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We apply rock mechanics concepts to the seismological observations in order to explain why during hydraulic injection some events display tensile and some shear deformation. The presence of non‐shear components depends on the differential stress and the fracture orientation with respect to the σ1 direction. Provided the slip vector is parallel to the traction we define four types of earthquakes according to the ratio of the shear and tensile components. Assuming a Griffith failure envelope, hybrid events containing both shear and tensile components can occur for fractures striking within 22.5° of σ1. We argue that pure tensile fractures striking parallel to σ1 are unlikely in the presence of natural fractures. The low shear traction of tensile events also implies their small stress drops. By applying the analysis to two different data sets, Soultz‐sous‐Forets and Cotton Valley, we show that different orientations of natural fractures and differential stress in the targeted formations made each region favorable for different non‐DC components in the injection‐induced seismicity.

Rapid population and economic growth have increased the demand for depleting resources. Nitrogen (N) and phosphorus (P) are mineral elements that perform important functions in plants, but their extraction is not sustainable. In addition, these elements contribute significantly to the eutrophication of water bodies. The recovery of these nutrients from wastewater by adsorption techniques offers a promising solution. Previous studies have demonstrated the adsorption capabilities of materials such as zeolite for ammonium (NH4+) and biochar for P. In addition, these materials can serve as a source of N and P for plants in a circular economy context. In this regard, this study aims to evaluate the recovery of N and P by the adsorption capacities of zeolite and biochar through a column test with treated wastewater. Two columns positioned in series, one filled with 2.7 kg of zeolite and the other with 397 g of biochar, were placed at the outlet of the full-scale sewage treatment plant of Marineo (Italy). The zeolite adsorbed 3.6 g of NH4+ accumulated during the test with a rate of adsorption of 44% and adsorption of 1.33 mg g−1 of NH4+. The biochar adsorbed about 11 g of P accumulated during the test, with an adsorption percentage of 13% and an adsorption of 26.75 mg g−1 of P. Despite some problems related to the effluent used during the test, the tested materials showed good adsorption properties.

The source scanning method allows for not only the automated determination of the earthquake locations but also the study of the earthquake source processes. It is based on shifting seismograms back in time by the travel times and capitalizes on summing them over the seismic stations. In this way, it produces a brightness field. Using the results from synthetic seismogram tests, we show that the vector from the hypocenter to the brightspot equals a vector of the unilateral earthquake rupture propagation. We apply source scanning to study rupturing of 12 natural West Bohemian (the Czech Republic, Central Europe) earthquakes in a magnitude range from 1.6 to 3.7 recorded by the WEBNET (up to 23 stations at epicentral distances of up to approximately 25 km). The travel times were calculated by the ray method and adjusted by adding the location arrival-time residuals. The normalized envelopes of the vertical component of the direct P wave velocity seismograms were used for source scanning. We estimated the rupture direction and identified which nodal plane was the fault plane from the brightness field for each of the earthquakes. The reliable outcomes of the rupture direction estimation had the rupture azimuth to be towards the north and the southeast. Upward rupturing was found for 11 earthquakes, whereas downward rupturing occurred in only 1 earthquake. The method is useful as an auxiliary method for fault plane identification.

Seismic coda represents a valuable source of information about the attenuation of the high-frequency waves in the studied region. The quality factor Q derived from coda is an integral parameter of the volume surrounding the hypocenter and seismic station and, according to the applied method, represents the total attenuation or the intrinsic and scattering parts. We analyzed records of 13 selected earthquakes in the magnitude range 1.7–2.9 of the 2011 swarm from West Bohemian/Vogtland area (central Europe), which were recorded at epicentral distances from 7 to 50 km. Two methods were applied: coda method for estimation of the Q c and the Multiple Lapse Time Windows Analysis for separation of the scattering and intrinsic loss by estimation of Q i and Q sc . Careful selection of the analyzed events was necessary due to the frequent contamination of coda decays by the running seismic swarm activity. The resulting coda Q c is relatively high with respect to the geodynamic activity and varies between 100 and 2500 within the analyzed frequency range of 1–18 Hz. The intrinsic loss dominates over scattering attenuation with Q i increasing from 100 and 1850 and Q sc from 300 to 3400 in the same frequency range, which is consistent with the geodynamic activity of the region. We find that the intrinsic attenuation in West-Bohemia/Vogtland is higher that in neighboring Germany, which could be attributed to the heterogeneity of the crust in central Europe.

