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Earthquakes nucleate when large amounts of elastic energy, stored in the earth's crust, are suddenly released due to abrupt sliding over a fault. Fluid injections can reactivate existing seismogenic faults and induce/trigger earthquakes by increasing fluid pressure. Here we develop an analogous experimental system of simultaneously loaded and wetted absorbent porous paper to quantify theoretically the process of wetting‐induced earthquakes. This strategy allows us to gradually release the stored energy by provoking low intensity tremors. We identify the key parameters that control the outcome of the applied injection strategy, which include the initial stress state, fault segmentation, and segment‐activation rate. Subsequent injections, initiated at high stress levels, can drive the system faster toward its instability point, nucleating a large earthquake. Starting at low stress levels, however, they can reduce the magnitude of the natural event by at least one unit. Plain Language Summary: Understanding natural and anthropogenic seismicity is a major scientific challenge. Here we present a novel analogue fault model using absorbent porous paper, which gives new insights on earthquake mitigation. When scaled to in‐situ conditions, the porous paper model represents a natural seismic rupture of magnitude Mw = 5.9. By progressively wetting it, we simulate fluid injections in the earth's crust and draw analogies to large‐scale industrial projects. In our experiments, each injection is accompanied by tremors, which progressively release energy and modify the energy budget of the system. Without precise knowledge of the fault properties, we risk driving the system faster toward an unexpected large seismic event. However, provided that the model's key parameters–fault segmentation, segment‐activation rate, and stress state–are well known or controlled, the natural rupture can be mitigated by at least one unit. We expect that these results will facilitate risk reduction in current fluid injection projects and inspire earthquake mitigation strategies for real tectonic faults. Key Points: From an energetic point of view, absorbent porous paper can be an ideal, low‐cost surrogate rock material for studying induced seismicitySegmentation of faults and sequential fluid injection in each segment can mitigate potential earthquakes by at least one order of magnitudeWe show that fault segmentation, segment‐activation rate and stress state predominantly control the result of applied injection strategies [ABSTRACT FROM AUTHOR]

Earthquake swarms are most commonly composed of small‐magnitude earthquakes. However, a recent study by Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) analyzed a swarm beneath the Noto Peninsula in Japan that, after more than two years of moderate‐magnitude seismicity, triggered the moment magnitude (Mw) 6.2 Suzu mainshock in May 2023. Based on high‐precision earthquake locations and a slip inversion of the mainshock, these authors found that the Mw 6.2 Suzu earthquake occurred on the updip extension of a fault that was active during the swarm, likely driven by increased fluid pressure. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby on 1 January 2024. These events underscore the potential for swarms to be precursors to large, damaging earthquakes. Forecasting the eventual evolution of swarms is currently very challenging but could be aided in the future by new observations and models. Plain Language Summary: Although earthquake swarms often only contain small earthquakes, occasionally they can trigger large, damaging earthquakes. Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) examined the triggering of a magnitude 6.2 earthquake in Japan, which caused extensive damage, following two years of smaller earthquakes. This sequence, like many swarms, may have been driven by elevated fluid pressure migrating upwards within the crust. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby. Forecasting the eventual evolution of ongoing swarms is currently very challenging but could be aided in the future by new observations and models. Key Points: Earthquake swarms can be precursors to damaging earthquakes, including the 1 January 2024, Mw 7.5 Noto Peninsula, Japan eventFluid pressure changes often drive swarm activity, and their degree of confinement may influence swarm evolutionDirect observations of fluids in fault zones combined with numerical modeling may aid swarm forecasting in the future [ABSTRACT FROM AUTHOR]

