# Understanding post-injection seismicity: Causes and mechanisms of trailing earthquakes in Enhanced Geothermal Systems

Auregan Boyet, Silvia de Simone, Frédéric Cappa, Víctor Vilarrasa

► To cite this version:

Auregan Boyet, Silvia de Simone, Frédéric Cappa, Víctor Vilarrasa. Understanding post-injection seismicity: Causes and mechanisms of trailing earthquakes in Enhanced Geothermal Systems. Renewable and Sustainable Energy Reviews, 2025, 223, pp.116055. 10.1016/j.rser.2025.116055. hal-05154504

HAL Id: hal-05154504

https://hal.science/hal-05154504v1

Submitted on 9 Jul 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# Understanding post-injection seismicity: Causes and mechanisms of trailing earthquakes in Enhanced Geothermal Systems

Auregan Boyet<sup>a, *, 1 ID</sup>, Silvia De Simone<sup>b</sup>, Frédéric Cappa<sup>c, d ID</sup>, Víctor Vilarrasa<sup>a, ** ID</sup>

## ARTICLE INFO

### Keywords:

- Induced seismicity

- Enhanced geothermal systems

- Stimulation

- Fault reactivation

- Permeability enhancement

- Triggering mechanisms

- Renewable geothermal energy

## ABSTRACT

Enhanced Geothermal Systems (EGS) employ fluid injection for both reservoir stimulation and circulation, a practice that may sometimes induce earthquakes. Paradoxically, numerous EGS projects have observed the occurrence of the largest-magnitude earthquake (LME, 1.6 < *M* < 5.5) after injection cessation, posing a significant challenge for the development of geothermal power plants. This paper aims to examine the cases of post-injection LME observed in EGS, and provide a detailed understanding of the coupled mechanisms responsible for seismic activity during and after fluid injection. We report the mechanisms that have been hypothesised for different cases of LME emerging in the post-injection phase of EGS. The analysis of post-injection LME cases reveals two types of seismicity, early and late, differentiated by the time at which pore pressure changes become negligible, i.e., a post-injection time longer than the injection time. Notably, we remark that, for most cases of early post-injection high-magnitude earthquakes, the primary triggering mechanisms involve pore pressure diffusion, thermal effects, poromechanical stress relaxation and static stress transfer resulting from seismic fault slip. Conversely, prolonged fluid injections could lead to the gradual accumulation of stress on faults, mainly due to aseismic slip, causing late post-injection LME. Furthermore, recent studies have also demonstrated the importance of the initial fault stress criticality in influencing the post-injection behaviour of fault aseismic slip and trailing seismicity. Finally, we present recent efforts devoted to develop effective methodologies for mitigating induced seismicity, and the current research perspectives aimed at forecasting and minimizing seismic activity associated with EGS.

## 1. Introduction

Geothermal systems are considered a key solution to drive the energy transition towards net-zero carbon emissions because geothermal energy is a secure, clean and renewable source of energy as it can be produced without intermittency, pollution and carbon emissions [1–3]. Geothermal energy utilizes the heat from the planet’s interior, which is virtually inexhaustible on human timescales. This energy is primarily harnessed in regions where the Earth’s crust is relatively thin, facilitating the transfer of heat to the surface through rock and fluids [4]. Such regions usually exceed the mean Earth geothermal gradient of 30 °C/km. Depending on the thermal conditions and the reservoir depth,

geothermal energy is envisioned for heating and/or for power-plant development. The latter requires high temperature (T > 150 °C), which can be found in volcanic systems and in deep crystalline rock, and occasionally at depth in sedimentary rock [4].

In deep crystalline rock, the main limitation for effective heat production is usually its low permeability, implying low fluid-circulation capacity. To overcome this limitation, Enhanced Geothermal Systems (EGS) are developed by engineering the potential reservoir to enhance the permeability, facilitating fluid circulation and heat exchange between the injection and the production wells through an optimal generation of connected, high-permeability fracture/fault network [5]. The goal of the EGS stimulation is to reach an efficient circulation aimed to

<footnote><sup>a</sup> Global Change Research Group (GCRG), IMEDEA, CSIC-UIB, Esporles, Spain</footnote>

<footnote><sup>b</sup> Institute of Environmental Assessment and Water Research, Spanish National Research Council (IDAEA-CSIC), Barcelona, Spain</footnote>

<footnote><sup>c</sup> Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Géoazur, Sophia Antipolis, France</footnote>

<footnote><sup>d</sup> Institut Universitaire de France, Paris, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>** Corresponding author.</footnote>

<footnote>E-mail addresses: auregan.boyet@ensta.fr (A. Boyet), victor.vilarrasa@csic.es (V. Vilarrasa).</footnote>

<footnote n="1">¹ now at IMSIA (UMR 9219), CNRS, EDF, CEA, ENSTA Paris, Institut Polytechnique de Paris, Palaiseau, France.</footnote>
generate ~20 MW<sub>e</sub> for a period of 20–40 years [6]. This engineered enhancement of permeability is achieved by means of forced injections, such as hydraulic or acid stimulations. The first EGS projects were initiated in the 1970s. Since then, the deployment of EGS projects has increased around the world [7–10]. The first pioneering EGS projects induced earthquakes with magnitude up to M<sub>L</sub>1.3 at the Fenton Hill project, United States [11,12], M<sub>L</sub>0.6 at the Hijiori project, Japan [13], and M<sub>L</sub>2.0 at the Rosemanowes project), which did not affect the continuation of the projects.

Fluid injection, operated at high pressure (i.e., in the order of tens of megapascals) during hydraulic stimulation of the low-permeability rock or at lower pressure during circulation phases, causes mechanical stress changes in the subsurface, which may lead to fracture/fault slip, causing permeability enhancement due to dilatancy and the triggering of earthquakes along the slipping pre-existing faults in the upper crust [14, 15]. Fluid-injection induced seismicity was observed for the first time at Rangely, Colorado (United States), where several tests of water injection were performed between 1969 and 1974, showing a marked correlation of the injected flow rate with the recorded seismicity [16,17]. Seismic activities have been documented in a number of geothermal projects worldwide [7,9,14,18–21]. This human-induced seismicity is classified as ‘triggered’ or ‘induced’, based on the location of the seismicity within the pressurized rock volume, and on the amount of stress perturbation due to engineering activities and the associated energy change ([22,23]; see also the discussion in [24,25]). However, for simplicity in this paper, the term ‘induced’ is used for all the earthquakes with anthropogenic origin, without distinction between ‘triggered’ and ‘induced’ seismicity.

Induced seismicity is a reasonably accepted consequence of hydraulic stimulations, even if it could be felt at the surface by the population, and is generally tolerated as long as its magnitude remains low, i.e., M<sub>w</sub> < 2 [8,9,26–29]. While the vast majority of these events consist of microearthquakes, instances of earthquakes with magnitude M<sub>w</sub> exceeding 3 have taken place, potentially causing perceptible ground shaking among the local population, damages, and the termination of a few projects [7–9,24]. Examples of those cases are the 2017 M<sub>w</sub>5.5 Pohang earthquake in South Korea [23], the 2006 M<sub>L</sub>3.4 Basel

earthquake in Switzerland [30], the 2021 M<sub>L</sub>3.9 Vendenheim earthquake in France [31,32] or the 2003 M<sub>w</sub>4.4 Berlín earthquake in El Salvador [33].

Earthquake magnitude of trailing seismicity is expected to differ to a certain degree of freedom from the magnitude of induced seismicity, expecting to decreasing through time following Bâth’s law [34,35]. However, some EGS projects experience larger-magnitude earthquakes after operations have ceased than during the operations. What is striking is the frequent occurrence of the largest magnitude earthquake (LME) after the cessation of injection in almost a quarter of the cases of EGS (Table 1, [21,36]), with delays from the shut-in varying between 1 h, as in Paralana EGS in Australia [37], to six months, like the circulation at the Vendenheim EGS in France [32]. This intriguing phenomenon is counterintuitive because stopping injection decreases pore pressure, which is expected to lower the magnitude and frequency of induced events. Late post-injection seismicity is particularly counterintuitive and appears difficult to control, posing challenges to the viability and safety of EGS deployments.

To mitigate such undesirable LME, research in the last two decades has put a special effort in improving the understanding of the mechanisms that ultimately cause these induced earthquakes, and drive their migration within the fault networks. Traditionally, fluid pressure variation resulting from injection has been considered the main cause of induced seismicity [17,47,48]. This traditional conceptualization cannot fully explain the occurrence of the LME after the cessation of injection. As pressure rapidly drops in the reservoir and migrates after shut-in, induced seismicity would be expected to diminish both in frequency and magnitude. In line with the traditional conceptualization of induced seismicity and considering that pressure changes are proportional to the injected fluid volume, relationships correlating the maximum seismic magnitude with the cumulative injected volume have been suggested [49,50]. Although this relationship between injected volume and maximum seismic magnitude is found to be valid for most cases of induced seismicity, including but not limited to EGS, some observed cases significantly deviate from this scaling, in particular for cases of post-injection seismicity in EGS. This is probably due to the

<caption>**Table 1**</caption>

EGS cases for which the post-injection induced earthquakes have higher magnitude (M<sub>w</sub>, M<sub>L</sub> in certain cases annotated with *) than during the injection phase, sorted as a function of the delay between shut-in and the time of the maximum magnitude earthquake. Note that the largest magnitude earthquake is not always felt on surface (M<sub>w</sub> < 2). SS: strike-slip; NF: normal faulting.

<table><thead><tr><th>Year</th><th>EGS project</th><th>Injection type</th><th>Injected volume (m³)</th><th>Depth (m)</th><th>Rheology</th><th>Stress Regime</th><th>M during injection</th><th>M post-injection</th><th>Timing of LME after shut-in</th><th>Distance LME-well</th><th>References</th></tr></thead><tbody><tr><td>2009</td><td>Landau</td><td>circulation - 1.9 year</td><td>balanced</td><td>3000</td><td>granite/ sediments</td><td>SS/NF</td><td>1.9*</td><td>2.7*</td><td>2 h</td><td>1.5–2 km</td><td>[8,38]</td></tr><tr><td>2011</td><td>Paralana</td><td>multi-stimulation (acid)</td><td></td><td>3960</td><td>quartzite</td><td>SS</td><td>0.85</td><td>1.45</td><td>1 h</td><td>400m</td><td>[37]</td></tr><tr><td>2006</td><td>Basel</td><td>stimulation - 6 days</td><td>11 570</td><td>4630</td><td>granite</td><td>SS/NF</td><td>2.1</td><td>2.94</td><td>5 h</td><td>250m</td><td>[27,39]</td></tr><tr><td>2003</td><td>Habanero-1, Cooper Basin</td><td>restimulation - 9 days</td><td>20 000</td><td>4250</td><td>granite</td><td>SS</td><td>1.6</td><td>3.7</td><td>1 d</td><td>350m</td><td>[40,41]</td></tr><tr><td>1993</td><td>GPK1-GPK2 circulation, Soultz-sous-Forêts</td><td>circulation - 4 months</td><td>44 000</td><td>3600</td><td>granite</td><td>SS/NF</td><td>–</td><td>1.9</td><td>9 d</td><td>–</td><td>[42,43]</td></tr><tr><td>2000</td><td>GPK2 well, Soultz-sous-Forêts</td><td>stimulation - 7 days</td><td>23 000</td><td>4955</td><td>granite</td><td>SS/NF</td><td>2.5</td><td>2.6</td><td>7 d</td><td>500m</td><td>[42,43]</td></tr><tr><td>2003</td><td>GPK3 well, Soultz-sous-Forêts</td><td>stimulation - 11 days</td><td>40 000</td><td>5091</td><td>granite</td><td>SS/NF</td><td>2.5</td><td>2.9</td><td>2 d</td><td>500m</td><td>[42,43]</td></tr><tr><td>2004</td><td>GPK4 well, Soultz-sous-Forêts</td><td>stimulation - 3.5 + 4 days</td><td>21 800</td><td>4982</td><td>granite</td><td>SS/NF</td><td>2</td><td>2.3</td><td>1 d</td><td>300m</td><td>[42,43]</td></tr><tr><td>2021</td><td>Vendenheim</td><td>circulation - 3 months</td><td>85 126</td><td>~5000</td><td>granite</td><td>SS/NF</td><td>3.6*</td><td>3.9*</td><td>180 d</td><td>–</td><td>[31,32, 44]</td></tr><tr><td>2003</td><td>Berlin Field</td><td>production - 11 years (10 injection wells)</td><td>2 x 100 000</td><td>2240</td><td>volcanic rock</td><td>SS</td><td>1.7</td><td>3.6</td><td>14 d</td><td>2 km</td><td>[9]</td></tr><tr><td>2017</td><td>Pohang</td><td>production - 20 months</td><td>5663 + 7135</td><td>4340</td><td>granite</td><td>SS/NF</td><td>3.3</td><td>5.5</td><td>59 d</td><td>300m</td><td>[23,45, 46]</td></tr><tr><td>2011</td><td>Cooper Basin Jolokia-1</td><td>stimulation - 7 days</td><td>380</td><td>4160</td><td>granite</td><td>SS</td><td>1*</td><td>1.6*</td><td>127 d</td><td>–</td><td>[40,41]</td></tr></tbody></table>
simplifications assumed in McGarr's relationship, such as disregarding the role of hydraulic conductivity and assuming a uniform pressure variation in the pressurized region, as well as considering that earthquakes exclusively occur in the pressurized region and that the region is likely seismogenic.

However, as the literature of the last 20 years has shown, induced seismicity, and particularly the post-injection one, is controlled by many triggering mechanisms, such as thermal and chemical interactions between the rock and the fluids, poroelastic effects, slip-induced frictional weakening, as well as stress perturbation associated with both earthquake-earthquake interactions and aseismic slip migration [51–54]. A specific challenge is to understand the processes causing post-injection trailing seismicity to mitigate the seismicity and reduce the occurrence of high-magnitude earthquakes after the injection ends. Considerable efforts have been dedicated to understanding and forecasting the underlying physical mechanisms and their effects.

Here, we aim to provide a comprehensive overview of all aspects of post-injection induced seismicity in EGS. The review is organized as follows. In Section 2, we present the basic concepts of initiation of fault activation and earthquakes, the main physical processes that trigger induced seismicity, and the coupling between them. Next, in Section 3, we present EGS cases in which the LME has been observed after the stop of injection (Table 1). The lessons learned in each of these LME cases are discussed. We finally introduce the recent advances in terms of forecasting and mitigation of high-magnitude induced seismicity in Section 4. We lastly suggest perspectives for future research to improve forecasting and mitigation of induced seismicity.

## 2. Physical processes of injection-induced seismicity in Enhanced Geothermal Systems

Mechanically, the occurrence of induced seismicity is intricately linked to both the shear strength and frictional stability of faults, which in turn depends on the mineralogical composition of materials within the seismic slip zone [55,56]. Earthquakes occur when fault frictional resistance is overcome, releasing the elastic energy stored in the subsurface. In natural seismicity, the stress acting on faults progressively accumulates due to tectonic forces until it reaches a threshold associated with the fault resistance, leading to the triggering of an earthquake, with subsequent seismic slip propagation and arrest. In EGS, fault failure and consequent seismicity are triggered by subsurface stress changes caused by hydraulic operations, both fluid injection and withdrawal. These stress changes become especially large during hydraulic stimulation of EGS, which aims at generating new fractures and at reactivating pre-existing fractures and faults to enhance their permeability. As a result, natural and induced seismicity is a complex process that depends on the initial stress before failure, fault strength, the stress drop and the temporal variability of loading on the plane [57].

### 2.1. Factors influencing the reactivation of faults in EGS

Seismicity is the result of fast slip (cm/s to m/s) due to stress changes on a geological fault, which is a pre-existing discontinuity that represents a zone of weakness in a volume of crustal rock [58]. In crustal rock (0–15-km depth), the faulting process primarily occurs within the brittle regime, influenced by prevailing pressure and temperature conditions. From a hydraulic viewpoint, the behaviour of a fault as either a barrier or a conduit for fluids is contingent upon the presence of infill material (gouge) and the extent of damage zone in the surroundings of the fault core, which determines its intrinsic permeability [59]. Faults are surrounded by damaged rock materials that can also affect their permeability. Fault failure often depends on whether the fault is behaving as a conduit or as a barrier for fluid flow [60–63]. In the former case, fluid migration can promote the fast pressurization of critical or weak fault portion, while in the latter case, stress variations can be large, making them more prone to induce seismicity [60]. Fault failure induces shear

slip accompanied by dilation, causing a permanent increase in fault aperture and thus permeability, attributed to the shear-induced mismatch of previously mated wall asperities [64,65]. However, it is plausible that faults may undergo other changes (i.e., healing, sealing, etc.) during their lifetime [66].

