Here we report the raw data of the friction experiments carried out on basalt-built simulated faults defined by rock-on-rock contacts and powdered gouge. The experiments were specifically designed to investigate the role of fault microstructure on the frictional properties of basalts and the fault slip stability, and were conducted with the rotary-shear apparatus (SHIVA) and the biaxial deformation apparatus (BRAVA), hosted at the National Institute of Geophysics and Volcanology (INGV) in Rome.
Simulated faults were sheared at constant normal stress from 4 to 30 MPa. In SHIVA experiments, we deformed samples at constant slip velocity of 10 μm/s up to 56 mm net slip. In BRAVA tests we performed a sequence of velocity steps (0.1 to 300 μm/s), followed by slide-hold-slide tests (30-3000 s holds; V=10 μm/s slides).
Our main results highlight the frictionally strong nature of basalt faults and show opposite friction velocity dependence upon the velocity upsteps: while fault gouges exhibit velocity weakening behavior with increasing normal stress and sliding velocity, bare rock surfaces transition to velocity strengthening behavior as we approach higher slip velocities. The experiments setup and data are further described in the manuscript “Frictional properties of basalt experimental faults and implications for volcano-tectonic settings and geo-energy sites” to which these data are supplementary material.
We investigated the frictional properties of simulated fault gouges derived from the main lithologies present in the seismogenic Groningen gas field (NE Netherlands), employing in-situ P-T conditions and varying pore fluid salinity. Direct shear experiments were performed on gouges prepared from the Carboniferous Shale/Siltstone underburden, the Upper Rotliegend Slochteren Sandstone reservoir, the overlying Ten Boer Claystone, and the Basal Zechstein anhydrite-carbonate caprock, at 100 ºC, 40 MPa effective normal stress, and sliding velocities of 0.1-10 µm/s. As pore fluids, we used pure water, 0.5-6.2 M NaCl solutions, and a 6.9 M mixed chloride brine mimicking the formation water. Our results show a mechanical stratigraphy, with a maximum friction coefficient (µ) of ~0.65 for the Basal Zechstein, a minimum of ~0.37 for the Ten Boer claystone, ~0.6 for the reservoir sandstone, ~0.5 for the Carboniferous, and µ-values between the end-members for mixed gouges. Pore fluid salinity had no effect on frictional strength. Most gouges showed velocity-strengthening behavior, with little effect of pore fluid salinity on (a-b). However, Basal Zechstein gouge showed velocity-weakening at low salinities and/or sliding velocities, as did 50:50 mixtures with sandstone gouges, tested with the 6.9 M reservoir brine. From a Rate-and-State-Friction viewpoint, our results imply that faults incorporating Basal Zechstein anhydrite-carbonate material at the top of the reservoir are the most prone to accelerating slip, i.e. have the highest seismogenic potential. The results are equally relevant to other Dutch Rotliegend fields and to similar sequences globally. The data is provided in a .zip folder with 29 subfolders for 29 experiments/samples. Detailed information about the files in these subfolders as well as information on how the data is processed is given in the explanatory file Hunfeld-et-al-2017-Data-Description.pdf