As the world's glaciers recede in response to a warming atmosphere, a change in the magnitude and frequency of related hazards is expected. Among the most destructive hazards are glacier lake outburst floods (GLOFs), and their future evolution is concerning for local populations and sustainable development policy. Central to this is a better understanding of triggers. There is a long‐standing assumption that earthquakes are a major GLOF trigger, and seismic activity is consistently included as a key hazard assessment criterion. Here, we provide the first empirical evidence that this assumption is largely incorrect. Focusing on the Tropical Andes, we show that, of 59 earthquakes (1900–2021) the effects of which intersect with known glacier lakes, only one has triggered GLOFs. We argue that, to help develop climate resilient protocols, the focus for future assessments should be on understanding other key GLOF drivers, such as thawing permafrost and underlying structural geology. Plain Language Summary: Climate change is increasing glacier melt in high mountains and increasing the size and number of glacial lakes. Over time, these lakes may drain catastrophically to generate glacier lake outburst floods (GLOFs), which can devastate downstream communities and destroy valuable infrastructure such as roads, bridges, and hydroelectric power facilities. As a result, many risk assessments have been carried out to understand what the triggers of GLOFs might be, in order to better predict their occurrence. One of the main triggers has been assumed to be earthquakes, but this association has not been properly tested. In this paper, we use earthquake and GLOF data from the Peruvian and Bolivian Andes to test this and find that there is little association between earthquakes and GLOFs. We conclude by arguing that focus needs to be on other GLOF triggers, and earthquake activity should be used as a secondary – not primary – indicator in GLOF susceptibility studies. Key Points: Glacier lake outburst floods (GLOFs) are a major risk concern, with earthquakes being commonly considered effective triggers in hazard assessmentsOf 59 earthquakes (1900–2021), the effects of which intersect lakes in the Tropical Andes, only one triggered GLOFsWe suggest that earthquake activity should be used as a secondary – not primary – susceptibility indicator for GLOFs [ABSTRACT FROM AUTHOR]

Using new continuous geodetic time series, we identify five shallow slow slip events (SSEs) offshore and beneath the Osa peninsula in southern Costa Rica. An early event was detected by one station in 2013, and two events occurring in close succession in both 2018 and 2022 were detected by multiple stations, indicating a preliminary recurrence interval of ∼4–5 years. While SSEs have been observed to the northwest at Nicoya, this is their first documentation in southern Costa Rica. Modeled slip distributions of the 2018 and 2022 events indicate they likely ruptured the same or overlapping patches of the plate interface, near the trench, updip of the 1983 Mw 7.4 Osa event. Immediately offshore, estimated cumulative slip from the 2018 and 2022 events is sufficient to close the slip deficit from tectonic loading over the recurrence interval, potentially limiting the magnitude and spatial slip distribution of future large ruptures. Plain Language Summary: Slow slip events (SSEs), effectively slow earthquake ruptures, are a phenomena that have been observed in many subduction zones around the world. While SSEs in subduction zones are often observed at depth, this is likely due to our observational capability being better when the events occur under land. By contrast, shallow events are more difficult to observe because they often occur under the ocean, despite their potential relationship to large, damaging, and/or tsunamigenic earthquakes. In this paper, we present research that identifies shallow slow slip events in a location where they have not been previously observed, the Osa Peninsula in southern Costa Rica. In total we observe five shallow SSEs, sometimes occurring in pairs, that appear to rupture every ∼4–5 years. Additionally we suggest that the amount of slip in these events may be sufficient to account for all the tectonic convergence in some locations, potentially limiting the size of future large earthquakes. Key Points: We identify five slow slip events in southern Costa Rica, one in 2013, and two events occurring in close succession in both 2018 and 2022The recent four events likely ruptured the same shallow patch of the megathrust, extremely close to the Middle American TrenchEvents in 2018 and 2022 seem to release nearly all slip accumulated by plate motion over a ∼4 year recurrence interval in some locations [ABSTRACT FROM AUTHOR]

