Explore the vast range of titles available.

A seismic swarm affected the 53.3°–54.3° Latitude North section of the Mid‐Atlantic Ridge from 26 September to 10 December 2022. We rely on regional, teleseismic and array data to relocate 61 hypocenters and derive 77 moment tensors. The 2022 swarm released a cumulative moment equivalent to Mw 6.3. Seismicity was shallow (7 ± 3 km depth). Most earthquakes are located along the ridge axis with typical, NS oriented normal faulting mechanisms, but a few among the largest and latest earthquakes have unusual thrust mechanisms and locations as far as ∼25 km from the ridge. We attribute the swarm to a shallow magmatic intrusion, with a vertical dike first propagating ∼60 km along axis, accompanied by shallow normal faulting, and then thickening and triggering thrust earthquakes off the ridge, in response to compressive stress buildup. The unrest provides a rare example of an energetic, magmatic driven swarm episode at the mid‐ocean ridge. Plain Language Summary The largest plate boundary systems on Earth are Mid‐ocean ridges (MOR), where the plates continuously drift apart and new lithosphere is constantly being formed. Although the process is well understood, we rarely detect spreading events at MOR, mainly because these regions are remote and local monitoring is rarely possible. In September–November 2022 a large, unusual seismic swarm occurred along a spreading center ridge segment of the North Mid‐Atlantic Ridge. Despite the remoteness of the region, we managed to model regional and teleseismic data to perform earthquake relocation, depth estimation and moment tensor inversion. In this way, we could reconstruct the geometry and the evolution of the seismicity. We found that in the early days of the swarm, seismicity migrated unilaterally over ∼60 km along the ridge axis, from North to South, triggering normal faulting earthquakes, which are typical at MOR. Later, large thrust mechanisms, anomalous in an extensional environment, appeared and quickly became predominant. We explain seismological observations by a magmatic intrusion, which first propagated southward, producing shallow normal faulting earthquakes above the vertical magma dike, and later thickened, increasing compressional stresses on its sides, and triggering large thrust earthquakes. Key Points Analysis of a short, intense seismic swarm at the Mid‐Atlantic Ridge Identification of unusual, thrust focal mechanisms in an extensional environment Swarm triggered by dike intrusion at the mid‐ocean ridge

The Rhenish Massif in Central Europe, which includes the Eifel Volcanic Fields, has shown ongoing ground deformation and signs of possible unrest. A buoyant plume exerting uplift forces at the bottom of the lithosphere was proposed to explain such deformation; the hypothesis of (possibly concurrent) melt accumulation in the crust/lithospheric mantle has not been explored yet. Here, we test deformation models in an elastic half‐space considering sources of varying aspect ratio, size and depth. We explore the effects of data coverage, noise and uncertainty on the inferred source parameters. We find that the observed deformation would require melt accumulation in sub‐horizontal sill‐like structures expanding at the rate of up to ∼0.045 km3/yr. We discuss feasibility, limitations and possible interpretations of our resulting models and elaborate on further observations which may help constrain the structure of the Rhenish Massif magmatic system. Plain Language Summary Geodetic observations over the last 20 years recorded small but steady ground deformation over a wide area centered on the Eifel Volcanic Fields, Germany, where volcanism has occurred as recently as 11,000 years ago. Together with geophysical and geochemical evidences of possible ongoing unrest, the observed deformation has renewed interest over the origin of volcanism in the region. The deformation has been tentatively related to a buoyant plume in the asthenosphere. Here, we test whether the deformation may be, at least partially, originating in the lithosphere. We find that deformation data would be consistent with melt intrusions in one or more horizontal lenses located in the lithosphere, but limitations exist due to models simplifications. We discuss feasibility, limitations and possible interpretations of our results, and what additional data may improve our knowledge on the underlying magmatic system. Key Points We explore the hypothesis that the ongoing uplift in the Rhenish Massif is (partly) due to melt accumulating in the lithosphere Observed ground deformation would require the intrusion of up to ∼0.045 km3/yr into one or more horizontal magma lenses We test different deformation sources and discuss the feasibility, limitations and possible interpretations of the resulting models

Enhanced geothermal systems (EGSs) provide a potentially clean and abundant energy source. However, two magnitude-5 earthquakes recently occurred in South Korea during EGS site development. Grigoli et al. and Kim et al. present seismic and geophysical evidence that may implicate the second of these earthquakes, which occurred in Pohang, as an induced event. The combination of data from a local seismometer network, well logs, satellite observations, teleseismic waveform analysis, and stress modeling leads to the assessment that the earthquake was probably or almost certainly anthropogenically induced. The possibility remains that the earthquake occurred coincidentally at the EGS site location, but the aftershock distribution and other lines of evidence are concerning for future development of this geothermal resource. Science , this issue p. 1003 , p. 1007 Last year’s Pohang, South Korea, earthquake was potentially an induced earthquake from an enhanced geothermal system. The moment magnitude ( M w ) 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area.

