Stanford University

Francois Renard, University of Oslo, Dynamics of Precursors When Approaching system-Size Failure in

Thursday, Mar 12, 2020 12:00 PM
Mitchell Building, Room 350/372
Geophysics Department


Francois Renard

 Department of Geosciences, University of Oslo

4D X-ray Tomography Experiments and Machine Learning Reveal the Mechanisms of Brittle Failure in Rocks

Date: Thursday, March 12, 2020

Location:  Mitchell 350/372

Time:  12:00 pm - 1:15 pm

Host:  Tiziana Vanorio

Microscale heterogeneities influence failure mechanisms in rocks of the Earth’s crust and control natural hazards such as rock falls, landslides, earthquakes, and volcanic eruptions. The dynamics of brittle deformation prior to macroscopic instability in rocks is therefore critical to understanding the earthquake preparation process and failure. To track the microstructural changes in rock samples when loaded until failure, a novel experimental technique enables to couple dynamic X-ray microtomography imaging with a triaxial deformation apparatus [1] and data are analysed using machine learning techniques [2].

We imaged the route to failure in rock specimens using in-situ dynamic X-ray microtomography and digital volume correlation analysis. The evolution of microfracture opening, closing and shearing, leading to system-size failure, is documented with unprecedented spatial resolution. We quantified how brittle failure in conditions of the Earth’s crust is the result of the coupling between microfracture growth, opening, coalescence and closing, as well as left-lateral shear displacement and right-lateral shear along microfractures. Analysis of these data shed new light on the nucleation of faults in rocks because at the onset of failure damage was almost entirely connected in three-dimensions, with most of the fracture porosity contained in a fracture network that spanned the entire volume and evolved into a geometrically complex three-dimensional fault zone.

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