We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters. Plain Language Summary: On 6 February 2023, the south‐central Türkiye was hit by two major earthquakes with magnitudes of Mw 7.8 and Mw 7.6 respectively. Among them, the complex rupture process and unexpected ground motion of the Mw 7.8 event attracted the attention of seismologists. In this paper, the 3D dynamic rupture process of this mainshock is simulated based on complex multi‐fault system and heterogeneous initial stress. And the simulation results are in good agreement with the observations. Our results show that high initial stress is required for the EAF to be triggered. The supershear rupture occurred only in certain fault segments and is unable to sustain itself in a significant area on the fault due to the along‐strike variations in fault geometry and strength. More importantly, the dynamic model suggests that we must be alert to the risk of major fault being triggered by earthquakes on nearby small faults, especially when there are seismic gaps on the major fault. Key Points: The high initial stress accumulated in the seismic gap leads to the successful triggering of the East Anatolian FaultThe change of fault geometry in the southwest segment prevented the sustained supershear ruptureThe risk of earthquake nucleation on the secondary fault triggering the major fault rupture and the related disaster was highlighted [ABSTRACT FROM AUTHOR]

Both volcano‐tectonic (VTs) and deep long‐period earthquakes (DLPs) have been documented at Akutan Volcano, Alaska and may reflect different active processes helpful for eruption forecasting. In this study, we perform high‐resolution earthquake detection, classification, and relocation using seismic data from 2005 to 2017 to investigate their relationship with underlying magmatic processes. We find that the 2,787 VTs and 787 DLPs are concentrated above and below the inferred magma reservoir respectively. They both are clustered as swarms and occur preferentially during inflation episodes with no spatial migrations. However, moment release rates of DLP swarms show a stronger correlation with inflation and their low‐frequency content is likely a source instead of a path effect. Therefore, we infer that DLPs are directly related to unsteady magma movement through a complex pathway. In comparison, repeating events are observed in VTs. Thus, we conclude that they represent fault rupture triggered by magma/fluid movement or larger earthquakes. Plain Language Summary: Volcano eruption forecasting is a challenging task that often requires the deciphering of processes underlying observed signs of volcanic unrest. As seismometers become common monitoring sensors on volcanoes, the recorded ground motion is valuable for scientists to study eruption precursors. Earthquakes are commonly observed and generally inferred to be associated with stress perturbations in the shallow crust. However, earthquakes with predominantly lower‐frequency energy are sometimes observed at depth and their origin is enigmatic. In this paper, we use the existing catalog of earthquakes at Akutan Volcano in Alaska between 2005 and 2017 as templates to successfully detect more earthquakes before locating them with higher precision. We find that earthquakes at Akutan Volcano tend to occur in swarms during times when the ground inflates due to magma accumulation beneath the volcano. Some earthquakes have predominantly low‐frequency energy which suggests a different source mechanism compared to regular earthquakes. Furthermore, the largest events are more strongly correlated with surface inflation. Therefore, we conclude that these lower‐frequency earthquakes are more directly related to unsteady magma movement through a complex pathway compared to regular earthquakes which represent fault rupture triggered by magma/fluid movement or larger earthquakes. Key Points: Moment release rates of deep long‐period events correlate more strongly with inflation episodes compared to volcano‐tectonic eventsAkutan deep long‐period earthquakes are likely due to non‐stationary source effects like unsteady magma transport through complex pathwaysAkutan volcano‐tectonic earthquakes represent fault ruptures triggered by magma/fluid movements or larger earthquakes [ABSTRACT FROM AUTHOR]

The Puebla‐Morelos (Mexico) 2017 earthquake nucleated ∼250 km inland from the trench within the Cocos oceanic plate mantle. Here, we argue that the Puebla‐Morelos (Mexico) 2017 earthquake resulted from changes in effective stress due to the reaction brucite + antigorite = olivine + H2O leading to the reactivation of pre‐existing seafloor faults. Fluid release (∼185 kg of H2O per m3 of subducted hydrated harzburgite) and volume increase (ΔVrsolid+fluid = ∼0.8%) likely occur along subducted seafloor‐inherited faults. The amount of H2O released, and magnitude of volume change depends on the degree of faults hydration; only highly hydrated (>40% of hydration) faults will stabilize brucite and experience this reaction at depth. The brucite + antigorite dehydration reaction may be key for intermediate seismicity worldwide. Plain Language Summary: The Puebla‐Morelos (central Mexico) Mw7.1 earthquake occurred in an uncommon locality in Mexico compared to most of the catastrophic earthquakes that have occurred in this part of the world—it nucleated ∼250 km inland, almost below Mexico City. In this paper, we explore the role of mineralogical changes occurring in the Cocos tectonic plate, which is currently descending below the North America plate. Our model tracked the changes in the minerals within the rocks and show that the earthquake might have been triggered by the physical changes associated with the mineral reaction: brucite + antigorite = olivine + H2O. We suggest that this mineral reaction primarily occurred along faults in the subducting oceanic floor along which the mantle lithosphere was hydrated prior to subduction. The brucite + antigorite dehydration reaction may be key for intermediate seismicity worldwide. Key Points: The dehydration of antigorite + brucite has a positive total volume change and leads to fluid‐induced fault reactivationWe hypothesize that fluid‐induced fault reactivation triggered the Puebla‐Morelos 2017 earthquakeThe antigorite + brucite reaction only happens in highly hydrated regions of the upper lithospheric mantle [ABSTRACT FROM AUTHOR]