The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten‐month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone‐shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp‐anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW‐NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore‐pressure perturbations and the re‐distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable. Key Points Seismicity is clustered in a cone‐shaped volume beneath Kolumbo; the cone's tip coincides with a melt reservoir at 2–4 km depth Seismicity swarms occupy nearby, yet different portions of the crust, ruling out an origin on a single fault Swarms were likely triggered by a combination of fluid pressure perturbations and redistribution of elastic stresses

Although spin fluctuations are believed to have an important role in the mechanism responsible for high-temperature superconductivity, it has been unclear whether the strength of their coupling with fermionic quasiparticles is sufficiently strong. Systematic analysis of angle-resolved photoemission and neutron spectra suggests it is. Theories based on the coupling between spin fluctuations and fermionic quasiparticles are among the leading contenders to explain the origin of high-temperature superconductivity, but estimates of the strength of this interaction differ widely 1 . Here, we analyse the charge- and spin-excitation spectra determined by angle-resolved photoemission and inelastic neutron scattering, respectively, on the same crystals of the high-temperature superconductor YBa 2 Cu 3 O 6.6 . We show that a self-consistent description of both spectra can be obtained by adjusting a single parameter, the spin–fermion coupling constant. In particular, we find a quantitative link between two spectral features that have been established as universal for the cuprates, namely high-energy spin excitations 2 , 3 , 4 , 5 , 6 , 7 and ‘kinks’ in the fermionic band dispersions along the nodal direction 8 , 9 , 10 , 11 , 12 . The superconducting transition temperature computed with this coupling constant exceeds 150 K, demonstrating that spin fluctuations have sufficient strength to mediate high-temperature superconductivity.

A crucial issue to characterize hydraulic fractures is the robust, accurate and automated detection and location of acoustic emissions (AE) associated with the fracture nucleation and growth process. Waveform stacking and coherence analysis techniques are here adapted using massive datasets with very high sampling (1 MHz) from a hydraulic fracturing experiment that took place 410 m below surface in the Äspö Hard Rock Laboratory (Sweden). We present the results obtained during the conventional, continuous water injection experiment Hydraulic Fracture 2. The resulting catalogue is composed of more than 4000 AEs. Frequency–magnitude distribution from AE magnitudes (MAE) reveals a high b value of 2.4. The magnitude of completeness is also estimated approximately MAE 1.1, and we observe an interval range of MAE between 0.77 and 2.79. The hydraulic fractures growth is then characterized by mapping the spatiotemporal evolution of AE hypocentres. The AE activity is spatially clustered in a prolate ellipsoid, resembling the main activated fracture volume (~105 m 3 ), where the lengths of the principal axes ( a  = 10 m; b  = 5 m; c  = 4 m) define its size and its orientation can be estimated for a rupture plane (strike ~123°, dip ~60°). An asymmetric rupture process regarding to the fracturing borehole is clearly exhibited. AE events migrate upwards covering the depth interval between 404 and 414 m. After completing each injection and reinjection phase, the AE activity decreases and appears located in the same area of the initial fracture phase, suggesting a crack-closing effect.