The 2021 Fagradalsfjall eruption on Iceland’s Reykjanes Peninsula was preceded by an intense seismic swarm, offering an opportunity to investigate fluid dynamics and faulting processes at divergent plate boundary. Here we analysed 1306 full moment tensors of pre-eruption dike-related earthquakes and identified three faulting regimes: strike-slip, normal and reverse, driven by variations in vertical stress and controlled by fluid dynamics and crustal heterogeneity. Systematic volumetric components of these earthquakes revealed both tensile opening and compressive closing of cracks. Notably, crack closing dominated shallow, fractured crust, associated with surface subsidence above the dike, while crack opening occurred within the impermeable crust, suggesting overpressured fluids trapped at structural barriers. These variations highlight the role of fluid-rock interactions and anisotropic permeability in driving fault behaviour. Our results demonstrate that non-double-couple components of earthquakes are sensitive indicators of evolving stress and fluid migration. They provide insights into the mechanics of seismo-volcanic unrest at the slow-spreading rift. Seismic swarm before the 2021 Fagradalsfjall eruption reveals vertical stress changes and fluid-driven fracture processes linked to crustal heterogeneities, evidenced by moment tensor analysis of 1306 earthquakes exhibiting both crack opening and closure.

The Åknes rockslide in Western Norway is characterised by a steady movement of a rock mass with an extent of about 1 km2 and a yearly deformation rate in the range of 2 to 4 cm. A seismic network consisting of 8 three-component geophones records tens to hundreds of local and distant seismic events daily. Depending on their character, local seismic events show a variety of waveforms, both with abrupt and emergent onsets. Along with the relatively low frequencies of the waveforms, standard location procedure using arrival time measurements is difficult to apply. Based on the event envelopes, we classify local events and obtain their approximate location by stacking STA/LTA ratios of back-projected waveforms. To suppress the influence of complex surface morphology and related complicated wave propagation, we constrain hypocentres to the surface of the slope and determine only horizontal coordinates. The method was successfully tested by locating two types of ground truth data: calibration shots and a block collapse. The test proved the ability of the method to determine the position of sliding events with an uncertainty of less than 36 m, which allows to distinguish amongst several foci of rockslide activity. Application of the method to 8 years of monitoring data shows continuous seismic activity, which is concentrated in the centre and at the western edge of the monitored area. Most likely, microseismic events recorded by the seismic network originate within the body of the rock slope and are related to its disintegration or potentially to sliding on the detachment fault.

Soil and water pollution caused by excessive use of fertilizers and resource scarcity are critical issues in modern horticulture. Although laboratory tests are reliable, they take time and use chemical reagents that must be disposed of and complex protocols. Monitoring plant nutrient status through technologies that allow continuous and rapid assessment is crucial for precise resource management. Several proximal and remote sensors that use different physico-chemical principles to monitor plant nutrient status are available nowadays. However, these technologies still have important operative and structural limitations that must be overcome. The aim of this review is to summarize the current status and latest developments in proximal and remote sensors capable of monitoring plant and soil nutrients, focusing on sensor types, principles, applications, and their strengths and weaknesses. Electrochemical proximal sensors allow continuous monitoring of nutrients in the plant sap or in the soil solution but work on a single spot basis. Instruments based on optical sensors allow immediate measurements and quick analysis, but do not work on a continuous basis. On the other hand, remote sensors, such as drone-mounted cameras and satellite systems, are based on large-area imaging and can be used to estimate crop nutrient status by processing images at different wavelengths. Finally, combining proximal and remote techniques may be needed to achieve very accurate monitoring of plant and nutrient status.