The geometry of continental fault systems, and more specifically the spatial organization of faults, is a central topic to understand how earthquake ruptures start, propagate, and stop. By exploring the origin of unexpected high frequency emission during earthquakes, Chu et al. (2021), (https://doi.org/10.1029/2021GL095271) show that the most likely source for these emissions is the interaction between nearby misaligned faults. Thus, this result emphasizes the discrete nature of the strike‐slip fault segments at seismogenic crustal scale, adding to a set of evidence for spatially structured fault systems drawn from independent observations in geophysics and geology. This observation should bring some new constrains to earthquake rupture scenario by limiting the range of possible ruptures included in these models. Plain Language Summary: The geometry of faults at depth remains difficult to document, although it exerts a critical influence on the way earthquakes propagate along faults. In the case of continental strike‐slip faults, a long‐lasting discussion questions if the ground surface complexity is matched by similar complexity at depth, or conversely, if the strike‐slip geometry at depth is smoother. In this paper Chu et al. (2021), (https://doi.org/10.1029/2021GL095271) bring additional evidence of the fault structural complexity. Such evidence could be related to other independent observations pointing in a similar direction of the existence of a specific spatial scaling for strike‐slip fault structures. Such scaling should be considered in the development of seismic hazard models. Key Points: Chu et al. (2021) interpret high‐frequency in earthquake spectrum as fault geometry signatureIndependent observations from various earthquake research fields hint at spatial structure of strike‐slip faultsThe spatial structure of strike‐slip fault should be included in earthquake rupture scenario [ABSTRACT FROM AUTHOR]

Several experiments and field observations have demonstrated seismic waves‐induced permeability increases. However, a few experiments have revealed significant decreases in the permeability of fractured sandstone after shaking produced by dynamic stresses. In this paper, we analyze the tidal responses of the water level in two wells (Junan and Dingyuan) situated on and near, respectively, the Tan‐Lu fault in China. The results sampled by a single well indicate that seismic waves could both increase and decrease the permeability. In addition, our results indicate that the earthquakes that decreased the permeability in a single well were distributed in certain azimuthal zones. Given the azimuthal distribution of distant earthquakes, the observed permeability decrease could be attributed to the seismic wave‐induced clogging of fractures that compose the flow paths in the shallow crust. Our research contributes to an enhanced overall understanding of the effects of earthquakes on the permeability of the shallow crust. Plain Language Summary: Most hydrological phenomena caused by earthquakes can be explained by permeability changes. Many experiments and field observations have demonstrated coseismic increases in permeability. However, coseismic decreases in permeability have seldom been reported. In this paper, we analyze the tidal responses of the water level in two wells. The results indicate that seismic waves could both increase and decrease the permeability. In addition, we find that the earthquakes that decreased the permeability in a single well were distributed in certain azimuthal zones. Given the azimuthal distribution of distant earthquakes, the observed permeability decrease could be attributed to the seismic wave‐induced clogging of fractures that compose the flow paths in the shallow crust. Furthermore, we discuss the possible process of particle remobilization in a natural fracture network caused by seismic waves, as this process may be used to explain the azimuthal distribution of earthquakes that decreased the permeability. Our research contributes to an enhanced overall understanding of the effects of earthquakes on the crustal permeability. In the future, earthquake‐induced increases and decreases in permeability should be considered when discussing controls on permeability for exploring underground resources of groundwater, geothermal energy, oil and gas, and for safely storing nuclear and toxic waste underground. Key Points: Seismic waves could decrease besides increase the crustal permeabilityDecreases in permeability may depend on the earthquake azimuthThe decrease in the permeability could be attributed to the clogging of fractures [ABSTRACT FROM AUTHOR]

