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To what extent mechanical anisotropy is required to explain the dynamics of the lithosphere is an important yet unresolved question. If anisotropy affects stress and deformation, and hence processes such as fault loading, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with linear anisotropic viscosity can lead to deviatoric stress heterogeneity, strain-rate enhancement, as well as non-coaxial principal stress and strain rate. We develop an open-source finite-element software based on FEniCS for more complicated scenarios in both 2-D and 3-D. Mechanics of shear zones with transversely isotropic and orthorhombic anisotropy subjected to misoriented shortening and simple shearing are explored. A simple regional example for potential non-coaxiality for the Leech River Schist above the Cascadia subduction zone is presented. Our findings and these tools may help to better understand, detect and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation through fault loading. [ABSTRACT FROM AUTHOR]

This study investigates the use of calcium-based slurry for simultaneous removal NO and SO2 from oxy-fuel combustion flue gas, and recovery of the sulfur and nitrogen species in resulting solutions. The experiments were performed in a bubbling reactor in a transient mode under the pressure of 20 bar. The various influencing factors including the CaO amount, carrier gas (N2/CO2), and absorption time on the simultaneous NO and SO2 removal process, and the solution products were studied comprehensively. The results show that the NO2 removal efficiency can be improved by the presence of CO2, and the gas phase HNO2 produces in this process. The addition of CaO has positive effects not only on the NO2 removal efficiency but also on the formation of stable HNO3. With the presence of CO2, CaCO3 is formed in a solution initially. With the decrease of pH, CaCO3 is gradually converted to CaSO4, and in particular CaCO3 can be fully avoided through decreasing the pH of an absorption solution to 1.14. At the same time, the formation of unstable S(IV) and NO2- can be prevented when the solution pH is lower than 1.37. The nitrogen and sulfur compounds in the absorption solution (at pH 1.14) were further separated by the addition of different amounts of CaO. In particular, 95% of SO42- finally can be recovered in the form of CaSO4.2H2O with nitrogen in solution existing as NO3- by controlling the Ca/S ratio at 4.70. The effectiveness of calcium-based slurry on the removal and recovery of SO2 and NO is confirmed.

A bubbling reactor is an important type of gas scrubber to reduce SO2 emissions in maritime shipping. Both experiments and simulations were conducted to study the relationship between the periodic gas bubbling process and SO2 concentration at the outlet of the reactor, and the entrainment of liquid droplets on SO2 absorption. The accuracy of the model was verified by comparing the bubble size, the depth of bubbles injected into the water, and the SO2 concentration obtained in both experiments and simulations. The gas bubbling process is accompanied by bubble formation, rise, and collapse. The gas bubbling period is affected by the disturbance of the liquid level. The period of the SO2 concentration at the outlet of the gas bubbling reactor is smaller than that at the gas jar outlet which acts as the gas buffering region. The amounts of water carried out of the bubbling reactor by the gas bubbling process increase with the gas flow rates. The droplets and liquid film in the gas jar and the connecting tube play an important role in the absorption of SO2. This study encourages more research to reduce the fluctuation of SO2 concentration and consider droplet entrainment in the design of bubbling reactors. [ABSTRACT FROM AUTHOR]