Shear failure is a dominant mechanism in hydraulic stimulation of fractured rock [67] and concerns faults that reactivate when the friction resistance is overcome by the shear forces. The occurrence of induced seismicity is generally related to the presence of critically stressed faults, with the initial stress tensor close to shear failure before injection. Critically-stressed faults may reactivate with minimal stress changes, while stable faults necessitate substantial stress alterations for reactivation. Once a fault is activated, the stability of frictional sliding depends on the local elastic stiffness of the rocks that surround the fault, the fault frictional properties and the rate of the reduction of shear strength (i.e., the frictional weakening) compared to the rate of elastic unloading on the fault [68]. In the theory of earthquake nucleation [58, 69], the frictional strength evolution can be described as function of slip velocity and slip history with the rate-and-state friction law [69–72]. If the fault has rate-weakening properties and the reduction of shear strength is fast, an earthquake can occur once the slipping region reaches a critical size [73]. Conversely, if the fault has rate-strengthening properties, slip is stable and aseismic. The factors that affect the rate-and-state frictional parameters and consequently the fault rheological stiffness and frictional stability include the mineralogical compositions of gouges, contact area, fluid pressure and temperature [74]. According to the earthquake nucleation theory, an increase in fluid pressure will increase the critical size for unstable slip, thus promoting aseismic slip [73]. Recent experimental studies of fluid injection on fault gouges in the laboratory have shown that the increase in fluid pressure can promote a transition of the parameters from velocity-strengthening to velocity-neutral/weakening, or conversely, from velocity-weakening to velocity-strengthening depending on the nature of fault gouge materials [74,75]. These observations demonstrate that frictional instability is a complex mechanism, and a large spectrum of fault slip behaviour can occur during fluid pressurization.

Another mechanism of rock failure due to fluid injection is tensile failure, which occurs when the increase of pore fluid pressure reaches the sum of the least principal stress, $\sigma_3$, and the rock tensile strength, $T_0$, ($P = \sigma_3 + T_0$). Tensile failure manifests along planes perpendicular to the least principal stress $\sigma_3$ and can occur during hydraulic stimulation operations when pore pressure exceeds $\sigma_3$, leading to the formation of new fractures. However, in deep crystalline rock like those found in EGS, shear failure occurs for pressure smaller than $\sigma_3$, therefore the observed seismicity is mostly associated to shear failure rather than tensile failure. Additionally, fracture opening, as opposed to shear failure, typically induces lower levels of seismicity [58,76].

### 2.2. Triggering mechanisms of injection-induced seismicity in EGS

Multiple coupled processes are acknowledged to induce failure and potentially trigger seismicity in EGS [7,9,52,77]. The increase in pressure, consequent to fluid injection, is one of the dominant triggering mechanisms which induces deformation and poromechanical stress changes, with associated variations of rock and fault hydro-mechanical properties. Because the injection is non-isothermal, there is cooling around the injector, which propagates in the subsurface, mostly driven by fluid flow. Temperature changes affect fluid properties (density and viscosity) and geochemical reactions [78]. Moreover, thermal contraction and thermoelastic stress arise. These processes, in turn, affect the fluid flow and thus the pressure field, creating a thermo-hydro-mechanical coupling. Fault reactivation and fracture propagation create an increased level of coupling because the consequent permeability variation impacts the pressure distribution [52,79, 80]. Recently, field experiments and large-scale observations have also shown that injection-induced aseismic slip plays an important role in the
triggering of earthquakes [75,81–84]. This subsection describes these mechanisms individually (Fig. 1), and is concluded by an explanation of their coupling and combined effects both during and after injection in EGS.

### 2.2.1. Pressure-driven mechanisms and associated poroelastic stressing

Fluid injection causes an increase in pore pressure at the injection well that diffuses into the rock. This pressure build-up is proportional to the injected fluid volume and inversely proportional to the hydraulic diffusivity of the reservoir, i.e., the ratio between the rock transmissivity and storativity. This pressure build-up propagates into the reservoir following a diffusive process, i.e., the pressure front $L(t)$ propagates in time as $L(t) = \sqrt{D_h}t$ [85]. Pore pressure increase causes the reduction of the effective normal stress and consequently of the shear resistance acting on a fault plane, which can reactivate the fault [17]. The pressure front continues to propagate even after the stop of injection and can destabilize distant faults for a long period after the injection cessation [86–90]. The post-injection triggering effects of pore pressure diffusion were recently outlined as a possible explanation of the trailing micro-seismicity observed after shut-in at the geothermal field of Coso, USA [91]. In fractured rock, fluids diffuse through preferential flow paths, i. e., faults and fractures, and progressively increase their pore pressure [92]. Critically-stressed faults have generally a higher permeability than other faults, and their periodic slip opens them up due to dilatancy and, thus, they become preferential flow-path for the injected fluid [93–95]. Consequently, fluid injection enhances the permeability of the most hydraulically-conductive faults [96,97].

Apart from these direct effects of pressure on the effective stresses acting on fault planes, fluid injection also induces poroelastic strain and

stress variation in the rock [98]. Because the effective stresses change inside the pressurized rock volume, there is a differential deformation between the pressurized and the non-pressurized zones which may cause destabilization ahead of the pressurized area and can trigger seismicity on faults at larger distance from the injection well, sometimes greater than 10 km [99–102]. This effect is amplified by the presence of faults and fractures, which additionally cause stress changes along them, leading to anisotropic poroelastic stress variations [88,103–105]. As a consequence, poroelasticity has the potential to improve or worsen the stability of faults depending on their orientation [90,106,107]. After the stop of injection, the pore pressure gradients rapidly attenuate and, thus, the forces inducing poroelastic stresses reduce, leading towards the homogenization of the stress tensor of the rock inside and outside the pressurized volume, diminishing the effects of poroelasticity [103]. This poroelastic stress relaxation, short-lasting after the stop of injection, can be sufficient to reactivate faults that had been stabilized during injection [90,108].

### 2.2.2. Thermal effects

In EGS, the fluid is generally injected at ambient temperature (~20 °C) into a rock at a temperature between 120 and 180 °C (at ~4-5-km depth). This thermal disparity spreads into the reservoir following heat transport processes. Given the low permeability of crystalline rock, heat transport is controlled by the coupling of thermal advection of the fluid through the fractures with the thermal conduction in the rock and the heat transfer between the fluid and the rock [109,110]. Cooling induces thermal rock contraction. The differential elastic strain in the cooled volume generates thermal stress reduction, similarly to the poroelastic process [111–113]. Thermoelasticity depends on the

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** The Mohr circle represents the stress tensor, with every point corresponding to a different orientation. The grey circle illustrates the initial stress state. The red dot indicates the fault plane orientations that fail corresponding to the points where the Mohr circle touches the failure envelope. (a) Pressure-driven mechanisms modify the stress tensor: the blue circle corresponds to the shift of the grey circle in response to an increase of pore pressure $\Delta p$, while the green circle corresponds to the combination of pressure increase with variation of total stress due to poroelasticity. (b) Thermoelasticity induces the shift of the initial circle to the left or to the right, and it can also induce variation of the circle size. (c) Geochemical interactions alter fault strength, i.e., cohesion and friction, which can facilitate reaching failure conditions; it may also alter the pressure propagation through the variation of porosity and permeability. (d) Static stress transfer from adjacent faults lead to decrease or increase of the circle, which can stabilize or destabilize the faults.</figcaption></figure>
temperature drop and the coefficient of thermal expansion of the rock, on the rock stiffness and on the tectonic structures in the subsurface. Although thermoelastic effects can be marked in stiff crystalline rock undergoing large temperature variation, they remain limited to the vicinity of the well during the duration of EGS hydraulic stimulation, affecting a much smaller area than the pressurized area [18]. Indeed, the thermal front propagates in the order of ~$10^{-3}\sqrt{t}$ m (t in second) for typical values of granitic rock and continuous injection, while pore pressure propagates in the order of ~$10^{-2} - 10^{-1}\sqrt{t}$ m, considering typical stiffness values of granite and equivalent permeability in the order of $10^{-18} - 10^{-16}$ m² [65,114]. However, long-term fluid circulation affects wider volume and thermal effects can become a major triggering mechanism of induced seismicity, even for distant faults [115]. At The Geysers geothermal plant (USA), where fluid circulation and heat production have been active for over 50 years, reservoir cooling and associated thermal-elastic shrinkage of the rock are believed to be the dominant mechanism of the largest injection-induced seismic events through cooling-induced shear slip [116].

### 2.2.3. Geochemical interactions

Fluid injection also disturbs the initial chemical equilibrium between the rock matrix and the resident fluid, promoting chemical interactions [78]. If the fluid has a lower/higher mineral content than the rock, mineral dissolution/precipitation is likely to occur [79]. These chemical interactions depend on the type of minerals, the pressure and the temperature of the fluids and the host rock [117]. Chemical interactions last for a long time, exceeding the geothermal operations, and can affect fault stability and potentially induce seismicity after the stop of injection. EGS reservoirs are commonly constituted of crystalline rock and cold-water injection favours dissolution of calcite in fluid paths. In certain cases, the dissolved species diffuse and precipitate, reducing the permeability farther away in the fracture [118-120]. Precipitation of amorphous silica is also common in granitic rock due to its faster precipitation compared to other minerals, such as quartz and feldspar [121-124]. Dissolution and precipitation may degrade rock stiffness and strength, as well as affecting fault asperities that weaken the fault friction capacity, emphasizing the potential of fault activation. Mineral dissolution increases porosity and permeability of both fractures and rocks. Variations in porosity and permeability, in turn, cause changes in pressure and temperature, and consequently stress variations in the stimulated rock.

### 2.2.4. Static stress transfer

Fault activation, triggered by any kind of mechanism, causes irreversible variations in the local stresses around the slipped area, which may promote additional seismicity [125-127]. This effect has been observed both in natural and induced earthquakes [128]. Static stress transfer causes stress redistribution that modifies the critical orientation of faults for failure by rotating the stress tensor [103]. The critical orientation depends on the initial stress state and on the ratio of the shear stress variation to the initial in-situ shear stress. When an earthquake is triggered, stress is redistributed over the sliding fault plane and adjacent faults in the network. The shear stress drop that occurs along the slipped area is proportional to the seismic magnitude, which is a function of the amount of slip and the rock stiffness, and inversely proportional to the slipping surface of the reactivated fault [129]. Generally, the stress drop ranges from 0.1 to 10 MPa [42,130]. To give an idea of the order of magnitude, the 1992 Landers natural earthquake (M<sub>w</sub> 7.4, USA) had a stress drop of 3.5 MPa, with aftershocks with a stress drop of 0.03 MPa [125]. At the Basel EGS project in Switzerland, the median value of the stress drop of the induced seismicity has been estimated at 2.3 MPa [131]. The similarity in the magnitude of stress drop between tectonic and induced earthquakes is still an open debate: the stress drop of induced events has been found to be comparable to natural earthquakes at the same depth in some cases [132-137], while

others present lower values of stress drop for induced earthquakes [138-147].

Fault slip induces antisymmetric variations of the stresses both in perpendicular and parallel directions to the fault (Fig. 2). Local stress redistribution promotes the failure of adjacent faults, while inhibiting the slip of certain faults as a function of their location and orientation [148-150]. Fault slip can induce earthquake initiation, initiating a dynamic earthquake-earthquake interaction promoting aftershock events on the same reactivated fault [129]. These earthquake-earthquake interactions have been studied in the 2011 Prague and 2016 Pawnee sequences in cases of wastewater disposals in Oklahoma, USA [52] and at the Weiyuan-Changning shale gas, China [151]. Even small seismic events influence fault stability and can become themselves a triggering mechanism of induced seismicity [128].

### 2.2.5. Stress perturbation caused by aseismic slip

Recently, fluid injection-induced aseismic fault slip has been highlighted as an active triggering mechanism of induced seismicity [75, 81-83,152-155]. During injection experiments at 282 m-depth, where confining pressures are lower than most of geo-energy applications, Guglielmi et al. [84] and Cappa et al. [75] have shown that fault aseismic slip and opening precede the fault slip acceleration that leads to seismicity. Thus, aseismic slip can migrate and potentially activate faults within and outside the pressurized region, redistributing stresses on asperities over the aseismically-slipping fault and on adjacent faults, promoting seismic activation (Fig. 3) [75,82,156,157]. Typically, faults featuring rough slip interfaces with asperities tend to primarily slip aseismically because fault friction governs the slip velocity [158]. The stress transfer caused by aseismic slip onto nearby faults is mechanically similar to the Coulomb static stress transfer discussed in Section 2.2.d. The amount of aseismic slip is influenced by the frictional properties of the fault and the criticality of initial fault stress to failure [156,159], as well as the total injected fluid volume [160,161]. It has been shown that aseismic slip over critically-stressed faults can trigger post-injection seismicity far away from the injection well [90,157,162-164], for a duration proportional to the duration of injection with a self-propagation along the activating fault without any further fluid pressure increase [165,166]. The potential timescale of the effects of aseismic slip is illustrated by the occurrence, 10 months after the cessation of completion of hydraulic fracturing, of the largest magnitude induced earthquake monitored in Canada, in a project of hydrocarbon storage in Western Canada in 2016 [167].

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Asymmetric static stress transfer due to dextral fault reactivation. Left-lateral static stress transfer is shown in blue and right-lateral stress transfer in red. The magnitude of stress redistribution depends on the surface of the fault, the amount of slip, the initial stress state and on mechanical properties of the rock. Dextral faults affected by right-lateral static stress transfer could be reactivated.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Fluid injection induces an aseismic creep propagation ahead of the pressurized front. (a) The stress perturbation due to creep can induce seismic activation on faults far from the injection well during the injection. (b) At the stop of injection, the aseismic creep is self-propagating without any further fluid pressure increase.</figcaption></figure>

A number of studies have pointed out that aseismic fault slip can precede seismic slip on a fault [75,84,168-171]. A fault with initial rate-strengthening properties (see Section 2.1.) could change to the velocity-weakening regime, capable of a seismic activation [172-174]. The observations of this process are quite novel and encourage new investigations to consider the possibility of mixed modes of friction slip in laboratory experiments and numerical models from fault failing first aseismically and then seismically. In addition, both aseismic and seismic slips degrade the frictional properties of the fault by deteriorating the fault asperities and reducing frictional resistance, promoting additional fault slip [51,175].

### 2.2.6. Coupled processes operating concurrently or consecutively both during co- and post-injection induced seismicity in EGS

Hydraulic stimulation aims to enhance the permeability of existing faults and fractures by increasing their aperture due to dilation during shear slip. To this end, a large volume of fluid is typically injected at high pressure, which modifies the stress conditions in the subsurface and initiates different physical mechanisms that are strictly interconnected [9,52].

During fluid injection (Fig. 4a), the pore pressure build-up in the host rock decreases the effective stresses acting within the rock matrix and on the faults. The pore pressure build-up is the principal mechanism responsible for the tensile opening and shear activation of faults in the vicinity of the injection well (Process 1, Fig. 4a). The differential elastic deformation between differently-pressurized rock volumes in the reservoir leads to variation of the total stress field, a phenomenon known as poroelasticity. As a consequence, fractures and faults located at the interfaces between non-pressurized and pressurized rock volumes may become destabilized. This poroelastic phenomenon may also have a marked effect in zones of the reservoir that are far from those affected by pore pressure build-up, because total stresses instantaneously propagate in the rock, especially in stiff low-permeability rock due to their initial undrained response (Process 2, Fig. 4a).

Thermal disparities between the injected fluid and the rock also induce variations of elastic stress, pressure (due to variations of fluid

density and viscosity) and volume deformation of the system. Thermal deformation affects the stability of the domain similarly to the poroelastic stressing (Process 3, Fig. 4a). Geochemical interactions between the rock and the fluid also modify the equilibrium of the domain and affect rock properties, such as porosity, permeability and stiffness (Process 4, Fig. 4a). In particular, geochemical reactions, i.e., dissolution and/or precipitation, may degrade the mechanical strength, which may bring a fault to failure conditions even if the stress state remains constant. Thermal and geochemical processes are strictly coupled with the fluid flow process and they are also dependent on each other. In fact, the transport of heat and chemicals is mostly driven by fluid advection in the system of connected fractures, and thermal- and chemical-induced porosity variation affect in turn the fluid flow and, thus, the pore pressure variation. Additionally, temperature variation can accelerate or delay geochemical reactions.

Moreover, static stress transfer due to fault activation (Process 5, Fig. 4a) causes a stress redistribution that may also trigger seismicity within and outside of the pressurized zone during injection. Aseismic creep propagates from the injection well into the host rock and can reactivate faults far away from the pressurized volume (Process 6, Fig. 4a). Slip activation causes compressive deformation in certain portions of the rock, which also increases pore pressure, potentially destabilizing nearby faults. This is in fact known as one of the mechanisms leading to the triggering of aftershocks (Process 7, Fig. 4a). In the case of long-term injections, the accumulation of pore pressure build-up and stresses acting on a pre-existing large structure can eventually trigger the activation of such structure, resulting in high-magnitude earthquakes (Process 8 in Fig. 4).