An outstanding question for induced seismicity is whether the volume of injected fluid and/or the spatial extent of the resulting pore pressure and stress perturbations limit rupture size. We simulate ruptures with and without injection‐induced pore pressure perturbations, using 2‐D dynamic rupture simulations on rough faults. Ruptures are not necessarily limited by pressure perturbations when (1) background shear stress is above a critical value, or (2) pore pressure is high. Both conditions depend on fault roughness. Stress heterogeneity from fault roughness primarily determines where ruptures stop; pore pressure has a secondary effect. Ruptures may be limited by fluid volume or pressure perturbation extent when background stress and fault roughness are low, and the maximum pore pressure perturbation is less than 10% of the background effective normal stress. Future work should combine our methodology with simulation of the loading, injection, and nucleation phases to improve understanding of injection‐induced ruptures. Plain Language Summary: Earthquakes can be induced or triggered by fluid injected deep underground, if the fluid encounters faults. Previous studies of induced seismicity at different injection sites around the world have empirically found that in many cases the maximum magnitude earthquake is found to scale with total volume of injected fluid. However, this is not always the case, and the level and heterogeneity of preexisting stress on faults likely plays an important role in determining the final earthquake size. In this paper, we use numerical simulations of earthquakes to quantify one source of stress heterogeneity—that arising from geometric roughness—and study how changes in pore pressure and stress from fluid injection interact with preexisting stress to influence earthquake size. We find that earthquakes are not limited by the injected volume, except under specific conditions. Instead, earthquakes stop where preexisting conditions are unfavorable for continued rupture; in our case because of bends in the fault geometry. Earthquakes can well exceed the predicted maximum magnitude, depending on the preexisting stress on the fault, how rough it is, and the magnitude and extent of the perturbation from injection. Key Points: Rupture size is not necessarily limited by the volume of injected fluid in earthquake simulations with imposed pore pressure perturbationsStress heterogeneity arising from geometric roughness may be the primary cause for rupture termination on rough faultsHigh initial shear stress or pore pressure can trigger a rupture larger than the volume‐based magnitude limit on faults with low roughness [ABSTRACT FROM AUTHOR]

In the Nazca‐South American subduction zone, the subducted slab is flattened beneath northern Andes, called the Peruvian flat slab. The 2019 Mw 8.0 northern Peru intermediate‐depth normal‐faulting earthquake occurred at the leading edge of the Peruvian flat slab, where the slab rebends and sinks into greater depths. Here we investigate this earthquake by back projection analysis and finite fault inversion using seismic waveforms at teleseismic distances. The rupture process indicates that this earthquake ruptured mainly along strike (353°) ~150 km north‐northwestward within ~55 s (average rupture velocity ~2.7 km/s), resulting in two major slip areas with three high slip rate areas, which are consistent with three high‐frequency energy radiation subevents. Our study suggests that such a heterogeneous rupture may be caused by slab bending forces and dehydration embrittlement associated with morphology of the slab. Plain Language Summary: In the subduction zone, the oceanic plate and the continental plate converge, and then the oceanic plate subducts beneath the continental plate and sinks into great depths. In South America, the subducted oceanic plate is flattened beneath northern Peru instead of steeply sinking, called the Peruvian flat slab. After flattened, the oceanic plate starts to sink again. In the region where the oceanic plate starts to sink again, an earthquake with magnitude of 8.0 occurred at a depth of ~120 km on 26 May 2019. How and why this earthquake occurred at such a depth? Does the occurrence of this earthquake is related to the subducted oceanic plate? We try to answer these questions in this paper. By using two techniques, we obtained a scenario about this earthquake: In the region where the oceanic plate starts to sink again, the water in the oceanic plate releases, along with the effect of sinking to cause this earthquake. After this earthquake initiated, it ruptured mainly unilaterally north‐northwestward ~150 km with a speed of ~2.7 km/s, resulting in two large slip areas with three high slip rate areas. Such an uneven rupture may be produced by the heterogeneous structure of the slab. Key Points: Rupture process of the 26 May 2019 northern Peru earthquake is obtained from back projection analysis and finite fault inversionThe effects of slab bending forces and dehydration embrittlement together may cause this earthquake at an intermediate depthThis intermediate‐depth earthquake is probably associated with morphology of the Peruvian flat slab [ABSTRACT FROM AUTHOR]

