Mechanical data of rotary shear experiments in bituminous dolostones

Mirror-like Surfaces (MSs) are ultra-polished fault surfaces widespread in carbonate seismic terrains, but their formation process is still debated. We deformed gouge samples from exposed fault surfaces hosted in bituminous dolostone rocks in a rotary shear apparatus (SHIVA) at seismic slip rates (1 m/s). By changing the water availability (water-pressurised and room-humidity conditions) and the organic matter/dolomite content (> 35%, dark gouge DG; < 30% bright gouge BG) we investigated the mechanical behaviour leading to MSs formation in fault gouges. We run tests at 15 MPa effective normal stress, 2 MPa confinement and 1 MPa pore pressure for the water-pressurised experiments and a total displacement of 0.13 m. Mirror-like fault surfaces were obtained in all successful experiments; mirrors were more developed under room-humidity conditions. Bituminous dolostones under room-humidity conditions had a slip neutral behaviour with a low friction (0.3). Bituminous dolostones under water-pressurised conditions showed a slip weakening behaviour with an initial peak effective friction μp = 0.65, followed by a drop to effective friction μss DG than in BG (i.e., μss of 0.25 vs 0.28). Future work will focus on the microstructural analysis of the experimental products and the investigation of the slip behaviour of bituminous dolostones at sub-seismic slip rates for a complete study of the slip behaviour spectra.

This publication results from work conducted under the national open access action at SHIVA (Slow to High Velocity Apparatus) - HP-HT laboratory of experimental Volcanology and Geophysics (INGV, Roma 1 section) supported by WP3 ILGE - MEET project, PNRR - EU Next Generation Europe program, MUR grant number D53C22001400005.