A singular sequence of three episodes of ML3.5, 4.4 and 3.6 mainshock-aftershock occurred in the West Bohemia/Vogtland earthquake-swarm region during 2014. We analysed this activity using the WEBNET data and compared it with the swarms of 1997, 2000, 2008 and 2011 from the perspective of cumulative seismic moment, statistical characteristics, space-time distribution of events, and prevailing focal mechanisms. For this purpose, we improved the scaling relation between seismic moment M0 and local magnitude ML by WEBNET. The total seismic moment released during 2014 episodes (M0tot≈1.58×1015 Nm) corresponded to a single ML4.6+ event and was comparable to M0tot of the swarms of 2000, 2008 and 2011. We inferred that the ML4.8 earthquake is the maximum expected event in Nový Kostel (NK), the main focal zone. Despite the different character of the 2014 sequence and the earthquake swarms, the magnitude-frequency distributions (MFDs) show the b-values ≈ 1 and probability density functions (PDFs) of the interevent times indicate the similar event rate of the individual swarms and 2014 activity. Only the a-value (event-productivity) in the MFD of the 2014 sequence is significantly lower than those of the swarms. A notable finding is a significant acceleration of the seismic moment release in each subsequent activity starting from the 2000 swarm to the 2014 sequence, which may indicate an alteration from the swarm-like to the mainshocks-aftershock character of the seismicity. The three mainshocks are located on a newly activated fault segment/asperity (D in out notation) of the NK zone situated in the transition area among fault segments A, B, C, which hosted the 2000, 2008 and 2011 swarms. The segment D appears to be predisposed to an oblique-thrust faulting while strike-slip faulting is typical of segments A, B and C. In conclusion, we propose a basic segment scheme of the NK zone which should be improved gradually.

The relative locations of earthquake hypocentres determined with the master-event (ME) or the double-difference (DD) methods are more accurate and less dispersive compared to the absolute locations. In this paper, we conduct synthetic tests to assess the accuracy of the ME and DD location methods, to study the effects of the control parameters on the locations and possible distortions of the foci geometry. The results indicate that the DD locations are, in general, more accurate than the ME locations and perform significantly better for large earthquake clusters due to their independence of the master event position. The location precision, however, strongly depends on the control parameters used. If the control parameters are optimally chosen, the location errors can be considerably reduced. Moreover, it is proved that no distortion such as artificial clustering of foci is introduced if relative locations are used. Finally, the efficiency of both location methods is exemplified on locations of swarm micro-earthquakes that occurred in the West Bohemia region, Czech Republic, in order to reveal a detailed geometry of the active fault zone.

Mofettes are gas emission sites where high concentrations of CO2 ascend through conduits from as deep as the mantle to the Earth’s surface and as such provide direct windows to processes at depth. The Hartoušov mofette, located at the western margin of the Eger Graben, is a key site to study interactions between fluids and swarm earthquakes. The mofette field (10 mofettes within an area of 100 m × 500 m and three wells of 28, 108, and 239 m depth) is characterized by high CO2 emission rates (up to 100 t/d) and helium signatures with (3He/4He)c up to 5.8 Ra, indicating mantle origin. We compiled geological, geophysical, geochemical, and isotopic data to describe the mofette system. Fluids in the Cheb basin are mixtures between shallow groundwater and brine (>40 g/L at a depth of 235 m) located at the deepest parts of the basin fillings. Overpressured CO2-rich mineral waters are trapped below the mudstones and clays of the sealing Cypris formation. Drilling through this sealing layer led to blow-outs in different compartments of the basin. Pressure transients were observed related to natural disturbances as well as human activities. External (rain) and internal (earthquakes) events can cause pressure transients in the fluid system within hours or several days, lasting from days to years and leading to changes in gas flux rates. The 2014 earthquake swarm triggered an estimated excess release of 175,000 tons of CO2 during the following four years. Pressure oscillations were observed at a wellhead lasting 24 h with increasing amplitudes (from 10 to 40 kPa) and increasing frequencies reaching five cycles per hour. These oscillations are described for the first time as a potential natural analog to a two-phase pipe–relief valve system known from industrial applications.