Seismologic studies have reported seismic velocities reduction and Vp/Vs ratio changes over damage zones associated with seismogenic faults. The structure and elastic properties of these damage zones indicate the maturity of faults and affect the rupture dynamics of future seismic events. Therefore, they contain critical information about fault properties that could inform seismic hazards. Here we present a geodetic modeling approach to constrain velocity changes and elastic properties of fault damage zones under stress perturbation from nearby earthquakes. Compared to seismic tomographic analysis that is usually limited by resolution, this geodetic approach provides tighter constraints on the elastic properties and geometry of the damage zone at shallow depths. Our results imply that a major component of the shallow strain release is distributed and inelastic. The existence of numerous shallow faults either may indicate a locally detached shallow layer or they are remnants from earlier fault evolution. Plain Language Summary: Ruptures of large earthquakes tend to fracture the materials nearby, thus creating a zone with lower seismic velocity, which is known as fault damage zone. Understanding the structure and mechanics of this zone will help reveal the status of fault evolution and seismogenic depth for future ruptures. To achieve that, we developed a geodetic modeling approach to determine the geometric and physical parameters of fault damage zones, utilizing observations from high‐resolution Interferometric Synthetic Aperture Radar and strain release estimates from kinematic fault slip models. By searching the parameters in a specific order, each unknown could be uniquely constrained from the observed deformation profiles. The approach works well with fault damage zones under compliant motion induced by the stress from nearby earthquakes. The method is straightforward, computationally efficient and is applicable even to a fault damage zone with 250 m width near the 2019 Ridgecrest earthquake sequence. Our study suggests that these structures are quite shallow and accommodate a major component of shallow strain release. Key Points: We developed a geodetic modeling approach to constrain structural and mechanical properties of fault damage zonesThe approach is straightforward, computationally efficient, and works well even over a small fault damage zone with 250 m widthThe existence of many shallow fractures indicates distributed shallow strain release over transtensional shear zones [ABSTRACT FROM AUTHOR]

Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self‐consistent, physics‐based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three‐dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary‐element, finite‐element, and finite‐difference methods, in a community initiative. Our benchmarks consider a planar vertical strike‐slip fault obeying a rate‐ and state‐dependent friction law, in a 3D homogeneous, linear elastic whole‐space or half‐space, where spontaneous earthquakes and slow slip arise due to tectonic‐like loading. We use a suite of quasi‐dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain‐size‐dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community‐based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics. Plain Language Summary: Earthquakes and fault zone processes occur over time scales ranging from milliseconds to millennia and longer. Computational models are increasingly used to simulate sequences of earthquakes and aseismic slip (SEAS). These simulations can be connected to diverse geophysical observations, offering insights into earthquake system dynamics. To improve these simulations, we pursue community efforts to design benchmarks for 3D SEAS problems. We involve earthquake researchers around the globe to compare simulation results using different numerical codes. We identify major factors that contribute to the discrepancies among simulations. For example, the spatial dimension and resolution of the computational model can affect how earthquakes start and grow, as well as how frequently they recur. Code comparisons are more challenging when we consider the Earth's surface in the simulations. Fortunately, we find that several key characteristics of earthquakes are accurately reproduced in simulations, such as the duration, total movement, maximum speed, and stress change on the fault, even when model resolutions are not ideal. These exercises are important for promoting a new generation of advanced models for earthquakes. Understanding the sensitivity of simulation outputs will help test models against real‐world observations. Our community efforts can serve as a useful example to other geoscience communities. Key Points: We pursue community efforts to develop code verification benchmarks for three‐dimensional earthquake rupture and crustal faulting problemsWe assess the agreement and discrepancies of seismic and aseismic fault behavior among simulations based on different numerical methodsOur comparisons lend confidence to numerical codes and reveal sensitivities of model observables to major computational and physical factors [ABSTRACT FROM AUTHOR]