After the cessation of injection, seismicity is still observed for days to months in many EGS sites (Fig. 4b). Pore pressure build-up continues to diffuse into the reservoir for a long time after the stop of injection (Process 1, Fig. 4b). The post-injection normal closure of the fractures extends the pressurized front and amplifies the post-injection fluid propagation [176]. Fluids in pressurized dead-end fractures backflow at the stop of injection, but could also propagate the fractures, potentially inducing microseismicity or large-magnitude seismicity [177].
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Conceptual illustration explaining (a) co-injection and (b) post-injection triggering mechanisms of fluid-injection induced seismicity. Fluid is injected along a well and flows through fractures. (1) The increase of pore pressure opens fractures and enhances their permeability and consequently the circulation. (2). The deformation due to the pore pressure buildup in the vicinity of the well affects a wider area and produces poroelastic stress that can induce slip along distant faults. (3) Thermoelastic stressing affects the stability of faults in the vicinity of the well. (4) Chemical interactions affect the mechanical and hydraulic properties of faults. (5) The seismic, or aseismic, fault slips redistribute the stresses around the faults and can nucleate more seismicity and fault slips. (6) Aseismic creep diffuses from the injection well to the outside of the reservoir, even after the stop of injection. (7) Earthquake rupture induces others earthquakes on the same fault. (8) Stress accumulation on large faults due to distant and/or previous injections can induce high-magnitude seismic events.</figcaption></figure>

Poroelastic stress vanishes faster than pore pressure drop, which may lead to reactivations of faults that were stabilized during injection by poroelastic stress (Process 2, Fig. 4b). Aseismic creep continues to propagate along the domain after the injection is stopped and may

reactivate faults far from the injection well (Process 6, Fig. 4b). Thermal and geochemical interaction, static stress transfer, slip propagation and earthquake interaction (Processes 3, 4, 5, 6 and 7, Fig. 4b) are still acting after injection ends. Accumulation of pore pressure and stresses on
major faulting structures can also induce seismicity for a long time after the stop of the injection (Process 8, Fig. 4b). The pressure gradients, the injected volume, the pressurization rate, and the duration of injection play an important role in the destabilization of subsurface reservoirs because of the induced stress and pressure accumulation. The delay of post-injection induced seismicity depends on the hydro-mechanical properties of the rock and faults and also on the diffusivity of the reservoir.

## 2.3. From fault reactivation to induced seismic events

The size of the earthquake, i.e., the quantity of energy released with the seismic slip, depends on the amount and velocity of the slip, the size of the slipping area and the previously applied stresses on the fault plane [178]. Magnitude and frequency of seismic occurrence depend on multiple physical processes occurring at different scales, such as the fault frictional weakening or the fluid pressurization in the fault due to mechanical compression during frictional sliding, but also on tectonic structure geometries themselves [57,179,180].

To quantify the size of an earthquake, the Richter scale for local magnitude, $M_L$ [181], is widely used, but it can underestimate the magnitude of large earthquakes occurring at great depths. The current standard magnitude quantification is the moment magnitude, $M_w$ [182–184], which is not linked to the local magnitude, $M_L$, by a theoretical relation, although the ratio of $M_w/M_L$ is estimated to vary between 2/3 to 4/3 [185].

# 3. Identification of the potential mechanisms that triggered post-injection LME in EGS: summary of documented cases

EGS have been developed around the world for decades. However, the emergence of high-magnitude earthquakes and post-injection trailing seismicity is a hurdle to the positive perception on EGS projects by authorities and population, as cases like the Pohang EGS (South Korea, 2017) pointed out the risks associated to these projects [186]. In this section, we analyse the cases of post-injection LME to better understand the processes that control trailing seismicity. Interestingly, we can observe an increase in the magnitude of the post-injection LME as a function of the ratio between the delay of the LME and the duration of the injection (timepost-injection / timestimulation) (Fig. 5a). Note that pore pressure diffuses after the stop of injection a time similar to the injection one, so pressure diffusion becomes negligible for timepost-injection / timestimulation > 1. The cases are ordered by increasing ratio timepost-injection / timestimulation (Table 1, Fig. 5a). The magnitudes of the post-injection trailing largest earthquake are in the range of the LME monitored during operations of EGS projects (Table SI 1). Additional information on these cases and on cases of induced seismicity that occurred during the injection stage can be found in Table SI1 and in Majer et al. [9], Zang et al. [10], Foulger et al. [20], Buijze et al. [7], Kivi et al. [21] and De Simone et al. [114].

### 3.1. Landau, Germany

Landau is located in the Upper Rhine Graben, in the western part of Germany, 4 km away from the EGS project of Insheim (initiated in 2012). For both projects, their location in urban areas makes the induced seismicity a sensitive issue. The Landau EGS project was successfully and seismically-quiet; stimulated in 2007 through a doublet of wells separated by 1.3 km at approximately 3,000-m depth in a granitic reservoir [187]. After almost two years of production, the project was shut-in for maintenance in August 2009. One hour after the shut-in, a $M_L$ 2.7 event occurred 1.5–2 km north of the site, estimated at 2,300–3,300-m depth [8]. Seven more perceivable events were recorded after the LME. The location of the post-injection seismic events is not clear, as they could have nucleated either in the sediments, the basement, or both [38]. Due

<figure><img src="image_7.png" /><figcaption>Fig. 5. (a) Magnitude of the LME monitored during the fluid injection (empty circle) and the largest magnitude earthquake (LME) monitored after the stop of injection (full circle) as a function of the ratio between the delay of the post-injection LME of and the total duration of the stimulation (plot based on [36]). The study case of Jolokia-1 is an outlier (ratio equal to 18) and the case is not plotted to ease the reading of the figure. The grey vertical line at normalized delay of post-injection LME equal to 1 separates cases with early and late post-injection induced seismicity. SsF: Soultz-sous-Forêts. (b) Evolution of the effect of the different triggering mechanisms of post-injection induced seismicity as a function of the ratio timepost-injection / timestimulation.</figcaption></figure>

to the scarcity of information, the triggering mechanisms of post-injection LME have not been investigated in the published literature. The operations were resumed with a lower maximum injection pressure, reduced by 4.5 MPa, in November 2009.

### 3.2. Paralana, Australia

The Paralana EGS, South Australia, was initiated to provide power to local mining developments, but currently provides electricity at the national scale. The ground exploration started in 2007, and the Paralana-2 well was drilled in 2009 [37]. The reservoir was subject to multiple stimulations. The first large-scale hydraulic acid-stimulation was done in July 2011 at the depth of 3,960 m to enhance the permeability of the reservoir located between sedimentary and basement rocks, inducing microseismicity with a maximum magnitude of 0.85. Less than 1 h after the shut-in, a $M_w$ 1.45 earthquake occurred [37].

The inversion of permeability from injectivity and monitored seismicity shows that the pressurized volume, estimated numerically as a result of injecting 3,000 m³ of water, is smaller than the seismically active volume [188]. Moreover, the comparison of hydro-mechanical 3D models of fluid injection at the EGS site, accounting for poroelasticity or not, illustrates that poroelasticity is required to reproduce the events observed at a large distance from the injector at early times during the injection, which are far ahead of the pressurized front [189]. Riffault
et al. [189] show that, because of poroelastic effects, failure events concentrate in the direction of the maximum principal stress during injection, while they are inhibited along the minimum principal stress direction. After shut-in, the opposite occurs. However, this prediction of seismic event location does not correspond to the one observed in Paralana, probably due to the presence of rock heterogeneity, stress fluctuations and/or fracture presence that are neglected in the simplified model. Although Riffault et al. [189] were not able to fully capture the spatial distribution of seismic events in Paralana, they highlight the necessity to consider poroelastic stresses to explain co- and post-injection seismicity.

### 3.3. Basel, Switzerland

Basel EGS is located in the southern part of the Upper Rhine Graben in Switzerland, on the borders between France and Germany. After only 6 days of hydraulic stimulation of the granitic basement (11,570 m³ of water injected at 4,630-m depth) in December 2006, levels of observed seismicity higher than the traffic light system threshold (M > 2) led to the decision of stopping the injection [27]. 5 h later, the LME ($M_L$ 3.4) occurred at the edge of the pressurized area [39,190,191]. The well was bled-off to mitigate the triggering of more high-magnitude events, but levels of seismicity higher than 1 were recorded for months, including three events with magnitude close to the LME. After investigations and consequent to the strong public concern, the project was cancelled, remaining as a marked example to highlight the importance of controlling the post-injection trailing seismicity.

The Basel case attracted great interest of the scientific community and it has been analysed by means of different methods. For instance, Bachmann et al. [86] employed a hybrid methodology comparing a minimalistic model of pore pressure diffusion with the distribution of the monitored seismicity. The study shows that, during injection, the pore pressure increases and induces seismicity in the vicinity of the well, while it decreases at the stop of injection. Far from the well, pore pressure increases slightly after the shut-in, but not enough to trigger seismicity. The study suggests that static and dynamic stress changes from fault reactivation may have triggered the post-injection and farther induced seismicity. The Focal Mechanism Tomography (FMT) method [192,193], which consists of an inverse method based on the monitored seismicity to estimate the pore pressure required to nucleate each seismic event, also illustrates the limits of considering pore pressure as the unique trigger of post-injection induced seismicity. The method succeeds in explaining the co-injection and close-to-the-well earthquake initiation. However, post-injection LME located at 600 m from the injection well is estimated by the FMT method to nucleate with a required overpressure of 30 MPa, which is unrealistic because this value of overpressure coincides with the maximum injection pressure at the well (and overpressure logarithmically drops away from the well). The analytical study of the stress redistribution from monitored earthquakes coupled with pore pressure diffusion by Catalli et al. [148,194] highlights the predominance of the effects of pore pressure on the initiation of co-injection induced seismicity, and more importantly, the predominance of static stress transfer on the triggering of the post-injection trailing seismicity. Mukuhira et al. [195] proposed that the post-injection LME was triggered by the shear slip of a large fault plane after the post-injection homogenization of the pressure gradient along a large fault. This conjecture is based on interpretations of the monitored seismicity, and the evaluation of the pressure required to trigger failure according to the Mohr-Coulomb criterion, compared to the pressure variation induced by the injection. Going beyond the pressure diffusion process, a thermo-hydro-mechanical model proposed by Andrés et al. [196] studies the effects of the injection on a discrete fault taking into account poroelastic and thermoelastic effects. However, this study is limited to the co-injection period while the post-injection seismicity triggering is not analysed. Nonetheless, De Simone et al. [107] found that for the duration and injected volume of the stimulation at Basel, cooling

did not propagate enough to induce significant contraction and thermal stress reduction that could destabilize faults. In addition, Boyet et al. [108] presented a numerical hydro-mechanical model based on a simplified faulting network geometry inferred from seismic observations and showed that the combination of poroelastic stress relaxation at the moment of the shut-in and static stress transfer could explain the early post-injection LME at Basel (see Fig. 6). The case has been intensely studied and fostered the development of new methodologies to study induced seismicity and the analysis of triggering mechanisms other than pore pressure increase, leading to a number of different and often divergent explanations of the triggering mechanisms. Although there is not an established consensus on what mechanisms triggered the seismicity at Basel EGS, the most accepted hypothesis is that the post-injection LME was triggered by a combination of pore pressure diffusion, stress transfer and poroelastic stress relaxation after the injection ended.

### 3.4. Habanero-1 well, Cooper Basin, Australia

The EGS project in the Cooper Basin, South Australia, was developed from 2000 to 2015 [197]. The project produced electricity for the mining industry of the Cooper Basin, and was thus subject to little or no community concern for the risk of induced seismicity, accepting $M_w$ > 3 earthquakes during injection. The main stimulation of the Big Lake Suite granitic basement was initiated on November 30th 2003 on the Habanero-1 well, at 4,254-m depth at 280 °C [198–200]. The stimulation lasted 9 days, injecting 20,000 m³ of water, with a maximum pumping rate of 48 l/s [9]. One day after the injection cessation, the LME of $M_w$ 3.7 occurred. Most of the post-injection seismicity occurred on the outer-edge of the seismic cloud [201].

Because no clear breakdown in the Habanero-1 wellhead pressure could be noticed at the occurrence of the LME, it was assumed that the post-injection seismicity was mainly induced by repeated slips on subhorizontal fault asperities due to pressure-driven stress changes during injection [201,40]. It is also suggested that the seismicity was influenced by the different hydraulic stimulations from the multiple injection and production wells of the area [201]. A more recent study [202] analyses the potential effects of pore pressure diffusion and of aseismic slip of a main fault (modelled with velocity-strengthening) and seismic slip on secondary faults (modelled with velocity-weakening) due to fluid injection applied on another well, the Habanero-4, lasting 17 days in 2012. They estimate a large impact of aseismic slip on the total seismic release for this injection; which could be extended to previous well stimulations on the Habanero fault. Yet, no particular finding is made in this study about the post-injection triggering mechanisms at the Habanero-1, and for the stimulation of the Jolokia-1 well, also located in the Cooper Basin (Section 3.9.).

### 3.5. Soultz-sous-Forêts, France

The EGS project of Soultz-Sous-Forêts hosted the first successful circulation test between injection and production wells, and contributed to the improvement of the knowledge on the mitigation of induced seismicity along nine consecutive circulation tests [203–205]. The project is located in the French part of the Upper Rhine Graben. The geothermal granitic reservoir lays between 3,500 and 5,000-m depth and was stimulated by multiple injections in multiple wells [43].

The first circulation test was carried out in 1997 through the wells GPK1 and GPK2 during four months, in which 44,000 m³ of water were injected. A $M_w$ 1.9 earthquake occurred 9 days after the shut-in of the circulation test [9,43]. There is no published literature hypothesizing the mechanisms that triggered this post-injection earthquake induced by the circulation between GPK1 and GPK2 wells.

The second injection well GPK2 was deepened in 2000 (4,431–5,084-m depth) and stimulated through a progressive injection of 23,000 m³ of water during 7 days (injection designed in steps with flow rate of 30, 40
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** (a) Catalog of the clustered main events occurring during injection and after its stop at Basel, as reported by Deichmann et al. [39]. (b) Mohr circles for the fault build from the Cluster 88 in the hydro-mechanical model of a fault network [77]. Dashed circles correspond to the co-injection stage, solid circles to the post-injection stage. The blue circles correspond to the effects of pore pressure buildup, the green to the poroelasticity and the orange to the static stress transfer. During injection, the fault is stabilized by poroelastic effects, but the shut-in induces poroelastic stress relaxation and the reactivation of the fault.</figcaption></figure>

and 50 l/s). The largest seismic event during the injection had a magnitude of $M_w$ 2.5. 7 days after the shut-in, a $M_w$ 2.6 earthquake occurred [9,43]. In 2003, the stimulation of the GPK3 well induced post-injection seismicity, with a magnitude $M_w$ 2.9 occurring 2 days after its stop. During 11 days, 40,000 m³ of water were injected with an injection rate between 20 and 80 l/s. The injection design was then adapted with the shut-in by progressively decreasing the injection in stages after the previous injection high-magnitude earthquakes [206]. The following year, an earthquake of magnitude $M_w$ 2.3 occurred 1 day after the shut-in of the stimulation of the GPK4 well. The stimulation was performed in two phases, 9,300 m³ of water injection in 3.5 days and then 12,300 m³ in 4 days.

Interpretation of induced seismicity of the stimulation at the GPK2 well images its occurrence along large tectonic features destabilized by fluid injection [42,43]. Identification of seismic multiplets located on previously identified faults illustrates the repetitive ruptures of faults, whose density is high in Soultz-Sous-Forêts [152]. Because of the distance of the induced seismic events from the injection well, pore pressure is determined to have a minor role on the triggering of induced seismicity in the reservoir, but is effective for the propagation of aseismic creep along fault zones [168]. After the injection ended, the overpressure front diffused along large critically-oriented faults that require small stress variations to be activated [152]. Pressure diffusion and fault slips were confirmed as triggering mechanisms by a simple hydro-mechanical model reproducing the induced seismicity occurring on a subvertical fault zone crossing the injection well during and after an injection reproducing the GPK2 stimulation [207]. Calculations of the co-seismic stress changes resulting from monitored seismic events, i.e., the static stress transfer, enrich the identification of the mechanisms triggering post-injection induced earthquakes on the fault slipping patches, where pore pressure diffusion after shut-in alone would not be sufficient to induce fault slip after the injection stopped [149]. The presence of unstable fractures induced seismicity shortly after the stop of injection and the decay of trailing seismicity was controlled by the strength of the fault, following the Omori law [208]. Meanwhile, late post-injection induced seismicity in Soultz-Sous-Forêts is assumed to be due to post-injection pore pressure diffusion along the pre-existing fractures, inducing static stress transfer that propagated ahead of the overpressure front. Additionally, aseismic slip has been identified to contribute to induced seismicity during the fluid injection at the EGS site, which could still propagate after the stop of injection [152,168,209,210].