In the Nazca‐South American subduction zone, the subducted slab is flattened beneath northern Andes, called the Peruvian flat slab. The 2019 Mw 8.0 northern Peru intermediate‐depth normal‐faulting earthquake occurred at the leading edge of the Peruvian flat slab, where the slab rebends and sinks into greater depths. Here we investigate this earthquake by back projection analysis and finite fault inversion using seismic waveforms at teleseismic distances. The rupture process indicates that this earthquake ruptured mainly along strike (353°) ~150 km north‐northwestward within ~55 s (average rupture velocity ~2.7 km/s), resulting in two major slip areas with three high slip rate areas, which are consistent with three high‐frequency energy radiation subevents. Our study suggests that such a heterogeneous rupture may be caused by slab bending forces and dehydration embrittlement associated with morphology of the slab. Plain Language Summary: In the subduction zone, the oceanic plate and the continental plate converge, and then the oceanic plate subducts beneath the continental plate and sinks into great depths. In South America, the subducted oceanic plate is flattened beneath northern Peru instead of steeply sinking, called the Peruvian flat slab. After flattened, the oceanic plate starts to sink again. In the region where the oceanic plate starts to sink again, an earthquake with magnitude of 8.0 occurred at a depth of ~120 km on 26 May 2019. How and why this earthquake occurred at such a depth? Does the occurrence of this earthquake is related to the subducted oceanic plate? We try to answer these questions in this paper. By using two techniques, we obtained a scenario about this earthquake: In the region where the oceanic plate starts to sink again, the water in the oceanic plate releases, along with the effect of sinking to cause this earthquake. After this earthquake initiated, it ruptured mainly unilaterally north‐northwestward ~150 km with a speed of ~2.7 km/s, resulting in two large slip areas with three high slip rate areas. Such an uneven rupture may be produced by the heterogeneous structure of the slab. Key Points: Rupture process of the 26 May 2019 northern Peru earthquake is obtained from back projection analysis and finite fault inversionThe effects of slab bending forces and dehydration embrittlement together may cause this earthquake at an intermediate depthThis intermediate‐depth earthquake is probably associated with morphology of the Peruvian flat slab [ABSTRACT FROM AUTHOR]

A numerical study of the effects of seismically generated acoustic waves in the ionosphere is conducted using a three‐dimensional (3‐D) ionospheric model driven by an axisymmetric neutral atmospheric model. A source consistent with the 2011 Tohoku earthquake initial ocean surface uplifting is applied to simulate the subsequent responses. Perturbations in electron density, ion drift, total electron content (TEC), and ground‐level magnetic fields are examined. Results reveal strong latitude and longitude dependence of ionospheric TEC, and of ground‐level magnetic field perturbations associated with acoustic wave‐driven ionospheric dynamo currents. Results also demonstrate that prior two‐dimensional models can capture dominant meridional responses of TEC over latitude, even though dynamics at other longitudes are not resolved. Conclusions support that TEC and magnetic signatures can arise from nonlinear acoustic waves generated by strong earthquakes; simulations elucidate the comprehensive physics of their 3‐D ionospheric responses. Plain Language Summary: This paper reports new numerical model results on how the ionosphere—the ionized, conducting region of the upper‐atmosphere—responds to strong acoustic waves launched by earthquakes. The effects of these waves in the ionosphere can be observed from ground: They are measured as variations in Global Positioning System satellite signals received at the ground, which translate to variations in integrated electron content of the ionosphere. They can be detected also via small fluctuations in magnetic field, which are driven by ionospheric currents. The model results suggest that both measurement techniques can provide insight into the waves and their sources; new guidance for interpreting these measurements is provided. Further, results demonstrate a new capability for simulating these processes in three dimensions, which can be applied to more‐realistic case studies. Key Points: Earthquake‐driven TEC and magnetic perturbations are studied with a 3‐D modelMagnetic fluctuations driven by infrasonic acoustic waves are detectableLocal geomagnetic field geometry affects directionality of TEC responses [ABSTRACT FROM AUTHOR]