Understanding mechanical conditions that lead to complexity in earthquakes is important to seismic hazard analysis. In this study, we simulate physics‐based multicycle dynamic models of the San Andreas fault (Carrizo through San Bernardino sections) and the San Jacinto fault (Claremont and Clark strands). We focus on a complex fault geometry based on the Southern California Earthquake Center Community Fault Model and its effect over multiple earthquake cycles. Using geodetically derived strain rates, we validate the models against geologic slip rates and recurrence intervals at various paleoseismic sites. We find that the interactions among fault geometry, dynamic rupture and interseismic stress accumulation produce stress heterogeneities, leading to rupture segmentation and variability in earthquake recurrence. Our models produce earthquakes with rupture extents similar to a recent comprehensive paleoseismic catalog. The "earthquake gates" of the Big Bend and the Cajon Pass occasionally impede dynamic ruptures. The angle of compression, which is the subtraction of the maximum shear strain rate direction from the local fault strike, can better determine the likelihood of the impedance of restraining bends to dynamic ruptures. Because the Big Bend has an angle of compression of ∼20°, ruptures that traverse the Big Bend, like the 1857 Fort Tejon earthquake, are more frequent than expected based on empirical relations which predict the ∼40° restraining bend to terminate most ruptures. Our models indicate that large ruptures tend to initiate north of the Big Bend and propagate southwards, similar to the 1857 earthquake, providing critical information for ground shaking assessment in the region. Plain Language Summary: The historical and prehistoric earthquake record from the southern San Andreas and San Jacinto faults contains ruptures that have both variable lengths and recurrence times. Understanding the causes behind the complexity would advance our knowledge of earthquake dynamics and could improve earthquake forecasts. To achieve this, we need numerical models to integrate various datasets from geodesy, structural geology, seismology, and paleoseismology. In this study, we simulate earthquake cycles using a complex 2D fault geometry. We find that fault geometry interacts with other mechanical factors to produce heterogeneous stresses, leading to simulated earthquakes with various rupture extents and irregular return times that mimic quakes known from the geologic record. In our model we find that the Big Bend on the San Andreas fault controls rupture extent and large ruptures tend to initiate north of the Big Bend and propagate southwards, similar to the 1857 Fort Tejon earthquake. Continued research is needed to understand rupture extent variability near Cajon Pass and we identify promising research possibilities. Key Points: Multicycle dynamic models with realistic 2D fault geometry of the southern San Andreas and the northern San Jacinto faults are simulatedStress heterogeneity from interactions between fault geometry and dynamic ruptures produces diverse rupture extent and recurrenceLarge ruptures tend to initiate north of the Big Bend and propagate southwards, similar to the 1857 Fort Tejon earthquake [ABSTRACT FROM AUTHOR]

Coal-based mercury pollution from power plants has received increasing attention. In a previous study, high iron and calcium coal ash (HICCA) was found as a promising oxygen carrier (OC) for chemical looping combustion (CLC). The purpose of this study was to investigate the catalytic effect of HICCA on Hg0 removal as well as the impacts of several gas impurities, such as HCl, SO2, and NO. Experiments on Hg0 removal efficiencies for different atmospheres were performed in the fixed-bed reactor at 850 °C. Based upon the characterization of BET, SEM, XRD, XPS, and EDS of reaction products, the reaction mechanisms of different gases with the HICCA samples were established. The mechanisms were further explained using the thermodynamic equilibrium calculations. The experimental results showed that the Hg0 removal efficiency using HICCA was 11.60%, while the corresponding value in the presence of 50 ppm HCl was 90.46%. Hg0 removal by HICCA involving HCl is mainly attributed to homogeneous reaction between Hg0 and HCl as well as the formation of reactive species (Cl, Cl2, Cl2O, O, S, and SCl2) through the reactions of HCl with Fe2O3 and CaSO4 in HICCA. The formation of C–Cl bond is not the main pathway for the promotional effect of HCl on Hg0 removal. SO2 played a negative role in Hg0 removal by HICCA. The inhibition of SO2 may be attributed to its effect on the reduction of Fe2O3 and its bonding with C–O, COOH, and C(O)–O–C. NO enhanced Hg0 removal by HICCA primarily through the homogeneous reactions of Hg0 with N2O and O. In addition, NO also interacted with HICCA and promoted the heterogeneous oxidation of Hg0 by producing more C–O, C=O, and COOH/C(O)−O−C on HICCA surface. This study proved the effectiveness of HICCA on Hg0 removal in iG-CLC and revealed the mechanisms of the interaction between HCl/SO2/NO and MxOy/CaSO4 as well as carbon-oxygen groups. [ABSTRACT FROM AUTHOR]

