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The stress state is an important parameter in terms of both earthquake nucleation and rupture. Here, a new stimulation technique is proposed for Enhanced Geothermal Systems (EGSs), which have previously been burdened with a number of high‐profile incidences of induced seismicity. This stimulation technique pre‐emptively alters, or preconditions, the stress state before injection. This preconditioning is achieved through fluid production, such that the zone of reduced pore pressure around the well results in a stress‐ and fracture‐energy‐ barrier to potential nucleating and/or propagating ruptures near the point of injection. Using an existing 1‐D linear slip‐weakening model, it is shown how this methodology has the potential to either suppress the nucleation of dynamic events or halt their propagation. In particular, reducing the pore pressure around the region to be stimulated such that the residual shear stress rises above the in‐situ value of shear stress results in ultimately stable nucleation regimes. These results hold for injection times which are small compared to the required time of production, but this methodology results in nucleation lengths, or, analogously, stimulated areas, which are orders of magnitudes larger than those safely achievable without preconditioning. An example of how this approach may be applied in the field as well as other possible methods to achieve a preconditioned reservoir are provided. Both laboratory‐scale and meso‐scale testing of preconditioning are recommended to further constrain the applicability of this methodology for the creation of EGSs. Plain Language Summary: Enhanced Geothermal Systems (EGSs) are attractive due to their ability to provide potentially ubiquitous clean baseload power. However, they have been shown to be capable of inducing damaging and dangerous earthquakes, especially during and just after reservoir stimulation, a process enhancing the ease of fluid flow and required if these systems are to achieve sufficient energy fluxes. Interestingly, the state of stress is an important parameter for earthquake behavior. As previous studies have shown that engineers are able to influence the state of stress through their operations, a methodology is proposed that pre‐emptively alters, or preconditions, the stress field through the reduction of pressure before stimulation. The possible effects of this type of preconditioning are investigated by building upon a previously developed numerical model. The results indicate that pore pressure preconditioning may be able to delay the nucleation of an earthquake or stop an already‐nucleated earthquake from growing larger, meaning it may allow for reservoir stimulation at a reduced risk of induced seismicity. This methodology can be performed with a single well but requires large production times when compared to the time of injection. Laboratory‐scale and medium‐scale testing of this methodology are recommended before its application to a real EGS. Key Points: A stimulation strategy for Enhanced Geothermal System, called pore pressure preconditioning, is introducedPreconditioning results in early time dynamic rupture being contained or suppressed by the induced stress‐ and fracture‐energy‐ barrierWith sufficient preconditioning, the slipping patch must surpass the induced pressure barrier before nucleating runaway dynamic rupture [ABSTRACT FROM AUTHOR]

The transition from quasistatic slip growth to dynamic rupture propagation constitutes one possible scenario to describe earthquake nucleation. If this transition is rather well understood for homogeneous faults, how the friction properties of multiscale asperities may influence the overall stability of seismogenic faults remains largely unclear. Combining classical nucleation theory and concepts borrowed from condensed matter physics, we propose a comprehensive analytical framework that predicts the influence of heterogeneities of weakening rate on the nucleation length Lc for linearly slip‐dependent friction laws. Model predictions are compared to nucleation lengths measured from 2D dynamic simulations of earthquake nucleation along heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three instability regimes (local, extremal, and homogenized), each related to different nucleation scenarios, and that the influence of heterogeneities at a scale far lower than the nucleation length can be averaged. Plain Language Summary: Earthquakes occurs on fault. Faults are usually at rest, but they sometimes break and suddenly release a portion of the accumulated elastic energy during earthquake ruptures through radiated waves, which may harm populations and structures. Yet, the birth of earthquake (nucleation phase) is not an instantaneous process and may start with slow slip on the fault. Understanding precisely how this initial phase occurs is thus crucial in predicting earthquake motion. If geophysical models describe it well in an ideal case where the fault is made of the same exact material (homogeneous fault), the role of asperities, which are present from the millimetric rock grain scale to the kilometric tectonic plate scale, remains largely unclear. Here, we propose an extension of the nucleation theory to account for the role of each asperity scale in nucleating earthquakes. Our results show that an earthquake can be triggered by some seismogenic asperities as previously assumed, but that these "weak" asperities may not control its nucleation if they are small enough. In that case, we show that the birth of earthquakes along complex faults can be accurately studied within the traditional homogeneous nucleation theory. Key Points: The nucleation length of heterogeneous faults with multiscale asperities of weakening rate can be predicted for slip‐dependent frictionOur theory accounts for the transition in fault stability regimes from the traditional "weakest defect" theory to a homogenized behaviorOnly asperities larger than the nucleation length participate in the fault stability, while the influence of small asperities is averaged [ABSTRACT FROM AUTHOR]

Considering a semi-infinite crack propagating within a plane where the local fracture energy fluctuates due to the presence of microstructural heterogeneities, we emphasize the decisive influence of the material disorder on the effective fracture energy of the composite at a macroscopic scale. Through the use of large-scale numerical simulations of a crack interacting with tough inclusions of varying shape, we show how the disorder intensity and the inclusion geometry modify both quantitatively and qualitatively the toughening behavior with respect to the periodic case, where the inclusions are arranged in an ordered manner. This disorder-induced toughening is then rationalized using a theoretical homogenization framework borrowed from statistical physics. It ultimately allows to propose strategies for the design of disordered composites with improved crack growth resistance and tailored asymmetric fracture properties. [ABSTRACT FROM AUTHOR]