The monitored seismic events (more than 400 with a magnitude

$M_w$ > 1, 30 with $M_w$ > 2) nucleating during the stimulation of the GPK3 well were assumed to occur along large structures, promoting or hindering fluid circulation [42]. The wells in the project are hydraulically connected [211], allowing a complex fluid circulation and complicating the identification of the triggering mechanisms of the induced seismicity. The triggering mechanisms of the early post-injection induced seismicity from the injections at GPK3 and GPK4 wells are not specifically detailed. Yet, aseismic slip is recognized as a major triggering mechanism of induced seismicity in the EGS project of Soultz-Sous-Forêts by multiple studies comparing monitored seismicity and borehole slip measurements with injection parameters [152,168,209,210] and could have an effect, coupled to pressure-driven mechanisms on early post-injection induced seismicity. Moreover, another study, comparing stimulations modelling injection effects on stable and unstable pre-existing fractures, showed that the presence of unstable fractures in the reservoir induced seismicity shortly after the shut-in of the stimulation of the well GPK2 due to the pressure-driven effects at the stop of injection and their presence can be extended to the seismicity of the stimulation of the wells GPK3 and GPK4 [208].

### 3.6. Vendenheim, France

Located 30 km away from the EGS of Soultz-sous-Forêts, in the French part of the Upper Rhine Graben, the Vendenheim project was initiated in 2018 [31,32,44,212]. Tests were carried out from February 2018 until November 2019, followed by fluid injection to develop the doublet between GT1 and GT2 wells. Circulation took place from October 2020 until the beginning of December 2020, during which 85, 126 m³ of water were injected, causing the occurrence of an earthquake with local magnitude $M_L$ 3.6, a value higher than the $M_L$ 2 threshold established in the adopted Traffic Light System. Afterwards, a progressive bleed-off was operated from mid-December to the beginning of January, during which a $M_L$ 3.3 earthquake was recorded after 3 weeks. The well was then shut-in, but 6 months later, in June 2021, the LME occurred with a magnitude of $M_L$ 3.9 at 5 km from the project. The late post-injection event is suggested to be triggered by poroelastic pressure changes and/or by aseismic slip of a large fault far from the reservoir and hydraulically connected to it [44]. Further studies are needed, and expected for the near future, to shed light on this recent case of post-injection LME [213].
## 3.7. TR8A well, Berlín, El Salvador

Berlín EGS is located on a flank of the Cerro Tecapa volcano, a very high-seismically active region for which the last eruption occurred in 1878. The project operated through 10 wells since 1992 [9]. It was the first project adopting a built-in warning system for monitoring, quantifying and controlling the risks associated with induced seismicity [33]. In September 2003, 14 days after the shut-in of the second phase of the stimulation at the TR8A well at 2,240-m depth (with a maximum magnitude of $M_w$1.7), a $M_w$4.4 earthquake occurred 2 km away from the well.

The co-injection induced seismicity was spatio-temporally correlated to the stimulations and its seismic cloud was contained within 500 m from the injection well. Additional injections, performed southern to the well TR8A during the stimulation, have been suspected to be responsible for the distant LME [33]. However, interpretations of the source parameters of the seismicity do not find evidence that the post-injection induced seismicity was due to the multiple and simultaneous injections [33,214].

## 3.8. Pohang, South Korea

Fluid injection at the Pohang EGS was initiated in 2015 and it was the first attempt of a cyclic injection strategy [215]. The project performed 5 hydraulic stimulations for 20 months carried out at wells PX1 and PX2 at 4,340-m depth, within the basement. Two months after the stop of the 5th stimulation, an earthquake of magnitude $M_w$5.5 occurred in November 2017, causing severe damages in the surrounding urban areas [23,216,45]. This induced earthquake, the highest magnitude recorded in the post-injection stage in an EGS, led to the cancellation of the project and posed critical questions about the safety of EGS projects.

The expected magnitude estimated by the magnitude-injected volume scaling relationships [50,217] is significantly lower than the LME of magnitude $M_w$5.5 that was registered at Pohang; the required injection volume would be three orders of magnitude larger than what was injected. Sensitivity tests, performed by Chang et al. [218], comparing coupled and uncoupled hydro-mechanical models, highlight the importance of poroelasticity and static stress transfer to quantify their effects on the post-injection seismicity of the EGS project of Pohang. By combining a hydro-mechanical model of pore pressure diffusion and a Coulomb stress transfer model due to the slip of the large fault constituting the hydro-mechanical model, Yeo et al. [219] suggested that the co-injection seismicity was induced by pore pressure build-up, while the stress redistribution due to a large fault slip, associated with frictional weakening, triggered the post-injection LME initiation. Hydro-mechanical simulations considering a simplified representation of the Pohang case including two large faults (the largest located between the two wells) and assuming different values of fault permeability, show that in the case of higher permeability of the faults, fluid would have propagated faster with major Coulomb failure changes, and post-injection events would have occurred earlier [36]. Further models proposed by Yoo et al. [220], simulating the first two hydraulic stimulations in each well in a geometry including the major faults with a constitutive law including shear dilation and friction plastic strain-softening, also suggest that the large delay of the post-injection LME was likely due to a low permeability of faults, limiting the pore pressure diffusion between the two wells. The long-duration injection could have caused an accumulation of pore pressure and poroelastic stressing on a large and low-permeable fault on which the late post-injection LME occurred [218,219,221].

## 3.9. Jolokia-1 well, Cooper basin, Australia

After years of production in the Cooper Basin, a new stimulation was made through the Jolokia-1 well in October 2010, 10 km away of the Habanero-1 well location (see Section 3.4.). A total volume of

approximately 380 m³ was injected at 4,160-m depth during 7 days, with a maximum magnitude of induced events of $M_L$ 1.0. Several wells located in the area, 2 in the Jolokia area and 4 in the Habanero area, were simultaneously stimulated. Four months after the shut-in, a seismic event of magnitude $M_L$1.6 occurred [41].

Fault mechanisms interpreted from the focal mechanisms of the induced seismicity differ from the in-situ thrust-faulting regime, suggesting the creation of new fractures in the reservoir due to the large pressure changes [41]. Although the injected volume was relatively small, it induced seismicity in the vicinity of the well, where the over-pressure exceeded the least principal stress. However, this injected volume cannot explain the post-injection induced earthquake, which is suggested to be driven by stress variations associated to the many fluid injections in the region [41].

## 3.10. Predominance of mechanisms on early and late post-injection LME

Early post-injection seismicity occurs both after short-duration stimulations and circulation (in the case of Landau). In some cases, this post-injection seismicity is localized to the surrounding of the pressurized volume, and it can be attributed to pore pressure diffusion after the stop of injection. Yet, the effect of pore pressure build-up and diffusion cannot explain the triggering of the LME far from the injection well for cases of short-duration fluid injection and early seismicity occurrence, e.g., Basel and Paralana cases. Thus, poroelasticity is claimed as one of the main triggering mechanisms of the early post-injection seismicity in the EGS projects of Basel [108] and Paralana [188,189]. Slip-induced stress variations, both seismic and aseismic, are also considered as a triggering mechanism of the early post-injection induced seismicity. Indeed, slips of large faults due to pressure and poroelastic stress changes, and consequent static stress transfer, are suggested to trigger the co- and post-injection induced seismicity in the cases of Habanero-1 stimulation [201] and Basel [148,194,195]. Aseismic slip is also recognized as a triggering mechanism of co- and post-injection seismicity in the case of Soulitz-sous-Forêts [152,209].

Late post-injection induced seismicity occurs in cases of long-term stimulations, from either single or multiple wells. Pore pressure diffusion and stress accumulation from long-term injections on large faults are the main triggering mechanisms of induced seismicity in long-term stimulations. Indeed, significant volumes of water are injected and consequently are expected to potentially induce high-magnitude seismic events [50]. The delay between shut-in and post-injection LMEs is related to diffusion, which is controlled by rock permeability and stiffness [36,208]. Moreover, seismic and aseismic slips redistribute the stresses along faults of the domain and are also considered as triggering mechanisms of late post-injection induced seismicity for the cases of Pohang [219] and for the circulation in Vendenheim [44].

Pore pressure changes dissipate after a time equal to the time of injection. Therefore, poroelastic stresses will also become negligible after this time, so the stabilizing/destabilizing effect of poroelastic stress vanishing can only occur shortly after the stop of injection. Thus, early post-injection LME are mainly caused by pore pressure changes, poroelastic stress vanishment, and static stress transfer of seismic events (Fig. 5b). Late induced seismic events are caused mainly by aseismic stress transfer as aseismic slip accumulates in destabilized faults (Fig. 5b). Each study uses a different methodology and considers different coupled mechanisms, making the comparison between the cases difficult. The different mechanisms, i.e., poroelastic stress changes, static stress transfer, large fault seismic and aseismic slip, are effective in the triggering of post-injection LME, but with different importance depending on the specific characteristics of each site in terms of geology and tectonic structures.
# 4. Recent advances in the mitigation of induced seismicity

## 4.1. Understanding of the post-injection trailing seismicity

The studies mentioned above, focusing on specific EGS cases, as well as further studies considering general settings [88,97,106,128,155,173, 218], had greatly improved the understanding of the emergence of post-injection LME and the potential triggering mechanisms. The present review of the cases (Section 3), combining seismic interpretation and numerical analyses, shows that the delay of post-injection trailing seismicity is dependent on the diffusion of the injected fluid, the migration of aseismic slip, and the hydromechanical properties of the faults and the rock. In particular, early post-injection induced seismicity generally seems to be due to mechanisms that have immediate effects, such as poroelasticity, slip of nearby unstable faults and subsequent static stress transfer. Interestingly, late post-injection induced seismicity predominantly occurs in EGS projects where injection and/or circulation has taken place for a long time (months to years). Pore pressure diffusion, thermoelasticity and accumulation of stresses on large faults (induced by aseismic slip) due to multiple injections both in the same well or in multiple wells may cause LME late after the cessation of injection. Of course, large magnitude earthquakes during the stimulation and circulation stages (Table S1) are triggered by the same mechanisms, which are active since the initiation of fluid injection and extraction in the reservoirs.

The evidence that multiple triggering mechanisms play a role in post-injection seismicity challenges the traditional conceptualization in which induced seismicity is exclusively controlled by pore pressure changes (Fig. 5b). The triggering effects of poroelastic stressing have been shown to be paramount to understand and explain induced seismicity [90,107] and their consideration is becoming a norm in recent modelling studies. Apart from poroelastic stress, static stress transfer has also been found to play a relevant role in the reactivation of faults, both during injection and after the stop of injection. Recently, aseismic slip preceding the seismic slip during fault reactivation has been observed and the modelling of the propagating aseismic creep shows its significant impact on the post-injection trailing seismicity (Section 2.2.e.). Rock laboratory and field-scale experiments provide a unique opportunity to fill the knowledge gaps on fluid-induced seismicity in both space and time, such as the Åspö Hard Rock Laboratory in Sweden [222], the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) in Switzerland [223], the EGS Collab [224] and the Utah FORGE [225] in the USA, the Grimsel Test Site (GTS) in Switzerland [226,227], the Low Noise Underground Laboratory in France [75,84], the Tournemire in France [169,228], and the Mont Terri rock laboratory in Switzerland [61,229]. The review by Ji et al. [230] provides a complete and recent state-of-art on laboratory experiments of fault behaviour.

## 4.2. Real-time monitoring and mitigation of induced seismicity

Induced seismicity in EGS needs to be controlled both in frequency and magnitude. Monitoring systems are set to adjust injection parameters in response to the monitored seismicity. The Traffic Light System (TLS) is aimed to adapt the injection parameters (i.e., injection rate and pressure, and/or injected volume) in response to the monitored seismic magnitude and frequency occurrence. The thresholds and instructions depend on the area of the projects, for instance as a function of local communities and specific infrastructures [206,231,232]. The TLS was first applied in 1992 in the EGS project of Berlín, El Salvador (see Section 3.7.). The post-injection trailing seismicity is one of the most important factors to consider in TLS in order to maintain the safety of geo-energy applications [29,233]. Quantifying trailing seismicity is a challenge for the mitigation and the control of induced seismicity to ensure the safety of the different geo-energy applications.

A more advanced technique was recently adopted during the

stimulation of the St1-EGS project near Helsinki, Finland, in 2019, namely a near-real-time monitoring of the induced seismicity [234]. It consists of an automated system for a fast seismic interpretation but with low characterization of earthquake parameters; estimating for instance their location and magnitude and the evolution of the seismic and hydraulic energy. The development of this type of real-time monitoring TLS is promising for the future of EGS, especially for sites located in urban areas. Additionally, recent studies propose the development of new types of TLS, such as statistical, e.g., Adaptive Traffic Light Systems (ATLS) [235–238], or physics-based, e.g., Goertz-Allmann & Wiemer [131], in which the parameters can be calibrated during the fluid injection, based on seismic monitoring and fast-computing models to improve the forecasting potential of the models.

## 4.3. Injection protocols to mitigate induced seismicity

Novel injection strategies have been proposed to favour permeability enhancement while controlling the occurrence of induced seismicity above an undesired magnitude. For instance, a cyclic soft injection was applied at the EGS project of Pohang, South Korea, in 2017 (see Section 3.8.) to control the co-injection induced seismicity and keep it below the $M_w2.0$ threshold [215]. This injection strategy consists in cycles of high-rate/low-rate injection of specific duration, typically in the order of minutes. It is based on the concept of fatigue hydraulic fracturing, in which pressure pulses weaken the rock resistance by inducing micro-cracks that anticipate large failures [239]. The cyclic injection in the Pohang EGS project controlled the co-injection induced seismicity but did not avoid the occurrence of the high-magnitude earthquake two months after the shut-in of the latest stimulation. Moreover, innovative unconventional hydraulic stimulations, such as horizontal drilling or multi-stage fracturing in time and space, have been proposed to limit fault reactivation and to increase the volume of stimulated rock, improving heat production [240,241]. These stimulations aim to avoid the stress shadow effect, i.e., the stress redistribution due to previous injection stages that restrains the propagation of nearby fractures, preventing permeability enhancement in the affected fractures [240,242].

Furthermore, the protocol that defines how to stop the injection is important in the mitigation of post-injection trailing seismicity [243, 244]. For example, an abrupt shut-in destabilizes faults more than a progressive decrease of injection pressure [243,245,246]. Injection strategies need to be adapted for each EGS project and need to be efficient in the control of the permeability enhancement [247]. The development of injection strategies favouring tensile fracture (opening normal to the fault plane), and avoiding or limiting shear failure, and the development of injections that maintain aseismic the deformation of the rock, are currently studied by modelling, laboratory and field experiments. Because induced seismicity is not solely inherent to EGS, but also to other geo-energy application, investigations carried out in the context of applications such as hydraulic fracturing, wastewater management and gas storage, need to be integrated in the understanding of the different triggering mechanisms.

Novel concepts of EGS are also being proposed. An interesting suggestion, called *caging*, is to design injection projects, including EGS, with pre-drilled boundary wells around the target-stimulated reservoir to contain the injected fluid diffusion during operations. The boundary wells, behaving as fluid sinks, would halt fluid diffusion and fracture propagation along the reservoir. This concept has been applied to laboratory experiments on fractures and field analogues [248,249]. A second novel concept of EGS is now being developed at the Fervo Cape project, by drilling multiple doublets of horizontal hydraulically-fractured wells at the target reservoir depth to increase the stimulated surface (increasing the power capacity by several times, compared to conventional EGS) and allowing the heat production to be alternate between the different wells to insure fluid heating and limit rock cooling. The Fervo Cape project is, to this day, at its first stages of fluid circulation, but its technical advancements on drilling performance
are already uplifting [250].

## 5. Future perspectives

The major challenge of EGS development is the mitigation of both magnitude and frequency of the induced seismicity. The first suggestion is to adapt the injection protocols in response to the induced seismicity. Several types of injection protocols should be investigated to analyse their efficiency. For instance, the case of the cyclic injection is currently discussed regarding its efficiency to mitigate seismicity while simultaneously enhancing the permeability of the geothermal reservoir. The protocols for stopping injection, and the instructions given by TLS, are also investigated to determine whether shut-in or bleed-off is the safest way to control post-injection induced seismicity.

