Injection‐induced seismicity is thought to be due primarily to increase in fluid pore pressure, which reduces the shear strength of a nearby fault. We address the modeling and prediction of the hydromechanical response due to fluid injection, mainly as wastewater disposal. We consider the full poroelastic effects, including the changes in porosity and permeability of the medium due to changes in local volumetric strains. Our results consider effects of the fault architecture (low‐permeability fault core and anisotropic high‐permeability damage zones) on the pressure diffusion and the fault poroelastic response. We show that the high‐permeable damage zone, the poroelastic response, and the permeability evolution can accelerate the pore pressure diffusion process during and after wastewater injection. By studying a geologically based model of the Guy‐Greenbrier fault and of the earthquake sequence induced along it in Arkansas, United States, from October 2010 to July 2011, we show that the existence of highly permeable damage zones facilitates the pressure diffusion and results in a sharp increase in pore pressure at levels much deeper than the injection wells, while the anisotropic permeability in the damage zone can act as a barrier to cross‐fault fluid flow. Furthermore, by computing the change ΔCFS of Coulomb failure stress, our simulations show that ΔCFS increases starting from the top of the Guy‐Greenbrier fault and then propagates toward greater depth and toward the southwest direction, which is consistent with the seismicity migration.

Antarctic mass balance and contribution to sea level rise are dominated by the flow of ice through narrow conduits called ice streams. These regions of relatively fast flow drain over 90% of the ice sheet and generate significant amounts of frictional heat at the ice stream margins where there is a transition to slow flow in the ridge. This heat can generate temperate ice and a sharp transition in flow speed between the stream and the ridge. Within zones of temperate ice, meltwater is produced and drains to the bed. Here we model the downstream development of a temperate zone along an ice stream shear margin and the flow of meltwater through temperate ice into a subglacial hydrologic system. The hydrology sets the basal effective pressure, defined as the difference between ice overburden and water pressure. Using the southern shear margin of Bindschadler Ice Stream as a case study, our model results indicate an abrupt transition from a distributed to channelized hydrologic system within a few ice thicknesses of the point where the temperate zone initiates. This transition leads to a strengthening of the till due to reduced pore pressure because the water pressure in the channel is lower than in the distributed system, a potential mechanism by which hydrology can prevent lateral migration of shear margins.

Micro‐crack density, porosity, and permeability in fault damage zones play an important role in the pore fluid diffusion process. During long‐term earthquake cycles, those properties change with time as a result of either physical damage or chemical/physical healing. Hence, the evolution of permeability can affect the recurrence of earthquakes by either delaying or accelerating the weakening of the fault core through controlling the pore pressure distribution and changing the effective normal stress. In this study, we use a single degree of freedom spring slider analog fault model to simulate the earthquake sequences, considering permeability as a decreasing function of the effective normal stress and thus an increasing function of pore pressure; we also examine its evolution resulting from coseismic damage and interseismic healing. Our simulation results show that different permeability evolution, controlled by various physical conditions, could result in a variety of fault slipping histories, which demonstrates the importance of incorporating the permeability evolution into earthquake modeling, especially when assessing the long‐term effects.

The composition of hydraulic fracturing (HF) fluid poses risks to human health and the environment by impacting drinking water sources. Fracturing fluid recovery rate is highly variable, and the fact that a high percentage of the injected HF fluid is not produced back to the surface in some areas raises questions about its fate and possible migration into aquifers. In this paper, the composition of the HF fluid and related toxicity are described, along with insights about the environmental impact linked with HF fluid, synthesized spill data, main factors affecting the flow-back ratio, and induced seismicity related to HF activities. The environmental and health hazards posed by HF fluid are concerning due to the high concentration of toxic chemicals, the limited data on toxicity, the high probability of spills, and the reported cases of aquifer contamination. Furthermore, low load recovery values (10%–50 %) suggest that a significant volume of fracturing fluids may remain in the subsurface, thereby potentially increasing the likelihood of fluid migration towards drinking water sources under certain conditions. Hence, the fate of HF fluid is explained by establishing correlations between fluid flow (i.e., flow-back and migration to the subsurface) and different operation and formation parameters. For example, a negative correlation was detected between HF fluid recovery and shut-in period, fracture network complexity, and induced seismicity, while a positive correlation was observed between HF fluid migration speed and permeable pathways. Moreover, it is shown that the main handicap in assessing related risks is the scarcity of disclosure and monitoring data. Consequently, future work must focus on imposing strict disclosure and incident-reporting regulations, and more publications should be dedicated to inspecting the composition and impact of HF fluid.