Geological carbon sequestration using basalts provides a solution to mitigate the high CO₂ concentration in the atmosphere. Due to the long timespan of the GCS, it is important to understand the long-term deformation of the reservoir rock. Here, we studied the creep of basalt with fluid presence. Our results show presence of fluid weakens the rock and promotes creep, while the composition only has a secondary effect and demonstrate that the governing creep mechanism is subcritical microcracking.

An experimentally deformed sample of Opalinus Clay (OPA), which is being considered as host rock for nuclear waste in Switzerland, was studied by electron microscopy to image deformation microstructures. Deformation localised by forming micrometre-thick fractures. Deformation zones show dilatant micro-cracking, granular flow and bending grains, and pore collapse. Our model, with three different stages of damage accumulation, illustrates microstructural deformation in a compressed OPA sample.

Properties of deformed rocks are frequently anisotropic. One of these properties is the travel time of a seismic wave. In this study we measured the seismic anisotropy of different rocks, collected in the Alps. Our results show distinct differences between rocks of oceanic origin and those of continental origin.

The construction of tunnels leads to substantial alterations of the surrounding rock, which can be critical concerning safety aspects. We use different mobile methods to assess the hydromechanical properties of an excavation damaged zone (EDZ) in a claystone. We show that long-term exposure and dehydration preserve a notable fracture permeability and significantly increase strength and stiffness. The methods are suitable for on-site monitoring without any further disturbance of the rock.

The competing modes of fault network development, including nucleation, propagation, and coalescence, influence the localization and connectivity of fracture networks and are thus critical influences on permeability. We distinguish between these modes of fracture development using in situ X-ray tomography triaxial compression experiments on crystalline rocks. The results underscore the importance of confining stress (burial depth) and fluids on fault network development.

Serpentinite, generated by the hydration of ultramafic rocks, is thought to be related to slow earthquakes at the subduction plate interface in the mantle wedge. We conducted friction experiments on brucite, one of the components of serpentinite, and found that wet brucite exhibits low and unstable friction under low effective normal stress conditions. This result suggests that wet brucite may be key for slow earthquakes at the subduction plate interface in a hydrated mantle wedge.

Fluids (like water or gases) within the Earth's crust often flow and interact with rock through fractures. The efficiency with which these fluids may flow through this void space is controlled by the width of the fracture(s). In this study, three different physical methods to measure fracture width were applied and compared and their predictive accuracy was evaluated. As a result, the mobile methods tested may well be applied in the field if a number of limitations and requirements are observed.

The injection of fluids (like wastewater or CO₂) into the subsurface could cause earthquakes when existing geological faults inside the reservoir are (re-)activated. To assess the hazard associated with this, previous studies have conducted experiments in which fluids have been injected into centimetre- and decimetre-scale faults. In this work, we analyse and model these experiments. To this end, we propose a new approach through which we extract the model parameters that govern slip on faults.

The strength of fault rock plays a central role in determining the distribution of crustal seismicity. We review laboratory work on the physics of fault friction at low shearing velocities carried out at Utrecht University in the past 2 decades. Key mechanical data and post-mortem microstructures can be explained using a generalized, physically based model for the shear of gouge-filled faults. When implemented into numerical fault-slip codes, this offers new ways to simulate the seismic cycle.

Coal is an important source rock for natural gas recovery, and its frictional properties play a role in induced seismicity. We performed experiments to investigate the frictional properties of bituminous coal, and our results show that the frictional strength of coal became significantly weakened with slip displacement, from a peak value of 0.5 to a steady-state value of 0.3. This may be caused by the development of shear bands with internal shear-enhanced molecular structure.

In this study, we conducted 3-D numerical simulations of fluid flow in synthetically generated fractures that statistically reflect geometries of naturally occurring fractures. We introduced a non-dimensional characterization scheme to relate fracture permeabilities estimated from the numerical simulations to their geometries in a unique manner. By that, we refined the scaling law for fracture permeability, which can be easily integrated into discrete-fracture-network (DFN) modeling approaches.

Rocks in fault zones can melt during earthquakes. The geometry and magnetic properties of such earthquake-melted rocks from Jämtland, central Sweden, show that they formed during Caledonian mountain building in the Palaeozoic. The small sample size (~0.2 cm³) used in this study is unconventional in studies of magnetic anisotropy and introduces challenges for interpretations. Nevertheless, the magnetic properties help shed light on the earthquake event and subsequent alteration of the rock.

Rock-forming minerals behave elastically, a property that controls their ability to support stress and strain, controls the transmission of seismic waves, and influences subsequent permanent deformation. Minerals are intrinsically anisotropic in their elastic properties; that is, they have directional variations that are related to the crystal lattice. We explore this directionality and present new ways of visualising it. We hope this will enable further advances in understanding deformation.

This study sheds light on the mineral-scale mechanisms controlling the progressive deformation of sheared amphibolites from the Oman metamorphic sole during subduction initiation and unravels how strain is localized and accommodated in hydrated mafic rocks at high temperature conditions. Our results indicate how metamorphic reactions and pore-fluid pressures driven by changes in pressure–temperature conditions and/or water activity control the rheology of mafic rocks.

Calcite twinning is a common deformation mechanism that mainly occurs at low temperatures. Twinning activation appears at a critical strength value, which is poorly documented and still debated. Temperature is known to influence twin thickness and shape; however, few studies have been conducted on calcite deformation at low temperatures. The goal of this work is to determine if thickness is mainly due to high temperatures and to establish the validity of a threshold twinning activation value.