Can a volume reduction alone trigger faulting deep inside the Earth? In “Transformational Faulting: The Case of Quartz-Coesite”, Giulia Mingardi and colleagues deformed quartzite at high pressure and temperature at beamline P61B (PETRA III, DESY), combining synchrotron X-ray diffraction and acoustic emission monitoring. When the quartz-to-coesite transformation was slow, acoustic emissions and microstructures revealed localised faulting. When it was fast, deformation was distributed. The results show that the volume change alone is enough to trigger transformational faulting, extending the range of mineral reactions that may generate deep and intermediate-depth earthquakes.

Read the paper: https://doi.org/10.1029/2026GL124806