Abstract

Catastrophic failure is the end result of progression and localisation of damage towards brittle failure on a variety of system scales in the Earth. However, the factors controlling this evolution, and that of the resulting seismicity, are not well constrained.  We address the question of how to relate the two, and the extent to which they can be controlled by feedback on the seismicity rate in a scale model experiment on a small rock sample deformed in a synchrotron. We image the underlying damage using x-rays and detect acoustic emissions, and show how they change during localisation, from distributed tensile cracking to a localised shear band containing a mixture of tensile cracking, grain rotation, and grain boundary shear, with shear becoming increasingly dominant and ultimately frictional sliding on a contiguous fault.  We confirm that using continuous servo-control based on acoustic emission event rate not only slows down deformation compared to standard constant strain rate loading, but also suppresses events of all sizes, including extreme events. We use this evolution to develop a mixture model for the stress history from damage mechanics, and find it is independently consistent with the observed stress history and acoustic emission statistics. Our results imply that including seismic event rate control may improve risk management of induced seismicity compared to feedback on the maximum magnitude alone.