Recent studies on observed and modelled fault behaviour have proposed new explanations for fault reactivation. The continuation of laboratory and field-scale rock mechanics experiments is necessary to achieve a more comprehensive understanding of the processes involved in the reactivation of faults in deep and hot rocks. The recent observation of mixed slip-behaviour (velocity-weakening/strengthening) is currently being investigated at the field-scale in the Bedretto Underground Laboratory for Geosciences and Geoenergies and in the Mont Terri Underground Rock Laboratory in Switzerland. Moreover, experiments over faults with heterogeneous hydro-mechanical properties, and unfavourably orientated faults, including thermal components in the experiments, would enlarge the current understanding of the behaviour of different faults in highly-monitored environments subject to fluid injection.

The review of the different cases of post-injection trailing seismicity encourages the use of fully-coupled thermo-hydro-mechanical-chemical (THMC) numerical models to study the different mechanisms. The lack of data, and especially the difficulty in using the data to efficiently characterize the reservoir, is a challenge for the understanding and modelling of induced seismicity. Also, many newly-developed forecasting models are still considering pore pressure build-up as the only triggering mechanism. This is partly due to the high computational cost of fully-coupled THMC simulations, although the development of High-Performance Computing advances the development of robust THMC models that include fault reactivation and laboratory-derived friction laws. Their association with existing statistical forecasting tools is a perspective for better adaptation of the injection strategy to each EGS project. The combination of hybrid methods with a real-time monitoring is likely the way forward to control induced seismicity in EGS projects.

Despite the difficulty to anticipate and control induced seismicity, several projects are still in production, such as the projects of Soultz-sous-Forêts (France), Landau and Insheim (Germany), and Berlín (El Salvador). Induced seismicity can hinder the widespread development of EGS, and managing the triggering of earthquakes both in time and magnitude is a cornerstone for its future deployment. In this sense, the future EGS project of Haute-Sorne, Switzerland, is currently under development and its success in permeability enhancement and seismicity management will be decisive for the public perception of EGS projects as an important low-carbon energetic resource to reach net-zero emissions.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

A.B. and V.V. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.

georest.eu) under Grant agreement No. 801809. S.D.S. and V.V. acknowledge support from the Spanish Ministry of Science, Innovation and Universities through project HydroPoreII (PID2022-137652NB-C44). IMEDEA is an accredited "Maria de Maeztu Excellence Unit" (Grant CEX2021-001198, funded by MICIU/AEI/10.13039/501100011033). S.D.S. acknowledges the support by MICIU/AEI/10.13039/501100011033 and by the "European Union Next Generation EU/PRTR" through the 'Ramón y Cajal' fellowship (reference RYC2021-032780-I). F.C. acknowledges the financial support by the Agence Nationale de la Recherche (ANR) through the INSeiS project under contract ANR-22-CE49-0018 (PI: L. De Barros, Université Côte d'Azur, France) and the Institut Universitaire de France (IUF). We would like to acknowledge the Editor and the two reviewers for providing feedback, which helped us to improve the quality of the manuscript.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.rser.2025.116055.

## Data availability

No data was used for the research described in the article.

## References

[1] Horne R, Genter A, McClure M, Ellsworth W, Norbeck J, Schill E. Enhanced geothermal systems for clean firm energy generation. Nature Reviews Clean Technology 2025;1(2):148–60. https://doi.org/10.1038/s44359-024-00019-9.

[2] IEA. Net zero by 2050 (IEA). https://www.iea.org/reports/net-zero-by-2050; 2021.

[3] Ricks W, Voller K, Galban G, Norbeck JH, Jenkins JD. The role of flexible geothermal power in decarbonized electricity systems. Nat Energy 2024. https://doi.org/10.1038/s41560-023-01437-y.

[4] Barbier E. Geothermal energy technology and current status: an overview. Renew Sustain Energy Rev 2002;6(1–2):3–65. https://doi.org/10.1016/S1364-0321(02)00002-3.

[5] Brown D, DuTeaux R, Kruger P, Swenson D, Yamaguchi T. Fluid circulation and heat extraction from engineered geothermal reservoirs. Geothermics 1999;28(4–5):553–72. https://doi.org/10.1016/S0375-6505(99)00028-0.

[6] Tester JW, Anderson BJ, Batchelor AS, Blackwell DD, DiPippo R, Drake EM, Garnish J, Livesay B, Moore MC, Nichols K, Petty S, Nafi Toksoz M, Veatch RW, Baria R, Augustine C, Murphy E, Negraru P, Richards M. Impact of enhanced geothermal systems on US energy supply in the twenty-first century. Philos Trans R Soc A Math Phys Eng Sci 2007;365(1853):1057–94. https://doi.org/10.1098/rsta.2006.1964.

[7] Buijze L, van Bijsterveldt L, Cremer H, Paap B, Veldkamp H, Wassig BBT, van Wees J-D, van Yperen GCN, ter Heege JH, Jaarsma B. Review of induced seismicity in geothermal systems worldwide and implications for geothermal systems in the Netherlands. Neth J Geosci 2019;98:e13. https://doi.org/10.1017/njg.2019.6.

[8] Evans KF, Zappone A, Kraft T, Deichmann N, Moia F. A survey of the induced seismic responses to fluid injection in geothermal and CO2 reservoirs in Europe. Geothermics 2012;41:30–54. https://doi.org/10.1016/j.geothermics.2011.08.002.

[9] Majer EL, Baria R, Stark M, Oates S, Bommer J, Smith B, Asanuma H. Induced seismicity associated with enhanced geothermal systems. Geothermics 2007;36(3):185–222. https://doi.org/10.1016/j.geothermics.2007.03.003.

[10] Zang A, Oye V, Jousset P, Deichmann N, Gritto R, McGarr A, Majer E, Bruhn D. Analysis of induced seismicity in geothermal reservoirs – an overview. Geothermics 2014;52:6–21. https://doi.org/10.1016/j.geothermics.2014.06.005.

[11] Aki K, Fehler M, Aamodt RL, Albright JN, Potter RM, Pearson CM, Tester JW. Interpretation of seismic data from hydraulic fracturing experiments at the fenton hill, New Mexico, hot dry rock geothermal site. J Geophys Res Solid Earth 1982; 87(B2):936–44. https://doi.org/10.1029/JB087iB02p00936.

[12] Norbeck JH, McClure MW, Horne RN. Field observations at the Fenton Hill enhanced geothermal system test site support mixed-mechanism stimulation. Geothermics 2018;74:135–49. https://doi.org/10.1016/j.geothermics.2018.03.003.

[13] Sasaki S. Characteristics of microseismic events induced during hydraulic fracturing experiments at the Hijiori hot dry rock geothermal energy site, Yamagata, Japan. Tectonophysics 1998;289(1–3):171–88. https://doi.org/10.1016/S0040-1951(97)00314-4.

[14] Ellsworth WL. Injection-Induced earthquakes. Science 2013;341(6142):1225942. https://doi.org/10.1126/science.1225942.

[15] Elsworth D, Spiers CJ, Niemeijer AR. Understanding induced seismicity. Science 2016;354(6318):1380–1. https://doi.org/10.1126/science.aal2584.
[16] Byrne H, Silva JA, Plesch A, Juanes R, Shaw JH. The groundbreaking experiment in earthquake control at Rangely, Colorado, revisited. Geophys Res Lett 2020;47 (11):e2020GL088257. https://doi.org/10.1029/2020GL088257.

[17] Raleigh CB, Healy JH, Bredehoeft JD. An experiment in earthquake control at Rangely, Colorado. Science 1976;191(4233):1230-7. https://doi.org/10.1126/ science.191.4233.1230.

[18] Ghassemi A. A review of some rock mechanics issues in geothermal Reservoir development. Geotech Geol Eng 2012;30(3):647-64. https://doi.org/10.1007/ s10706-012-9508-3.

[19] Keranen KM, Weingarten M. Induced seismicity. Annu Rev Earth Planet Sci 2018; 46(1):149-74. https://doi.org/10.1146/annurev-earth-082517-010054.

[20] Foulger GR, Wilson MP, Gluyas JG, Julian BR, Davies RJ. Global review of human-induced earthquakes. Earth Sci Rev 2018;178:438-514. https://doi.org/ 10.1016/j.earscirev.2017.07.008.

[21] Kivi IR, Boyet A, Wu H, Walter L, Hanson-Hedgecock S, Parisio F, Vilarrasa V. Global physics-based database of injection-induced seismicity. Earth Syst Sci Data 2023;15(7):3163-82. https://doi.org/10.5194/essd-15-3163-2023.

[22] Dahm T, Cesca S, Hainzl S, Braun T, Krüger F. Discrimination between induced, triggered, and natural earthquakes close to hydrocarbon reservoirs: a probabilistic approach based on the modeling of depletion-induced stress changes and seismological source parameters. J Geophys Res Solid Earth 2015;120(4): 2491-509. https://doi.org/10.1002/2014JB011778.

[23] Ellsworth WL, Giardini D, Townsend J, Ge S, Shimamoto T. Triggering of the Pohang, Korea, Earthquake (Mw 5.5) by Enhanced Geothermal System Regulation. Seismol Res Lett 2019. https://doi.org/10.1785/0220190102.

[24] Grigoli F, Cesca S, Priolo E, Rinaldi AP, Clinton JF, Stabile TA, Dost B, Fernandez MG, Wiemer S, Dahm T. Current challenges in monitoring, discrimination, and management of induced seismicity related to underground industrial activities: a European perspective: challenges in induced seismicity. Rev Geophys 2017;55(2):310-40. https://doi.org/10.1002/2016RG000542.

[25] McGarr A, Simpson D, Seeber L, Lee W. Case histories of induced and triggered seismicity. Int Geophys Res 2002;21:81-674-64.

[26] Bao X, Eaton DW. Fault activation by hydraulic fracturing in western Canada. Science 2016;354(6318):1406-9. https://doi.org/10.1126/science.aag2583.

[27] Häring MO, Schanz U, Ladner F, Dyer BC. Characterisation of the Basel 1 enhanced geothermal system. Geothermics 2008;37(5):469-95. https://doi.org/ 10.1016/j.geothermics.2008.06.002.

[28] Schultz R, Skoumal RJ, Brudzinski MR, Eaton D, Bapie T, Ellsworth W. Hydraulic fracturing-induced seismicity. Rev Geophys 2020;58(3). https://doi.org/ 10.1029/2019RG000695.

[29] Schultz R, Beroza GC, Ellsworth WL. A risk-based approach for managing hydraulic fracturing-induced seismicity. Science 2021;372(6541):504-7. https:// doi.org/10.1126/science.abg5451.

[30] Deichmann N, Giardini D. Earthquakes induced by the stimulation of an enhanced geothermal System below Basel (Switzerland). Seismol Res Lett 2009; 80(5):784-98. https://doi.org/10.1785/gssrl.80.5.784.

[31] Lengliné O, Schmittbuhl J, Drif K, Lambotte S, Grunberg M, Kinscher J, Sira C, Schlupp A, Schaming M, Jund H, Masson F. The largest induced earthquakes during the GEOVEN deep geothermal project, Strasbourg, 2018-2022: from source parameters to intensity maps. Geophys J Int 2023;234(3):2445-57. https://doi.org/10.1093/gji/ggad255.

[32] Schmittbuhl J, Lambotte S, Lengliné O, Grunberg M, Jund H, Vergne J, Cornet F, Doubre C, Masson F. Induced and triggered seismicity below the city of Strasbourg, France from November 2019 to January 2021. C R Geosci 2021;353 (S1):561-84. https://doi.org/10.5802/crgeos.71.

[33] Bommer JJ, Oates S, Cepeda JM, Lindholm C, Bird J, Torres R, Marroquín G, Rivas J. Control of hazard due to induced seismicity by a hot fractured rock geothermal project. Eng Geol 2006;83(4):287-306. https://doi.org/10.1016/j. enggeo.2005.11.002.

[34] Schultz R, Ellsworth WL, Beroza GC. Statistical bounds on how induced seismicity stops. Sci Rep 2022;12(1):1184. https://doi.org/10.1038/s41598-022-05216-9.

[35] Verdon JP, Bommer JJ. Green, yellow, red, or out of the blue? An assessment of Traffic Light Schemes to mitigate the impact of hydraulic fracturing-induced seismicity. J Seismol 2021;25(1):301-26. https://doi.org/10.1007/s10950-020- 09966-9.

[36] Kim K-I, Yoo H, Park S, Yim J, Xie L, Min K-B, Rutqvist J. Induced and triggered seismicity by immediate stress transfer and delayed fluid migration in a fractured geothermal reservoir at Pohang, South Korea. Int J Rock Mech Min Sci 2022;153: 105098. https://doi.org/10.1016/j.jrmrms.2022.105098.

[37] Albaric J, Oye V, Langet N, Hasting M, Lecomte I, Iranpour K, Messeiller M, Reid P. Monitoring of induced seismicity during the first geothermal reservoir stimulation at Paralana, Australia. Geothermics 2014;52:120-31. https://doi. org/10.1016/j.geothermics.2013.10.013.

[38] Groos J, Zeiß J, Grund M, Ritter J. Microseismicity at two geothermal power plants at Landau and Insheim in the Upper Rhine Graben, Germany. EGU2013-2742. EGU General Assembly Conference Abstracts; 2013.

[39] Deichmann N, Kraft T, Evans KF. Identification of faults activated during the stimulation of the basal geothermal project from cluster analysis and focal mechanisms of the larger magnitude events. Geothermics 2014;52:84-97. https://doi.org/10.1016/j.geothermics.2014.04.001.

[40] Asanuma H, Nozaki H, Niitsuma H, Wyborn D. Interpretation of micro seismic events with larger magnitude collected at Cooper Basin, Australia. GRC Trans 2005;29:87-91.

[41] Baisch S, Rothert E, Stang H, Vörös R, Koch C, McMahon A. Continued geothermal reservoir stimulation experiments in the cooper Basin (Australia).

Beull Seismol Soc Am 2015;105(1):198-209. https://doi.org/10.1785/ 0120140208.

[42] Charléty J, Cuenot N, Dorbath L, Dorbath C, Haessler H, Frogneux M. Large earthquakes during hydraulic stimulations at the geothermal site of soulitz-sous- forêts. Int J Rock Mech Min Sci 2007;44(8):1091-105. https://doi.org/10.1016/j. ijrmmms.2007.06.003.

[43] Dorbath L, Cuenot N, Genter A, Frogneux M. Seismic response of the fractured and faulted granite of soulitz-sous-forets (France) to 5 km deep massive water injections. Geophys J Int 2009;177(2):653-75. https://doi.org/10.1111/j.1365- 246X.2009.04030.x.

[44] Fiori R, Vergne J, Schmittbuhl J, Zigone D. Monitoring induced microseismicity in an urban context using very small seismic arrays: the case study of the Vendenheim EGS project. GEOPHYSICS 2023;88(5):WB71-87. https://doi.org/ 10.1190/geo2022-0620.1.

[45] Kim K-H, Ree J-H, Kim Y, Kim S, Kang SY, Seo W. Assessing whether the 2017 M<sub>w</sub> 5.4 Pohang earthquake in South Korea was an induced event. Science 2018;360 (6392):1007-9. https://doi.org/10.1126/science.aat6081.

[46] Korean Government Commission. Summary report of the Korean government commission on relations between the 2017 pohang earthquake and EGS project. Geological Society of Korea 2019.

[47] Healy JH, Rubey WW, Griggs DT, Raleigh CB. The Denver earthquakes. Science 1968;161(3848):1301-10. https://doi.org/10.1126/science.161.3848.1301.

[48] Hubbert KM, Rubey WW. Role of fluid pressure in mechanics of overthrust faulting. Geol Soc Am Bull 1959;70(2):115-66. https://doi.org/10.1130/0016- 7606(1959)70[115:ROFPIM]2.0.CO;2.

[49] McGarr A. Seismic moments and volume changes. J Geophys Res 1976;81(8): 1487-94. https://doi.org/10.1029/JB081008p01487.

[50] McGarr A. Maximum magnitude earthquakes induced by fluid injection: limits on fluid injection earthquakes. J Geophys Res Solid Earth 2014;119(2):1008-19. https://doi.org/10.1002/2013JB010597.

[51] Eyre TS, Eaton DW, Garagash DI, Zecevic M, Venieri M, Weir R, Lawton DC. The role of aseismic slip in hydraulic fracturing-induced seismicity. Sci Adv 2019;5 (8):eav7172. https://doi.org/10.1126/sciadv.aav7172.

[52] Ge S, Saar MO. Review: induced seismicity during Geoenvironment Development-A hydromechanical perspective. J Geophys Res Solid Earth 2022;127(3). https:// doi.org/10.1029/2021JB023141.

[53] Kroll KA, Cochran ES. Stress controls rupture extent and maximum magnitude of induced earthquakes. Geophys Res Lett 2021;48(11):e2020GL092148. https:// doi.org/10.1029/2020GL092148.

[54] Moein MJA, Langenbruch C, Schultz R, Grigoli F, Ellsworth WL, Wang R, Rinaldi AP, Shapiro S. The physical mechanisms of induced earthquakes. Nat Rev Earth Environ 2023;4(12):847-63. https://doi.org/10.1038/s43017-023-00497-8.

