rising from the depths of the mantle, at the boundary with Earth’s core and is not directly related to the diverging or converging motions of tectonic plates. Scientists have also been able to link these columns of hot material to twenty-some hot volcanoes around the world.  l

These calculations have mobilized GENCI’s resources (400,000 core hours on Occigen) and also those of the National Energy Research Scientific Center (NERSC) in the US. They are a first step towards the development of a “numerical telescope” which will be used by the research team to zoom into some particular areas of Earth’s mantle.



Vertical cross sections across the Earth's mantle in the vicinity of prominent hotspot volcanoes (indicated by green triangles). The cross-sections show lateral variations of shear wave velocity (in percent of global average at each depth), which is roughly a proxy for temperature (hotter regions are manifested by lower than average shear velocities, i.e. they appear in red).  Broken lines are drawn at depths of 400, 660 and 1000 km. Until recently, the presence of plume-like structures beneath major hotspots was suggested, but the depth extent of these plumes was not unequivocally resolved. Such vertically oriented plume-like low velocity conduits are present under nearly 20 major hotspots in the world. © French & Romanowicz, Nature, 2015