Volcanic and seismic unrest on the Reykjanes Peninsula in SW Iceland that started in late 2019 after ∼800 years of quiescence has drawn wide interest to this on‐land extension of the Mid‐Atlantic spreading ridge. Here, we use seismic data collected across the larger Peninsula region, covering six volcanic systems and associated high‐temperature geothermal areas to produce a crustal‐scale shear‐wave velocity model. The model is constructed from receiver functions (RF), and pre‐existing surface wave dispersion measurements from recent studies, supplemented with new inter‐station paths from recent seismic deployments. We compare our velocity model to RF stacks which highlight seismic discontinuity boundaries. Results show local seismicity and geothermal systems are limited to the upper crust, which is split into an upper region of extrusive‐dominated heavily fractured material <3 km and intrusive‐dominated more cohesive material below. The gabbroic lower‐crust is dominated by cumulates beyond 10 km depth, which are particularly high‐velocity west offshore of the Peninsula. Crustal thicknesses increase from 15 to 20 km eastwards, likely reflecting increasing temperature and active‐upwelling toward the center of the Iceland hotspot. Reported magma storage depths, for current and historic eruptions, generally sit within the lower‐crust, but several, including for the 2021 Fagradalsfjall eruption, indicate sub‐Moho storage, sourced from a seismically slow region we observe extending to 25 km, which is interpreted as representing a partially molten crust‐mantle transitional region. Our seismic imaging of the Reykjanes Peninsula crust gives insight into regional crustal structure and tectonic processes, as well as providing large‐scale context for the continuing volcano‐tectonic unrest the region is experiencing. Plain Language Summary Since 2019 several volcanic eruptions, and thousands of earthquakes (most too small to feel) linked to magma movement underground and near‐surface cracking, have happened on the Reykjanes Peninsula in southwest Iceland, close to the capital city Reykjavik. We use large earthquakes happening 1000s of km away from Iceland, as well as ground‐vibrations caused by surrounding oceans, to create images of the subsurface extending tens of km beneath this active region. Our area of analysis covers the whole of the Peninsula, including several other near‐by volcanic systems and geothermal areas. We find local earthquakes and geothermal systems extend to 4–6 km, limited to the upper part of the Earth's crust. Magma feeding the current eruptions (and wider historic eruptions), mainly comes from the mid‐crust (5–7 km), though some comes from deeper (>15 km) beneath the base of the crust. Our results suggest this usually solid layer (the mantle) may be partially molten here. The Earth's crust gets thicker (from 15 to 20 km) moving eastwards along the Peninsula toward central Iceland. This likely reflects higher temperatures and more mantle material moving upwards allowing thicker crust to form as you go toward a large mantle upwelling, known as a mantle plume, thought to lie beneath central Iceland. Key Points A crustal‐scale regional shear‐wave velocity model of the Reykjanes Peninsula is derived from RFs and surface wave dispersion data Crustal thickness increases from 15 to 20 km eastwards toward the center of the Iceland Plume, due to increasing temperature/active upwelling Seismicity/geothermal regions are limited to the upper crust, magma is sourced from the lower crust, or a partially molten region sub‐Moho

Shale oil and gas exploitation by hydraulic fracturing experienced a strong development worldwide over the last years, accompanied by a substantial increase of related induced seismicity, either consequence of fracturing or wastewater injection. In Europe, unconventional hydrocarbon resources remain underdeveloped and their exploitation controversial. In UK, fracturing operations were stopped after the M w 2.3 Blackpool induced earthquake; in Poland, operations were halted in 2017 due to adverse oil market conditions. One of the last operated well at Wysin, Poland, was monitored independently in the framework of the EU project SHEER, through a multidisciplinary system including seismic, water and air quality monitoring. The hybrid seismic network combines surface mini-arrays, broadband and shallow borehole sensors. This paper summarizes the outcomes of the seismological analysis of these data. Shallow artificial seismic noise sources were detected and located at the wellhead active during the fracturing stages. Local microseismicity was also detected, located and characterised, culminating in two events of M w 1.0 and 0.5, occurring days after the stimulation in the vicinity of the operational well, but at very shallow depths. A sharp methane peak was detected ~19 hours after the M w 0.5 event. No correlation was observed between injected volumes, seismicity and groundwater parameters.

Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community . Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology .

Understanding the magnetic excitations in high-temperature (high- T c ) copper-oxide superconductors is important because they may mediate the electron pairing for superconductivity 1 , 2 . By determining the wavevector ( Q ) and energy (ħ ω ) dependence of the magnetic excitations, it is possible to calculate the change in the exchange energy available to the superconducting condensation energy 3 , 4 , 5 . For the high- T c superconductor YBa 2 Cu 3 O 6+ x , the most prominent feature in the magnetic excitations is the resonance 6 , 7 , 8 , 9 , 10 , 11 , 12 . Suggestions that the resonance contributes a major part of the superconducting condensation 4 , 13 have not gained acceptance because the resonance is only a small portion of the total magnetic scattering 12 , 13 , 14 . Here, we report an extensive mapping of magnetic excitations for YBa 2 Cu 3 O 6.95 ( T c ∼93 K). Absolute intensity measurements of the full spectra allow us to estimate the change in the magnetic exchange energy between the normal and superconducting states, which is about 15 times larger than the superconducting condensation energy 15 , 16 —more than enough to provide the driving force for high- T c superconductivity in YBa 2 Cu 3 O 6.95 .