[55] Collettini C, Nemeijer A, Viti C, Marone C. Fault zone fabric and fault weakness. Nature 2009;462(7275):907-10. https://doi.org/10.1038/nature08585.

[56] Scuderi MM, Collettini C, Marone C. Frictional stability and earthquake triggering during fluid passing stimulation of an experimental fault. Earth Planet Sci Lett 2017;477:84-96. https://doi.org/10.1016/j.epsl.2017.08.009.

[57] Kanamori H, Brodsky EE. The physics of earthquakes. Rep Prog Phys 2004;67(8): 1429-96. https://doi.org/10.1088/0034-4885/67/8/R03.

[58] Scholz CH. Earthquakes and faulting. Cambridge University Press: 2002.

[59] Caine JS, Evans JP, Forster CB. Fault zone architecture and permeability structure. Geology 1996;24(11):1025. https://doi.org/10.1130/0091-7613 (1996)024<1025:FZAAPS>2.3.CO;2.

[60] Wu H, Fu P, Frone Z, White MD, Ajo-Franklin JB, Morris JP, Knox HA, Schwering PC, Strickland CE, Roberts BQ, Vermeul VR, Mattson ED, Ingraham MD, Kneafsey TJ, Blankenship DA. Modeling heat transport processes in enhanced geothermal systems: a validation study from EGS Collab Experiment 1. Geothermics 2021;97:102254. https://doi.org/10.1016/j. geothermics.2021.102254.

[61] Cappa F, Guglielmi Y, Nussbaum C, De Barros L, Birkholzer J. Fluid migration in low-permeability faults driven by decoupling of fault slip and opening. Nat Geosci 2022;15(9):747-51. https://doi.org/10.1038/s41561-022-00993-4.

[62] Galloway E, Hauck T, Corlett H, Paná D, Schultz R. Faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing-induced seismicity. Proc Natl Acad Sci 2018;115(43). https://doi.org/10.1073/ pnas.1807549115.

[63] Vilarrasa V, Makhnenko R, Gheibi S. Geomechanical analysis of the influence of CO2 injection location on fault stability. Journal of Rock Mechanics and Geotechnical Engineering 2016;8(6):805-18. https://doi.org/10.1016/j. jrmge.2016.06.006.

[64] Barton N, Bandis S, Bakhtar K. Strength, deformation and conductivity coupling of rock joints. Int J Rock Mech Min Sci Geomech Abstracts 1985;22(3):121-40. https://doi.org/10.1016/0148-9062(85)93227-9.

[65] Jaeger JC, Cook NG, Zimmerman R. Fundamentals of rock mechanics. John Wiley & Sons; 2009.

[66] Li VC. Mechanics of shear rupture applied to earthquake zones. In: Fracture mechanics of rock. Elsevier; 1986.

[67] McClure M, Horne R. Characterizing hydraulic fracturing with a tendency-for- shear-stimulation test. SPE Reservoir Eval Eng 2014;17(2):233-43. https://doi. org/10.2118/166332-PA.

[68] Garagash DI, Germanovich LN. Nucleation and arrest of dynamic slip on a pressurized fault. J Geophys Res Solid Earth 2012;117(B10):2012JB009209. https://doi.org/10.1029/2012JB009209.

[69] Scholz CH. Earthquakes and friction laws. Nature 1998;391(6662):37-42. https://doi.org/10.1038/34097.
[70] Dieterich J. Time-dependent friction and the mechanics of stick-slip. Pure Appl Geophys 1978;116:790-806. https://doi.org/10.1007/BF00876539.

[71] Marone C. The effect of loading rate on static friction and the rate of fault healing during the earthquake cycle. Nature 1998;391(6662):69-72. https://doi.org/10.1038/34157.

[72] Ruina A. Slip instability and state variable friction laws. J Geophys Res Solid Earth 1983;88(B12):10359-70. https://doi.org/10.1029/JB088iB12p10359.

[73] Ohnaka M. A physical scaling relation between the size of an earthquake and its nucleation zone size. Pure Appl Geophys 2000;157(11):2259-82. https://doi.org/10.1007/PL00001084.

[74] Scuderi MM, Colletti C. The role of fluid pressure in induced vs. triggered seismicity: insights from rock deformation experiments on carbonates. Sci Rep 2016;6(1):24852. https://doi.org/10.1038/srep24852.

[75] Cappa F, Scuderi MM, Colletti C, Guglielmi Y, Avouac J-P. Stabilization of fault slip by fluid injection in the laboratory and in situ. Sci Adv 2019;5(3):eaaau4065. https://doi.org/10.1126/sciadv.aau4065.

[76] Clark JB. A hydraulic process for increasing the productivity of Wells. J Petrol Technol 1949;1(1):1-8. https://doi.org/10.2118/949001-G.

[77] Boyet A, De Simone S, Vilarrasa V. Physics-based modeling to understand and to propose forecasting methods of induced seismicity. Seismol Res Lett 2023;94: 2666-78. https://doi.org/10.1785/0220230109.

[78] Niemeijer A, Di Toro G, Griffith WA, Bistacchi A, Smith SAF, Nielsen S. Inerring earthquake physics and chemistry using an integrated field and laboratory approach. J Struct Geol 2012;39:2-36. https://doi.org/10.1016/j.jsg.2012.02.018.

[79] Pandey SN, Vishal V, Chaudhuri A. Geothermal reservoir modeling in a coupled thermo-hydro-mechanical-chemical approach: a review. Earth Sci Rev 2018;185: 1157-69. https://doi.org/10.1016/j.earscirev.2018.09.004.

[80] Zareidarmiyan A, Salarirad H, Vilarrasa V, Kim K-I, Lee J, Min K-B. Comparison of numerical codes for coupled thermo-hydro-mechanical simulations of fractured media. J Rock Mech Geotech Eng 2020;12(4):850-65. https://doi.org/10.1016/j.jrmge.2019.12.016.

[81] Cornet FH. The relationship between seismic and aseismic motions induced by forced fluid injections. Hydrogeol J 2012;20(8):1463-6. https://doi.org/10.1007/s10040-012-0901-z.

[82] Vilarrasa V, De Simone S, Carrera J, Villasenor A. Unraveling the causes of the seismicity induced by underground gas storage at Castor, Spain. Geophys Res Lett 2021;48(7). https://doi.org/10.1029/2020GL092038.

[83] Wei S, Avouac J-P, Hudnut KW, Donnellan A, Parker JW, Graves RW, Helmberger D, Fielding E, Liu Z, Cappa F, Eneva M. The 2012 brawley swarm triggered by injection-induced aseismic slip. Earth Planet Sci Lett 2015;422: 115-25. https://doi.org/10.1016/j.epsl.2015.03.054.

[84] Guglielmi Y, Cappa F, Avouac J-P, Henry P, Elsworth D. Seismicity triggered by fluid injection-induced aseismic slip. Science 2015;348(6240):1224-6. https://doi.org/10.1126/science.aab0476.

[85] Knudby C, Carrera J. On the use of apparent hydraulic diffusivity as an indicator of connectivity. J Hydrol 2006;329(3-4):377-89. https://doi.org/10.1016/j.jhydrol.2006.02.026.

[86] Bachmann CE, Wiemer S, Goertz-Allmann BP, Woessner J. Influence of pore-pressure on the event-size distribution of induced earthquakes: pore pressure and earthquake size distribution. Geophys Res Lett 2012;39(9). https://doi.org/10.1029/2012GL051480.

[87] Hsieh PA, Bredehoeft JD. A reservoir analysis of the Denver earthquakes: a case of induced seismicity. J Geophys Res Solid Earth 1981;86(B2):903-20. https://doi.org/10.1029/JB086iB02p00903.

[88] Kivi IR, Vilarrasa V, Kim K-I, Yoo H, Min K-B. On the role of poroelastic stressing and pore pressure diffusion in discrete fracture and fault system in triggering post-injection seismicity in enhanced geothermal systems. Int J Rock Mech Min Sci 2024;175:105673. https://doi.org/10.1016/j.ijrmms.2024.105673.

[89] Kivi IR, Vilarrasa V, Kim KI, Yoo H, Min KB. Bleed-off control on post-injection seismicity in enhanced geothermal systems. Undergr Space 2025;22:21-38. https://doi.org/10.1016/j.undsp.2024.08.009.

[90] Segall P, Lu S. Injection-induced seismicity: poroelastic and earthquake nucleation effects: injection induced seismicity. J Geophys Res Solid Earth 2015; 120(7):5082-103. https://doi.org/10.1002/2015JB012060.

[91] Holmgren JM, Kaven JO, Oye V. Long-term trends in microseismicity during operational shut-ins at the coso geothermal field, California. The Seismic Record 2025;5(1):73-82. https://doi.org/10.1785/0320240041.

[92] Zareidarmiyan A, Parisio F, Makhmenko RY, Salarirad H, Vilarrasa V. How equivalent are equivalent porous media? Geophys Res Lett 2021;48(9). https://doi.org/10.1029/2020GL089163.

[93] Barton CA, Zoback MD, Moos D. Fluid flow along potentially active faults in crystalline rock. Geology 1995;23(8):683. https://doi.org/10.1130/0091-7613 (1995)023<0683:FFAPAF>2.3.CO;2.

[94] Ito T, Zoback MD. Fracture permeability and in situ stress to 7 km depth in the KTB scientific drillhole. Geophys Res Lett 2000;27(7):1045-8. https://doi.org/10.1029/1999GL011068.

[95] Townend J, Zoback MD. How faulting keeps the crust strong. Geology 2000;28 (5):399. https://doi.org/10.1130/0091-7613(2000)28<399:HFKTC>S.2.0.CO;2.

[96] Langenbruch C, Weingarten M, Zoback MD. Physics-based forecasting of man-made earthquake hazards in Oklahoma and Kansas. Nat Commun 2018;9(1): 3946. https://doi.org/10.1038/s41467-018-01617-4.

[97] Zhang Y, Person M, Rupp J, Ellett K, Celia MA, Gable CW, Bowen B, Evans J, Bandilla K, Mozley P, Dewers T, Elliot T. Hydrogeologic Controls on Induced Seismicity in Crystalline Basement Rocks Due to Fluid Injection into Basal

Reservoirs: Y. Zhang et al. Ground Water xx, no. xx: xx-xx. Groundwater 2013;51 (4):525-38. https://doi.org/10.1111/gwat.12071.

[98] Wang H. Theory of linear poroelasticity with applications to geomechanics and hydrogeology. Princeton University Press; 2000.

[99] De Simone S, Carrera J. Analytical solutions to coupled HM problems to highlight the nonlocal nature of aquifer storage: nonlocal storage. Water Resour Res 2017; 53(11):9580-99. https://doi.org/10.1002/2017WR020824.

[100] Goebel THW, Weingarten M, Chen X, Haffener J, Brodsky EE. The 2016 Mw5.1 fairview, Oklahoma earthquakes: evidence for long-range poroelastic triggering at >40 km from fluid disposal Wells. Earth Planet Sci Lett 2017;472:50-61. https://doi.org/10.1016/j.epsl.2017.05.011.

[101] Goebel THW, Brodsky EE. The spatial footprint of injection wells in a global compilation of induced earthquake sequences. Science 2018;361(6405):899-904. https://doi.org/10.1126/science.aat5449.

[102] Segall P, Fitzgerald SD. A note on induced stress changes in hydrocarbon and geothermal reservoirs. Tectonophysics 1998;289(1-3):117-28. https://doi.org/10.1016/S0040-1951(97)00311-9.

[103] De Simone S, Carrera J, Vilarrasa V. Superposition approach to understand triggering mechanisms of post-injection induced seismicity. Geothermics 2017; 70:85-97. https://doi.org/10.1016/j.geothermics.2017.05.011.

[104] Segall P. Earthquakes triggered by fluid extraction. Geology 1989;17(10):942. https://doi.org/10.1130/0091-7613(1989)017<0942:ETBFE>2.3.CO;2.

[105] Zareidarmiyan A, Salarirad H, Vilarrasa V, De Simone S, Olivella S. Geomechanical response of fractured reservoirs. Fluids 2018;3(4):70. https://doi.org/10.3390/fluids3040070.

[106] Chang KW, Segall P. Injection-induced seismicity on basement faults including poroelastic stressing: induced seismicity on basement faults. J Geophys Res Solid Earth 2016;121(4):2708-26. https://doi.org/10.1002/2015JB012561.

[107] De Simone S, Vilarrasa V, Carrera J, Alcolea A, Meier P. Thermal coupling may control mechanical stability of geothermal reservoirs during cold water injection. Phys Chem Earth, Parts A/B/C 2013;64:117-26. https://doi.org/10.1016/j.pce.2013.01.001.

[108] Boyet A, De Simone S, Vilarrasa V, Ge S. Poroelastic stress relaxation, slip stress transfer and friction weakening controlled post-injection seismicity at the basal enhanced geothermal system. Commun Earth Environ 2023. https://doi.org/10.1038/s43247-023-00764-y.

[109] Bödvässon GS, Tsang CF. Injection and thermal breakthrough in fractured geothermal reservoirs. J Geophys Res Solid Earth 1982;87(B2):1031-48. https://doi.org/10.1029/JB087iB02p01031.

[110] Gringarten AC, Witherspoon PA, Ohnishi Y. Theory of heat extraction from fractured hot dry rock. J Geophys Res 1975;80(8):1120-4. https://doi.org/10.1029/JB080i008p01120.

[111] Biot MA. Thermoelasticity and irreversible thermodynamics. J Appl Phys 1956;27 (3):240-53. https://doi.org/10.1063/1.1722351.

[112] Palciauskas VV, Domenico PA. Characterization of drained and undrained response of thermally loaded repository rocks. Water Resour Res 1982;18(2): 281-90. https://doi.org/10.1029/WR018i002p00281.

[113] Zimmerman RW. Coupling in poroelasticity and thermoelasticity. Int J Rock Mech Min Sci 2000;37(1-2):79-87. https://doi.org/10.1016/S1365-1609(99)00094-5.

[114] De Simone S, Kivi IR, Min K-B, Rutqvist J. Chapter 9: induced seismicity in EGS: observations and triggering mechanisms. In: Enhanced geothermal systems (EGS). first ed. CRC Press; 2023. p. 39.

[115] Kivi IR, Pujades E, Rutqvist J, Vilarrasa V. Cooling-induced reactivation of distant faults during long-term geothermal energy production in hot sedimentary aquifers. Sci Rep 2022;12(1):2065. https://doi.org/10.1038/s41598-022-06067-0.

[116] Rutqvist J, Oldenburg CM. Analysis of injection-induced micro-earthquakes in a geothermal steam reservoir, the geybers geothermal field, California. Proceedings of the 42th US rock mechanics symposium. 2008. Paper No. 151, http://escholar.ship.org/uc/item/4qg7v6qz.pdf.

[117] Lasaga AC, Soler JM, Ganor J, Burch TE, Nagy KL. Chemical weathering rate laws and global geochemical cycles. Geochem Cosmochim Acta 1994;58(10):2361-86. https://doi.org/10.1016/0016-7037(94)90016-7.

[118] Elsworth D, Yasuhara H. Mechanical and transport constitutive models for fractures subject to dissolution and precipitation: mechanical and transport constitutive models. Int J Numer Anal Methods GeoMech 2010;34(5):533-49. https://doi.org/10.1002/nag.831.

[119] Min K-B, Rutqvist J, Elsworth D. Chemically and mechanically mediated influences on the transport and mechanical characteristics of rock fractures. Int J Rock Mech Min Sci 2009;46(1):80-9. https://doi.org/10.1016/j.ijrmms.2008.04.002.

[120] Ogata S, Yasuhara H, Kinoshita N, Cheon D-S, Kishida K. Modeling of coupled thermal-hydraulic-mechanical-chemical processes for predicting the evolution in permeability and reactive transport behavior within single rock fractures. Int J Rock Mech Min Sci 2018;107:271-81. https://doi.org/10.1016/j.ijrmms.2018.04.015.

[121] Andre BJ, Rajaram H. Dissolution of limestone fractures by cooling waters: early development of hypogene karst systems: dissolution of limestone fractures by cooling waters. Water Resour Res 2005;41(1). https://doi.org/10.1029/2004WR003331.

[122] Jing Z, Watanabe K, Willis-Richards J, Hashida T. A 3-D water/rock chemical interaction model for prediction of HDR/HWR geothermal reservoir performance. Geothermics 2002;31(1):1-28. https://doi.org/10.1016/S0375-6505(00)00059-6.

[123] Pandey SN, Chaudhuri A, Rajaram H, Kelkar S. Fracture transmissivity evolution due to silica dissolution/precipitation during geothermal heat extraction.
Geothermics 2015;57:111–26. https://doi.org/10.1016/j.
geothermics.2015.06.011.