To solve the ash deposition problem caused by burning high‐calcium Zhundong coal (ZDC), the addition of vermiculite is a promising solution. However, complete mechanisms of vermiculite addition reducing ash deposition are still unknown. In this paper, the effect of vermiculite on sodium emission, ash fusion characteristics, and mineral transformation is investigated. The results show that although vermiculite, with limited Na capture capacity, lowers the ash fusion temperatures (AFTs), it can greatly reduce ash deposition. In the combustion of ZDC, calcium‐bearing minerals will react with clay minerals and then convert to molten glassy phase. Those molten minerals will take high melting point minerals, Ca2Al2SiO7 and CaMgSi2O6, as bone, showing slagging phenomenon with high AFTs. When vermiculite is introduced, the main reaction products are Ca2MgSi2O7 and Mg2SiO4 and that reduces the extent of molten minerals formation. The main ash product transforming from Ca2Al2SiO7 to Ca2MgSi2O7 leads to the decrease of AFTs. The initial ash deposition with Ca2Al2SiO7 still happens; however, vermiculite addition makes it hard for ash to grow on the existing ash deposit. The results of FactSage software agree with the experimental ones, and the proportion of slag decreases by 36% with vermiculite at 1250°C. [ABSTRACT FROM AUTHOR]

We develop a finite element dynamic earthquake simulator, EQsimu, to model multicycle dynamics of 3-D geometrically complex faults. The fault is governed by rate- and state-dependent friction (RSF). EQsimu integrates an existing finite element code EQdyna for the coseismic dynamic rupture phase and a newly developed finite element code EQquasi for the quasi-static phases of an earthquake cycle, including nucleation, post-seismic and interseismic processes. Both finite element codes are parallelized through Message Passing Interface to improve computational efficiency and capability. EQdyna and EQquasi are coupled through on-fault physical quantities of shear and normal stresses, slip-rates and state variables in RSF. The two-code scheme shows advantages in reconciling the computational challenges from different phases of an earthquake cycle, which include (1) handling time-steps ranging from hundredths of a second to a fraction of a year based on a variable time-stepping scheme, (2) using element size small enough to resolve the cohesive zone at rupture fronts of dynamic ruptures and (3) solving the system of equations built up by millions of hexahedral elements. EQsimu is used to model multicycle dynamics of a 3-D strike-slip fault with a bend. Complex earthquake event patterns spontaneously emerge in the simulation, and the fault demonstrates two phases in its evolution. In the first phase, there are three types of dynamic ruptures: ruptures breaking the whole fault from left to right, ruptures being halted by the bend, and ruptures breaking the whole fault from right to left. As the fault bend experiences more ruptures, the zone of stress heterogeneity near the bend widens and the earthquake sequence enters the second phase showing only repeated ruptures that break the whole fault from left to right. The two-phase behaviours of this bent fault system suggest that a 10° bend may conditionally stop dynamic ruptures at the early stage of a fault system evolution and will eventually not be able to stop ruptures as the fault system evolves. The nucleation patches are close to the velocity strengthening region. Their sizes on the two fault segments are different due to different levels of the normal stress. [ABSTRACT FROM AUTHOR]

