Prof. Francois Renard

Biography

François Renard has extensive expertise in experimental and theoretical geophysics and geochemistry. In the mid-1990s, at Indiana University, he developed theoretical models of rock deformation. In the early 2000s, he started a highly productive collaboration with physicists and geologists at the former Centre of Excellence for the Physics of Geological Processes at the University of Oslo and at the University Joseph Fourier in Grenoble. During this time, he researched the mineralization of carbon dioxide into carbonates, specifically in the context of geological carbon storage. He also studied how fluids circulate in the Earth’s crust and couple with rock deformation. In the 2010s, he initiated a partnership with the European Synchrotron Radiation Facility and several other large user facilities, leading to the development of rock deformation and fluid flow apparatuses capable of replicating conditions in Earth’s crust. These methods—4D (space + time) X-ray or neutron tomography—have been a groundbreaking advancement in rock physics and geomechanics. Since joining the University of Oslo in 2016, he has developed studies at the interface between geophysics and the physics of porous media, in the cross-disciplinary geoscience-physics Njord Centre, which he is currently leading.

Introduction of the Lecture

Imaging rock failure reveals fracture coalescence as the main driver of laboratory earthquakes

How earthquakes start, propagate, and stop remains an open question in geosciences. In particular, the nucleation process, by which precursory deformation may lead to system-size, earthquake-like failure, is critical. Although such precursory signals are often detected in experiments where rocks are brought to failure under compression, field observations show that precursory signals are observed for some earthquakes but not for others. One possible explanation is that some of these precursory signals are non-seismic, corresponding to slow sliding or volumetric deformation, and are therefore difficult to detect with seismological monitoring. To image this precursory activity under laboratory conditions, a recent experimental technique, 4D (3D + time) X-ray synchrotron imaging, allows monitoring of the deformation that accumulates in a rock sample as it approaches failure.

Here, I present experimental evidence of how precursory activity before a laboratory earthquake organizes itself. The initial precursory activity is related to the nucleation of microfractures and their growth until they begin to interact mechanically and follow scaling laws. The final approach to failure is due to the coalescence of microfractures, which provides an additional criterion for assessing the proximity of system-size failure in rocks.