[124] Taron J, Elsworth D. Thermal-hydrologic-mechanical-chemical processes in the evolution of engineered geothermal reservoirs. Int J Rock Mech Min Sci 2009;46 (5):855–64. https://doi.org/10.1016/j.ijrmms.2009.01.007.

[125] King GCP, Stein RS, Lin J. Static stress changes and the triggering of earthquakes. Bull Seismol Soc Am 1994;84(3):935–53.

[126] Stein RS. Earthquake conversations. Scientific American Sp 2005;15(2):82–9. https://doi.org/10.1038/scientificamerican0705-82sp.

[127] Toda S, Lin J, Stein RS. Using the 2011 M w 9.0 off the Pacific coast of Tohoku Earthquake to test the Coulomb stress triggering hypothesis and to calculate faults brought closer to failure. Earth Planets Space 2011;63(7):725–30. https://doi. org/10.5047/eps.2011.05.010.

[128] Brown MRM, Ge S. Small earthquakes matter in injection-induced seismicity. Geophys Res Lett 2018;45(11):5445–53. https://doi.org/10.1029/ 2018GL077472.

[129] Okada Y. Internal deformation due to shear and tensile faults in a half-space. Bull Seismol Soc Am 1992;82(2):1018–40. https://doi.org/10.1785/ BSSA0820021018.

[130] Shapiro SA, Dinske C. Stress drop, seismogenic index and fault cohesion of fluid- induced earthquakes. Rock Mech Rock Eng 2021;54(10):5483–92. https://doi. org/10.1007/s00603-021-02420-3.

[131] Goertz-Allmann BP, Wiemer S. Geomechanical modeling of induced seismicity source parameters and implications for seismic hazard assessment. GEOPHYSICS 2013;78(1):KS25–39. https://doi.org/10.1190/geo2012-0102.1.

[132] Clerc F, Harrington RM, Liu Y, Gu YJ. Stress drop estimates and hypocenter relocations of induced seismicity near Crooked Lake, Alberta. Geophys Res Lett 2016;43(13):6942–51. https://doi.org/10.1002/2016GL069800.

[133] Holmgren JM, Atkinson GM, Ghofrani H. Stress drops and directivity of induced earthquakes in the Western Canada sedimentary Basin. Bull Seismol Soc Am 2019;109(5):1635–52. https://doi.org/10.1785/0120190035.

[134] Huang Y, Ellsworth WL, Beroza GC. Stress drops of induced and tectonic earthquakes in the central United States are indistinguishable. Sci Adv 2017;3(8): e1700772. https://doi.org/10.1126/sciadv.1700772.

[135] Spottiswoode SM, McGarr A. Source parameters of tremors in a deep-level gold mine. Bull Seismol Soc Am 1975;65(1):93–112.

[136] Tomic J, Abercrombie RE, Do Nascimento AF. Source parameters and rupture velocity of small $M \le 2.1$ reservoir induced earthquakes. Geophys J Int 2009;179 (2):1013–23. https://doi.org/10.1111/j.1365-246X.2009.04233.x.

[137] Zhang J, Zhou X, Zhou L, Berto F. Progressive failure of brittle rocks with non-isometric flaws: insights from acousto-optic-mechanical (AOM) data. Fatig Fract Eng Mater Struct 2019;42(8):1787–802. https://doi.org/10.1111/ffe.13019.

[138] Abercrombie R, Leary P. Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California: implications for earthquake scaling. Geophys Res Lett 1993;20(14):1511–4. https://doi.org/10.1029/93GL00367.

[139] Boyd OS, McNamara DE, Hartzell S, Choy G. Influence of lithostatic stress on earthquake stress drops in North America. Bull Seismol Soc Am 2017;107(2): 856–68. https://doi.org/10.1785/0120160219.

[140] Chen X, Shearer PM. Comprehensive analysis of earthquake source spectra and swarms in the Salton Trough, California. J Geophys Res 2011;116(B9):B09309. https://doi.org/10.1029/2011JB008263.

[141] Chen X, Shearer PM. California foreshock sequences suggest seismic triggering process. Geophys Res Lett 2013;40(11):2602–7. https://doi.org/10.1002/ grl.50444.

[142] Fehler M, Phillips WS. Simultaneous inversion for Q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock. Bull Seismol Soc Am 1991;81(2):553–75. https://doi.org/10.1785/BSSA0810020553.

[143] Goertz-Allmann BP, Goertz A, Wiemer S. Stress drop variations of induced earthquakes at the Basel geothermal site. Geophys Res Lett 2011;38(9): 2011GL047498. https://doi.org/10.1029/2011GL047498.

[144] Hough SE. Shaking from injection-induced earthquakes in the central and Eastern United States. Bull Seismol Soc Am 2014;104(5):2619–26. https://doi.org/ 10.1785/0120140099.

[145] Hough SE. Shaking intensity from injection-induced versus tectonic earthquakes in the central-eastern United States. Lead Edge 2015;34(6):690–7. https://doi. org/10.1190/tle34060690.1.

[146] Sumy DF, Neighbors CJ, Cochran ES, Keranen KM. Low stress drops observed for aftershocks of the 2011 M w 5.7 Prague, Oklahoma, earthquake. J Geophys Res Solid Earth 2017;122(5):3813–34. https://doi.org/10.1002/2016JB013153.

[147] Yu H, Harrington RM, Kao H, Liu Y, Abercrombie RE, Wang B. Well proximity governing stress drop variation and seismic attenuation associated with Hydraulic fracturing induced earthquakes. J Geophys Res Solid Earth 2020;125(9): e2020JB020103. https://doi.org/10.1029/2020JB020103.

[148] Catalli F, Meier M-A, Wiemer S. The role of coulomb stress changes for injection-induced seismicity: the basal enhanced geothermal system: the basal enhanced geothermal system. Geophys Res Lett 2013;40(1):72–7. https://doi.org/10.1029/ 2012GL054147.

[149] Schoenball M, Baujard C, Kohl T, Dorbath L. The role of triggering by static stress transfer during geothermal reservoir stimulation: stress transfer during stimulation. J Geophys Res Solid Earth 2012;117(B9). https://doi.org/10.1029/ 2012JB009304.

[150] Kettlety T, Verdon JP, Werner MJ, Kendall JM, Budge J. Investigating the role of elasticostatic stress transfer during hydraulic fracturing-induced fault activation. Geophys J Int 2019;217(2):1200–16. https://doi.org/10.1093/gji/ggz080.

[151] Liu G, Lu R, He D, Tao W, Huang X, Su P, Xu F, Zhang W. Cascade processes of induced and triggered earthquakes-case study in the weiyuan shale gas development area in Sichuan Basin, China. Tectonophysics 2024;890:230495. https://doi.org/10.1016/j.tecto.2024.230495.

[152] Bourouis S, Bernard P. Evidence for coupled seismic and aseismic fault slip during water injection in the geothermal site of Soultz (France), and implications for seismogenic transients. Geophys J Int 2007;169(2):723–32. https://doi.org/ 10.1111/j.1365-246X.2006.03325.x.

[153] Danré P, De Barros L, Cappa F, Ampuero J. Prevalence of aseismic slip linking fluid injection to natural and anthropogenic seismic swarms. J Geophys Res Solid Earth 2022;127(12):e2022JB025571. https://doi.org/10.1029/2022JB025571.

[154] Danré P, De Barros L, Cappa F, Passarelli L. Parallel dynamics of slow slips and fluid-induced seismic swarms. Nat Commun 2014;25(1):8943. https://doi.org/ 10.1038/s41467-024-53285-3.

[155] Guglielmi Y, Cappa F, Avouac J-P, Henry P, Elsworth D. Seismicity triggered by fluid injection-induced aseismic slip. Science 2015;348(6240):1224–6. https:// doi.org/10.1126/science.aab0476.

[156] Bhattacharya P, Viesca RC. Fluid-induced aseismic fault slip outpaces pore-fluid migration. Science 2019;364(6439):464–8. https://doi.org/10.1126/science. aaw7354.

[157] De Barros L, Wynants-Morel N, Cappa F, Danré P. Migration of fluid-induced seismicity reveals the seismogenic state of faults. J Geophys Res Solid Earth 2021; 126(11). https://doi.org/10.1029/2021JB022767.

[158] Tal Y, Goebel T, Avouac J-P. Experimental and modeling study of the effect of fault roughness on dynamic frictional sliding. Earth Planet Sci Lett 2020;536: 116133. https://doi.org/10.1016/j.epsl.2020.116133.

[159] Wynants-Morel N, Cappa F, De Barros L, Ampuero J. Stress perturbation from aseismic slip drives the seismic front during fluid injection in a permeable fault. J Geophys Res Solid Earth 2020;125(7). https://doi.org/10.1029/ 2019JB019179.

[160] McGarr A, Barbour AJ. Injection-induced moment release can also be aseismic. Geophys Res Lett 2018;45(11):5344–51. https://doi.org/10.1029/ 2018GL078422.

[161] Yang Y, Dunham EM. Effect of porosity and permeability evolution on injection-induced aseismic slip. J Geophys Res Solid Earth 2021;126(7). https://doi.org/ 10.1029/2020JB021258.

[162] Cornet FH. Seismic and aseismic motions generated by fluid injections.

Geomechanics for Energy and the Environment 2016;5:42–54. https://doi.org/ 10.1016/j.gete.2015.12.003.

[163] Sáez A, Lecampion B. Post-injection aseismic slip as a mechanism for the delayed triggering of seismicity. Proc R Soc A 2023;479(2273):20220810. https://doi. org/10.1098/rspa.2022.0810.

[164] Vilarrasa V, De Simone S, Carrera J, Villaseñor A. Multiple induced seismicity mechanisms at Castor underground gas storage illustrate the need for thorough monitoring. Nat Commun 2022;13(1):3447. https://doi.org/10.1038/s41467- 022-30903-6.

[165] Jacquey AB, Viesca RC. Nucleation and arrest of fluid-induced aseismic slip. Geophys Res Lett 2023;50(4). https://doi.org/10.1029/2022GL101228.

[166] Sáez A, Lecampion B, Bhattacharya P, Viesca RC. Three-dimensional fluid-driven stable frictional ruptures. J Mech Phys Solid 2022;160:104754. https://doi.org/ 10.1016/j.jmps.2021.104754.

[167] Eyre TS, Samsonov S, Feng W, Kao H, Eaton DW. InSAR data reveal that the largest hydraulic fracturing-induced earthquake in Canada, to date, is a slow-slip event. Sci Rep 2022;12(1):2043. https://doi.org/10.1038/s41598-022-06129-3.

[168] Cornet FH, Helm J, Poitrenaud H, Etchecopar A. Seismic and aseismic slips induced by large-scale fluid injections. In: Talebi S, editor. Seismicity associated with mines, reservoirs and fluid injections. Birkhäuser Basel; 1997. p. 563–83. https://doi.org/10.1007/978-3-0348-8814-1_12.

[169] De Barros L, Guglielmi Y, Rivet D, Cappa F, Duboeuf L. Seismicity and fault aseismic deformation caused by fluid injection in decametric in-situ experiments. C R Geosci 2018;350(8):464–75. https://doi.org/10.1016/j.crte.2018.08.002.

[170] McLaskey GC, Lockner DA. Preslip and cascade processes initiating laboratory stick slip. J Geophys Res Solid Earth 2014;119(8):6323–36. https://doi.org/ 10.1002/2014JB011220.

[171] Pepin KS, Ellsworth WL, Sheng Y, Zebker HA. Shallow aseismic slip in the Delaware basin determined by Sentinel-1 InSAR. J Geophys Res Solid Earth 2022; 127(2):e2021JB023157. https://doi.org/10.1029/2021JB023157.

[172] Aretusini S, Meneghini F, Spagnuolo E, Harbord CW, Di Toro G. Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone. Nat Commun 2021;12(1):2481. https://doi.org/10.1038/s41467-021-22805-w.

[173] Dal Zilio L, Hegyi B, Behr W, Gerya T. Hydro-mechanical earthquake cycles in a poro-visco-elasto-plastic fluid-bearing fault structure. Tectonophysics 2022;838: 229516. https://doi.org/10.1016/j.tecto.2022.229516.

[174] De Barros L, Guglielmi Y, Cappa F, Nussbaum C, Birkholzer J. Induced microseismicity and tremor signatures illuminate different slip behaviours in a natural shale fault reactivated by a fluid pressure stimulation (Mont Terri). Geophys J Int 2023;235(1):531–41. https://doi.org/10.1093/gji/ggad231.

[175] Wibberley CAJ, Shimamoto T. Earthquake slip weakening and asperities explained by thermal pressurization. Nature 2005;436(7051):689–92. https:// doi.org/10.1038/nature03901.

[176] Ucar E, Berre I, Keilegavlen E. Post injection normal closure of fractures as a mechanism for induced seismicity. Geophys Res Lett 2017;44(19):9598–606. https://doi.org/10.1002/2017GL074282.

[177] McClure MW. Generation of large postinjection-induced seismic events by backflow from dead-end faults and fractures. Geophys Res Lett 2015;42(16): 6647–54. https://doi.org/10.1002/2015GL065028.
[178] Brune J, Thatcher W. International Handbook of Earthquake and Engineering Seismology International (Association of Seismology and Physics of Earth's Interior, Committee on Education 2002;81A).

[179] Rice JR, Cleary MP. Some basic stress diffusion solutions for fluid-saturated elastic porous media with compressible constituents. *Rev Geophys* 1976;14(2): 227. https://doi.org/10.1029/RG014i002p00227.

[180] Sibson RH. Interactions between temperature and pore-fluid pressure during earthquake faulting and a mechanism for partial or total stress relief. *Nat Phys Sci* (Lond) 1973;243(126):66-8. https://doi.org/10.1038/physi243066a0.

[181] Richter CF. An instrumental earthquake magnitude scale. * Bull Seismol Soc Am* 1935;25(1):1-32.

[182] Hanks TC, Kanamori H. A moment magnitude scale. *J Geophys Res* 1979;84.

[183] Kanamori H. The energy release in great earthquakes. *J Geophys Res* 1977;82 (20):2981-7. https://doi.org/10.1029/JB082i020p02981.

[184] Kanamori H. Quantification of earthquakes. *Nature* 1978;271:411-4.

[185] Mereu RF. A study of the relations between ML, Me, Mw, apparent stress, and fault aspect ratio. *Phys Earth Planet Inter* 2020;298:106278. https://doi.org/10.1016/j.pepi.2019.106278.

[186] Baek H, Chung J-B, Yun GW. Differences in public perceptions of geothermal energy based on EGS technology in Korea after the Pohang earthquake: national vs. local. *Technol Forecast Soc Change* 2021;172:121027. https://doi.org/10.1016/j.techfore.2021.121027.

[187] Schindler M, Baumgärtner J, Gandy T, Hauffe P, Hettkamp T, Menzel H, Penzkofer P, Teza D, Tischner T, Wahl G. Successful hydraulic stimulation techniques for electric power production in the Upper Rhine Graben, Central Europe. *Proceedings World Geothermal Congres* 2010;7.

[188] Riffault J, Dempsey D, Karra S, Archer R. Microseismicity cloud can be substantially larger than the associated stimulated fracture volume: the case of the paralana enhanced geothermal system. *J Geophys Res Solid Earth* 2018. https://doi.org/10.1029/2017JB015299.

[189] Riffault J, Dempsey D, Archer R, Kelkar S, Karra S. Understanding poroelastic stressing and induced seismicity with a stochastic/deterministic model: an application to an EGS stimulation at Paralana, South Australia, 2011. 41st Workshop on Geothermal Reservoir Engineering. Stanford Geothermal Workshop, SGP-TR-209 2016.

[190] Herrmann M, Kraft T, Tormann T, Scarabello L, Wiemer S. A consistent high-resolution catalog of induced seismicity in basel based on matched filter detection and tailored post-processing. *J Geophys Res Solid Earth* 2019;124(8):8449-77. https://doi.org/10.1029/2019JB017468.

[191] Kraft T, Deichmann N. High-precision relocation and focal mechanism of the injection-induced seismicity at the Basel EGS. *Geothermics* 2014;52:59-73. https://doi.org/10.1016/j.geothermics.2014.05.014.

[192] Terakawa T. Evolution of pore fluid pressures in a stimulated geothermal reservoir inferred from earthquake focal mechanisms. *Geophys Res Lett* 2014;41 (21):7468-76. https://doi.org/10.1002/2014GL061908.

[193] Terakawa T, Miller SA, Deichmann N. High fluid pressure and triggered earthquakes in the enhanced geothermal system in Basel, Switzerland: high fluid pressure in Basel. *J Geophys Res Solid Earth* 2012;117(B7). https://doi.org/10.1029/2011JB008980.

