A revolution in rock physics: 4D imaging

The ability to establish rheological and fluid‑transport laws in the lithosphere for use in geomechanics and geodynamics models depends on laboratory experiments validated by field observations. In experiments, a key challenge is reproducing the pressure, temperature, and fluid‑chemistry conditions found at depth while acquiring sufficient information inside rock samples to understand and generalize the detailed mechanisms of rock deformation and chemical evolution. Over the past fifteen years, breakthroughs in rock physics have been enabled by experiments conducted at large user facilities such as synchrotron and neutron sources. From shallow subsurface fluid–rock interactions to slow and fast rupture and down to the brittle–ductile transition at the base of the seismogenic zone and deep earthquakes, it is now possible to image geological processes in 4D (3D + time) with unprecedented spatial and temporal resolution in samples large enough to be representative of lithospheric processes.

Recent experiments demonstrate how a porous rock can become clogged and store carbon dioxide, including direct imaging of fluid mixing and precipitate formation, how porosity can be generated at the brittle–ductile transition, altering our view of fluid transfer at the base of the seismogenic zone, and how damage nucleates before and during earthquakes. These findings highlight the importance of dynamic porosity — which controls fluid transport and deformation — and call for integrating more widely this property into large‑scale models of Earth’s crust dynamics.