Abstract: Focal mechanisms of induced earthquakes reflect anthropogenic contributions to preexisting geological features and fault slippages. In this paper, we examine fault‐related (double‐couple (DC)) and possibly fluid‐related (non‐double‐couple (non‐DC)) mechanisms of induced earthquakes (M2–6) at regional scales. We systematically compare well‐resolved focal mechanisms of 33 events in the Western Canada Sedimentary Basin, among which 12 were induced by hydraulic fracturing and one by secondary recovery. Most of the seismicity is dominated by strike‐slip/thrust faulting regimes, whereas limited (but consistent) non‐DC components are obtained from injection‐induced seismicity in central Alberta. We interpret the persistent compensated‐linear‐vector‐dipole components (M2.1–3.8) as reflecting fracture growth and/or noncoplanar faults slippages during hydraulic‐fracturing stimulations. We further expand the moment tensor decomposition analysis to four representative classes of induced seismicity globally and find that the overall contribution of non‐DC components is comparable between induced and tectonic earthquakes. [ABSTRACT FROM AUTHOR]

In this paper we examine a short‐lived aseismic slip episode which began immediately following the 2016 Kaikōura earthquake in the South Island of New Zealand. Using synthetic aperture radar data, we form an interferometric synthetic aperture radar time series over the epicentral region of the Kaikōura mainshock. Immediately following the earthquake, we observe 150 mm of localized uplift over an ∼25‐km2 region which is best explained by an increase in pore pressure within a shallow fluid trap as a result of a coseismic permeability change. After the initial uplift stops, deformation becomes focused along a NE‐SW trending discontinuity which cuts through the uplifted region. The fault lies within a large (∼−4 MPa) stress shadow induced by the coseismic stress change suggesting that failure should be inhibited. However, a reduction in the effective normal stress caused by the local pore pressure increase was sufficient to induce a short‐lived aseismic slip episode. Plain Language Summary: Pore fluid pressure plays a critical role in fault behavior. As the pressure increases, the stresses which help prevent the fault from breaking are reduced making it easier for the fault to move. In this study, we use interferometric synthetic aperture radar data to measure an aseismic slip (no earthquakes) episode within the epicentral region of the 2016 Kaikoura earthquake in New Zealand. Localized uplift observed immediately after the earthquake was likely caused by a pore pressure increase within a shallow fluid trap as a result of a coseismic permeability change. The observed uplift rapidly dissipates with displacements becoming focused along a NE‐SW trending fault. Because of the position and orientation of the fault relative to the Kaikoura rupture, slip along the fault would have been inhibited by the Kaikoura stress change. However, because of the local increase in pore pressure, the fault was able to move over a period of a few weeks without generating detectable seismic energy until the pore pressure dissipated and the fault relocked. Based on these observations and scaled to larger displacement episodes, along‐strike variations in fluid budget could explain the changes in fault behavior observed along larger fault systems. Key Points: Localized postseismic uplift was induced by pressurized fluids within shallow trapLarge increase in pore pressure was sufficient to trigger an aseismic slip episodeRapid relocking of the fault is consistent with pore fluid diffusion [ABSTRACT FROM AUTHOR]