Unraveling the Mechanisms of Fluid-Driven Fault Slip Propagation and Reactivation: An Integrated Experimental and Modelling Approach

• Applicant: Dr. Federico Pignalberi, Ph.D.
• Subject Area: Geophysics ; Geology ; Geotechnics, Hydraulic Engineering
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 584521200

Injecting fluids deep underground is essential for several key technologies that support the energy transition, such as geothermal energy production, underground storage of CO₂, and future hydrogen storage. These technologies rely on increasing fluid pressure in the subsurface to improve permeability and fluid circulation. However, fluid injection can also have unintended consequences: in some cases it triggers earthquakes. While many injections only cause slow, smooth fault motion without noticeable shaking, similar operations elsewhere have led to sudden and damaging seismic events. The physical reasons behind these contrasting responses are still not fully understood, limiting our ability to manage seismic risk reliably. This project aims to improve our understanding of how and why underground fluid injections can cause faults to slip in different ways. A central idea is that fluids do not spread uniformly along faults. Instead, fluid pressure migrates through the rock over time and interacts with irregular features on the fault surface known as asperities. These asperities are small but mechanically stronger areas that can locally resist or concentrate stress. Depending on how fluid pressure reaches and activates these zones, fault slip may remain slow and stable or transition into fast, seismic rupture. Understanding this interaction is essential to explain why earthquakes sometimes occur immediately after injection, sometimes with a delay, and sometimes not at all. To investigate these processes, the project combines controlled laboratory experiments with computer-based modelling. Large rock samples containing an artificial fault will be tested in the laboratory under realistic stress conditions. Fluids will be injected into the fault while advanced sensors continuously monitor pressure changes, rock deformation, and tiny earthquake-like signals that occur during slip. These experiments allow direct observation of processes that cannot be measured in the Earth’s subsurface, such as how pressure fronts migrate along a fault and how slip initiates at specific locations. The laboratory observations will then be used to develop and test physics-based models that simulate fault slip during fluid injection. By comparing model results with laboratory data and observations from underground injection experiments, the project will identify which mechanisms are robust and potentially transferable to real-world conditions. By clarifying the physical mechanisms behind fluid-induced fault reactivation, this research will contribute to safer and more reliable use of the subsurface. In the long term, it will help improve risk assessment and decision-making for underground energy technologies, supporting their sustainable deployment while reducing the likelihood of damaging induced earthquakes.

• DFG Programme: Position