Fluid-induced rupture experiment on Fontainebleau sandstone:: Premonitory activity, rupture propagation, and aftershocks

[1] A 14% porosity Fontainebleau sandstone sample ( diameter = 40 mm, length = 88 mm) was loaded triaxially, under 100 MPa confining pressure and 240 MPa differential stress. In drained conditions and under constant load, pore pressure ( water) was raised until failure was triggered. During the experiment, elastic wave velocities and permeability were monitored while more than 3000 Acoustic Emissions (AE) were located prior and after failure. AE locations show that macroscopic fracture propagated from a large nucleation patch at speeds comprised between 0.1 and 4 m/s. Number of AE hits per second followed Omori's law, with exponents of 0.92 and 1.18 pre- and post-failure respectively. No quiescence was observed post failure, except where rupture initially nucleated from. Fast depressurization of the pore space induced secondary aftershocks located within the fracture plane, possibly indicating a heterogeneous fault geometry after rupture, of lower permeability, that compacted during the release of pore pressure.