[194] Catalli F, Rinaldi AP, Gischig V, Nespoli M, Wiemer S. The importance of earthquake interactions for injection-induced seismicity: retrospective modeling of the Basel Enhanced Geothermal System. *Geophys Res Lett* 2016;43(10): 4992-9. https://doi.org/10.1002/2016GL068932.

[195] Mukuhira Y, Dinske C, Asanuma H, Ito T, Häring MO. Pore pressure behavior at the shut-in phase and causality of large induced seismicity at Basel, Switzerland. *J Geophys Res Solid Earth* 2017;122(1):411-35. https://doi.org/10.1002/2016JB013338.

[196] Andrés S, Santillán D, Mosquera JC, Cueto-Felguerero L. Thermo-poroelastic analysis of induced seismicity at the Basel enhanced geothermal system. *Sustainability* 2019;11(24):6904. https://doi.org/10.3390/su11246904.

[197] Humphreys B, Hodson-Clarke A, Hogarth R. Habanero geothermal project field development plan. *Geodynamics* Ltd; 2014.

[198] Holl HG, Barton C. Habanero field-structure and state of stress. *World Geothermal Congress* 2015:19-25.

[199] Llanos EM, Zarrouk SJ, Hogarth RA. Numerical model of the habanero geothermal reservoir, Australia. *Geothermics* 2015;53:308-19. https://doi.org/10.1016/j.geothermics.2014.07.008.

[200] McMahon A, Baisch S. Case study of the seismicity associated with the stimulation of the enhanced geothermal system at Habanero, Australia. 2013. p. 29-36.

[201] Baisch S, Weidler R, Voros R, Wyborn D, de Graaf L. Induced seismicity during the stimulation of a geothermal HFR reservoir in the cooper Basin, Australia. *Bull Seismol Soc Am* 2006;96(6):2242-56. https://doi.org/10.1785/0120050255.

[202] Wang TA, Dunham EM. Hindcasing injection-induced aseismic slip and microseismicity at the Cooper Basin Enhanced Geothermal Systems Project. *Sci Rep* 2022;12(1):19481. https://doi.org/10.1038/s41598-022-23812-7.

[203] Genter A, Fritsch DJ, Cuenot N, Baumgärtner J, Graff J. Overview of the current activities of the European EGS Soultz project: from exploration to electricity production. *Thirty-Fourth Workshop on Geothermal Reservoir Engineering; 2009*, February 9.

[204] Schill E, Genter A, Cuenot N, Kohl T. Hydraulic performance history at the Soultz EGS reservoirs from stimulation and long-term circulation tests. *Geothermics* 2017;70:110-24. https://doi.org/10.1016/j.geothermics.2017.06.003.

[205] Tischner T, Schindler M, Jung R, Nami P. HDR project Soultz: hydraulic and seismic observations during stimulation of the 3 deep wells by massive water injections. *32nd Workshop on Geothermal Engineering* 2007;7.

[206] Gaucher E, Schoenball M, Heidbach O, Zang A, Fokker PA, van Wees J-D, Kohl T. Induced seismicity in geothermal reservoirs: a review of forecasting approaches. *Renew Sustain Energy Rev* 2015;52:1473-90. https://doi.org/10.1016/j.rser.2015.08.026.

[207] Baisch S, Vörös R, Rothert E, Stang H, Jung R, Schellschmidt R. A numerical model for fluid injection induced seismicity at soultz-sous-Forêts. *Int J Rock Mech Min Sci* 2010;47(3):405-13. https://doi.org/10.1016/j.ijrmms.2009.10.001.

[208] Langenbruch C, Shapiro SA. Decay rate of fluid-induced seismicity after termination of reservoir stimulations. *GEOPHYSICS* 2010;75(6):MA53-62. https://doi.org/10.1190/1.3506005.

[209] Calò M, Dorbath C, Cornet FH, Cuenot N. Large-scale aseismic motion identified through 4-D P-wave tomography: temporal subsetting of the stimulation period. *Geophys J Int* 2011;186(3):1295-314. https://doi.org/10.1111/j.1365-246X.2011.05108.x.

[210] Lengliné O, Lamourette L, Vivin L, Cuenot N, Schmittbuhl J. Fluid-induced earthquakes with variable stress drop. *J Geophys Res Solid Earth* 2014;119(12): 8900-13. https://doi.org/10.1002/2014JB011282.

[211] Sanjuan B, Pinault J-L, Rose P, Gérard A, Brach M, Braissant G, Rouzet C, Foucher J-C, Gautier A, Touzelet S. Tracer testing of the geothermal heat exchanger at Soultz-sous-Forêts (France) between 2000 and 2005. *Geothermics* 2006;35(5-6):622-53. https://doi.org/10.1016/j.geothermics.2006.09.007.

[212] Gaucher E, Jolivet M, Peter-Borie M. Preliminary results of the seismicity induced during the stimulation of the Vendenheim enhanced geothermal System (France). *World Geothermal Congress* 2020:1-6.

[213] Abreu Torres J, Hutka G, Cacace M, Blöcher G, Magnenet V, Schmittbuhl J. Large-scale reservoir modeling of the Vendenheim geothermal site (France). https://doi.org/10.5194/egusphere-egu24-18451; 2024, March 11.

[214] Kwiatek G, Bulut F, Bohnhoff M, Dresen G. High-resolution analysis of seismicity induced at Berlin geothermal field, El Salvador. *Geothermics* 2014;52:98-111. https://doi.org/10.1016/j.geothermics.2013.09.008.

[215] Hofmann H, Zimmermann G, Farkas M, Huenges E, Zang A, Leonhardt M, Kwiatek G, Martinez-Garzon P, Bohnhoff M, Min K-B, Fokker P, Westaway R, Bethmann F, Meier P, Yoon KS, Choi JW, Lee TJ, Kim KY. First field application of cyclic soft stimulation at the Pohang Enhanced Geothermal System site in Korea. *Geophys J Int* 2019;217(2):926-49. https://doi.org/10.1093/gji/ggz058.

[216] Grigoli F, Cesca S, Rinaldi AP, Manconi A, López-Comino JA, Clinton JF, Westaway R, Cauzzi C, Dahm T, Wiemer S. The November 2017 M w 5.5 Pohang earthquake: a possible case of induced seismicity in South Korea. *Science* 2018; 360(6392):1003-6. https://doi.org/10.1126/science.aat2010.

[217] Lee K-K, Ellsworth WL, Giardini D, Townend J, Ge S, Shimamoto T, Yeo I-W, Kang T-S, Rhie J, Sheen D-H, Chang C, Woo J-U, Langenbruch C. Managing injection-induced seismic risks. *Science* 2019;364(6442):730-2. https://doi.org/10.1126/science.aax1878.

[218] Chang KW, Yoon H, Kim Y, Lee MY. Operational and geological controls of coupled poroelastic stressing and pore-pressure accumulation along faults: induced earthquakes in Pohang, South Korea. *Sci Rep* 2020;10(1):2073. https://doi.org/10.1038/s41598-020-58881-z.

[219] Yeo IW, Brown MRM, Ge S, Lee KK. Causal mechanism of injection-induced earthquakes through the Mw 5.5 Pohang earthquake case study. *Nat Commun* 2020;11(1):2614. https://doi.org/10.1038/s41467-020-16408-0.

[220] Yoo H, Park S, Xie L, Kim K-I, Min K-B, Rutqvist J, Rinaldi AP. Hydro-mechanical modeling of the first and second hydraulic stimulations in a fractured geothermal reservoir in Pohang, South Korea. *Geothermics* 2021;89:101982. https://doi.org/10.1016/j.geothermics.2020.101982.

[221] Alcolea A, Meier P, Vilarrasa V, Olivella S, Carrera J. Hydromechanical modeling of the hydraulic stimulations in borehole PX2 (Pohang, South Korea). *Geothermics* 2024;120:103009. https://doi.org/10.1016/j.geothermics.2024.103009.

[222] López-Comino JA, Cesca S, Heimann S, Grigoli F, Milkereit C, Dahm T, Zang A. Characterization of hydraulic fractures growth during the äspö hard rock laboratory experiment (Sweden). *Rock Mech Rock Eng* 2017;50(11):2985-3001. https://doi.org/10.1007/s00603-017-1285-0.

[223] Gischig V, Bethmann F, Hertrich M, Wiemer S, Mignan A, Broccardo M, Villiger L, Obermann A, Diehl T. Induced seismic hazard and risk analysis of hydraulic stimulation experiments at the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) [Application/pdf,40. ETH Zurich; 2019; p. 56. https://doi.org/10.3929/ETHZ-B-000384348. updated version].

[224] Kneafsey T, Dobson P, Blankenship D, Schwering P, White C, Morris JP, Huang L, Johnson T, Burghardt J, Mattson E, Neupane G, Strickland C, Knox H, Vermuel V, Ajo-Franklin J, Fu P, Roggenthen W, Doe T, Schoenball M, Robertson M. The EGS Collab project: outcomes and lessons learned from hydraulic fracture stimulations in crystalline rock at 1.25 and 1.5 km depth. *Geothermics* 2025;126:103178. https://doi.org/10.1016/j.geothermics.2024.103178.

[225] Moore J, McLennan J, Pankow K, Simmons S, Podgorney R, Wannamaker P, Jones C, Rickard W, Xing P. The Utah Frontier Observatory for Research in Geothermal Energy (FORGE): a laboratory for characterizing, creating and sustaining enhanced geothermal systems. *Proceedings of the 45th workshop on geothermal reservoir engineering, 2020*, February.

[226] Amann F, Gischig V, Evans K, Doetsch J, Jalali R, Valley B, Krietsch H, Dutler N, Villiger L, Brixel B, Klepikova M, Kittilä A, Madonna C, Wiemer S, Saar MO, Loew S, Driesner T, Maurer H, Giardini D. The seismo-hydro mechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment. *Solid Earth* 2018;9(1):115-37. https://doi.org/10.5194/se-9-115-2018.

[227] Gischig VS, Giardini D, Amann F, Hertrich M, Krietsch H, Loew S, Maurer H, Villiger L, Wiemer S, Bethmann F, Brixel B, Doetsch J, Doonechaly NG,
Driesner T, Dutler N, Evans KF, Jalali M, Jordan D, Kittilä A, Valley B. Hydraulic stimulation and fluid circulation experiments in underground laboratories: stepping up the scale towards engineered geothermal systems. Geomechanics for Energy and the Environment 2020;24:100175. https://doi.org/10.1016/j.gete.2019.100175.

[228] Guglielmi Y, Elsworth D, Cappa F, Henry P, Gout C, Dick P, Durand J. In situ observations on the coupling between hydraulic diffusivity and displacements during fault reactivation in shales. J Geophys Res Solid Earth 2015;120(11): 7729–48. https://doi.org/10.1002/2015JB012158.

[229] Guglielmi Y, Nussbaum C, Jeanne P, Rutqvist J, Cappa F, Birkholzer J. Complexity of fault rupture and fluid leakage in shale: insights from a controlled fault activation experiment. J Geophys Res Solid Earth 2020;125(2): e2019JB017781. https://doi.org/10.1029/2019JB017781.

[230] Ji Y, Hofmann H, Duan K, Zang A. Laboratory experiments on fault behavior towards better understanding of injection-induced seismicity in geoenergy systems. Earth Sci Rev 2022;226:103916. https://doi.org/10.1016/j.earscirev.2021.103916.

[231] Bentz S, Kwiatek G, Martínez-Garzón P, Bohnhoff M, Dresen G. Seismic moment evolution during hydraulic stimulations. Geophys Res Lett 2020;47(5). https://doi.org/10.1029/2019GL086185.

[232] Zhou W, Lanza F, Grigoratos I, Schultz R, Cousse J, Trutnevyte E, Muntendam-Bos A, Wiemer S. Managing induced seismicity risks from enhanced geothermal systems: a good practice guideline. Rev Geophys 2024;62(4):e2024RG000849. https://doi.org/10.1029/2024RG000849.

[233] Schultz R, Quitoriano V, Wald DJ, Beroza GC. Quantifying nuisance ground motion thresholds for induced earthquakes. Earthq Spectra 2021;37(2):789–802. https://doi.org/10.1177/8755293020988025.

[234] Kwiatek G, Saarno T, Ader T, Bluemle F, Bohnhoff M, Chendorain M, Dresen G, Heikkinen P, Kukkonen I, Leary P, Leonhardt M, Malin P, Martínez-Garzón P, Passmore K, Passmore P, Valenzuela S, Wollin C. Controlling fluid-induced seismicity during a 6.1-km-deep geothermal stimulation in Finland. Sci Adv 2019; 5(5):eaav7224. https://doi.org/10.1126/sciadv.aav7224.

[235] Broccardo M, Mignan A, Wiemer S, Stojadinovic B, Giardini D. Hierarchical bayesian modeling of fluid-induced seismicity. Geophys Res Lett 2017;44(22):11. https://doi.org/10.1002/2017GL075251. 357-11,367.

[236] Mignan A, Broccardo M, Wiemer S, Giardini D. Induced seismicity closed-form traffic light system for actuarial decision-making during deep fluid injections. Sci Rep 2017;7(1):13607. https://doi.org/10.1038/s41598-017-13585-9.

[237] Ritz VA, Mizrahi L, Repollés VC, Rinaldi AP, Hjörleifsdóttir V, Wiemer S. Pseudo-prospective forecasting of induced and natural seismicity in the Hengill geothermal field. Preprints 2023. https://doi.org/10.22541/essoar.168500354.49240043/v1 [Preprint].

[238] Schultz R, Baptie B, Edwards B, Wiemer S. Red-light thresholds for induced seismicity in the UK [Application/pdf] 2023:16. https://doi.org/10.3929/ETHZ-B-000648797.

[239] Zang A, Zimmermann G, Hofmann H, Stephansson O, Min K-B, Kim KY. How to reduce fluid-injection-induced seismicity. Rock Mech Rock Eng 2019;52(2): 475–93. https://doi.org/10.1007/s00603-018-1467-4.

[240] Jia Y, Tsang C-F, Hammar A, Niemi A. Hydraulic stimulation strategies in enhanced geothermal systems (EGS): a review. Geomechanics and Geophysics for Geo-Energy and Geo-Resources 2022;8(6):211. https://doi.org/10.1007/s40948-022-00516-w.

[241] Norbeck J, Latimer T, Gradl C, Agarwal S, Dadi S, Eddy E, Fercho S, Lang C, McConville E, Titov A, Voller K, Woitt M. A review of drilling, completion, and stimulation of a horizontal geothermal well system in North-Central Nevada. Proceedings of the 48th workshop on geothermal Reservoir engineering. 2023. p. 6–8.

[242] Vaezi I, Alcolea A, Meier P, Parisio F, Carrera J, Vilarrasa V. Numerical modeling of hydraulic stimulation of fractured crystalline rock at the bedretto underground laboratory for geosciences and geoenergies. Int J Rock Mech Min Sci 2024;176: 105689. https://doi.org/10.1016/j.ijrmms.2024.105689.

[243] Boyet A, De Simone S, Vilarrasa V. To bleed-off or not to bleed-off? Geophys Res Lett 2024;51(23):e2023GL107926. https://doi.org/10.1029/2023GL107926.

[244] Boyet A, Vilarrasa V, Rutqvist J, De Simone S. Forecasting fluid-injection induced seismicity to choose the best injection strategy for safety and efficiency. Philos Trans R Soc A Math Phys Eng Sci 2024;382(2275):20230179. https://doi.org/10.1098/rsta.2023.0179.

[245] Alghannam M, Juanes R. Understanding rate effects in injection-induced earthquakes. Nat Commun 2020;11(1):3053. https://doi.org/10.1038/s41467-020-16860-y.

[246] McClure MW, Horne RN. Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model. GEOPHYSICS 2011;76(6): WC181–98. https://doi.org/10.1190/geo2011-0064.1.

[247] Tangirala SK, Parisio F, Vaezi I, Vilarrasa V. Effectiveness of injection protocols for hydraulic stimulation in enhanced geothermal systems. Geothermics 2024; 120:103018. https://doi.org/10.1016/j.geothermics.2024.103018.

[248] Frash LP, Fu P, Morris J, Gutierrez M, Neupane G, Hampton J, Welch NJ, Carey JW, Kneafsey T. Fracture caging to limit induced seismicity. Geophys Res Lett 2021;48(1):e2020GL090648. https://doi.org/10.1029/2020GL090648.

[249] Madenova Y, Frash LP, Li W, Meng M, C BK, Hampton J, Xiong Q, Viswanathan HS. Fracture caging in a lab fault to prevent seismic rupture during fluid injection. Geothermics 2025;126:103206. https://doi.org/10.1016/j.geothermics.2024.103206.

[250] Norbeck J, Gradl C, Latimer T. Deployment of enhanced geothermal system technology leads to rapid cost reductions and performance improvements. https://doi.org/10.31223/X5VH8C; 2024.