Mud volcanoes are significant indicators of neotectonic activity and have important research significance. Mud volcanoes can not only be used as an important index for the long‐term evaluation of oil and gas fields but are also an important symbol for locating gas hydrates in the seabed. Additionally, the eruption of mud volcanoes will affect drilling, pipe laying, and other projects, and the eruption of large amounts of methane gas can also cause greenhouse effects and climate change. The trigger mechanisms of mud volcanoes have always been a focus of debate among geologists. In recent years, many scholars have argued that mud volcanoes are triggered by earthquake activity. However, the stress and strain caused by earthquakes and their control mechanisms on the eruption of mud volcanoes still require further study. This paper is based on the calculated results of static stresses caused by the M5.5 Wusu earthquake of May 2, 1995, the M5.4 Shawan earthquake of January 9, 1996, the M5.3 Shihezi earthquake of February 14, 2003, and the M6.3 Xinyuan–Hejing earthquake of June 30, 2012, on the Horgos, Dushanzi, Aiqigou, and Baiyanggou mud volcanoes distributed in the southern margin of the Junggar Basin, NW China. The calculated static stresses, the earthquake response characteristics of these four groups of mud volcanoes, and the continuous observational data of the Horgos mud volcanoes showed that static stresses from these earthquakes did not reach the triggering threshold, though the mud volcanoes exhibited a good relationship with earthquakes. We speculate that static stress may not be the main triggering mechanism for the mud volcanoes and that the mechanisms of earthquake triggering may be divided into two types: (a) For a mud volcano in a critical state before an earthquake, dynamic stress changes may trigger eruption of the mud volcano by increasing permeability and mobilizing magma; (b) for mud volcanoes that have not yet reached the critical eruption state before an earthquake, both static and dynamic stresses play roles in their activities. [ABSTRACT FROM AUTHOR]

The removal of ibuprofen (IBP) from wastewater is a hot topic in both academic and industrial fields. Herein, we reported a novel eco-friendly absorbent C3N4/soot composite via a simple one-step pyrolysis process, which had high adsorptive activity for the removal of IBP from wastewater. Adsorption kinetic and isotherm data of the adsorption process were investigated. The adsorption capacity at room temperature for low equilibrium concentration (10 mg/L) was as high as 104 mg/g, which was very similar to the maximum adsorption capacity (148.81 mg/g). The pseudo-first-order, pseudo-second-order, and the intraparticle diffusion models could best describe adsorption kinetics of IBP on 7 wt% C3N4/soot, and adsorption isotherm is well fitted to Langmuir model. Thermodynamic parameters (ΔH, ΔG, and ΔS) indicated that IBP adsorption on C3N4/soot composite was spontaneous and endothermic. Moreover, the potential adsorption mechanism of C3N4/soot composite for the adsorption of IBP was proposed. The 7 wt% C3N4/soot composite exhibited much higher adsorptive activity and still showed a relatively high adsorption stability even after five cycles, which were potentially suitable for high efficiency and low-cost water purification. [ABSTRACT FROM AUTHOR]

Four-wall tangential firing (FWTF) is a newly developed furnace arrangement used in supercritical and ultra-supercritical 600-MW boilers. In this study, flow characteristics of the flue gas in furnace of a 660-MW boiler firing pulverized coal with FWTF arrangement were investigated through numerical simulations. The variation characteristics of the tangential circle size of the furnace and flue gas bias at the furnace exit were determined. The results show some differences in the flue gas characteristics between the FWTF and traditional four-corner tangential firing (FCTF) in the furnace. In the FWTF, the variation in the actual sizes of the tangential circle in the burner zone is insignificant; the maximum size with respect to geometric limitations is largely maintained. Hence, unlike conventional FCTF, the size of the tangential circle cannot be used as a reliable parameter to analyze the variation in flue gas characteristics in the FWTF. Moreover, the flue gases are uniform and have high filling factors in the furnace. The simulation results show that, in the FWTF, the residual rotational momentum near the furnace exit is significant, thereby leading to variations in the flow and temperature on both sides of the furnace exit. This behavior is similar to that observed in the FCTF, which requires sufficient attention. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Experiments in a well-stirred reactor show three pH regions of SO2 absorption. [•] The operational pH of sodium quench units is recommended to be in region 2. [•] Operating in region 2 achieves a high absorption rate and low sodium loss. [•] The operational window narrows with the increase of sodium solution concentrations. [•] The operational window narrows at low partial pressure of SO2. [Copyright &y& Elsevier]

Abstract: Oxy-fuel combustion is an emerging technology to mitigate CO2 emissions from power plants. Compared with other CO2 capture technologies, gas impurities in oxy-fuel flue gas are highly concentrated, among which SO2 is of concern. Dynamic transient experiments have been conducted in a semi-batch well stirred reactor (WSR) relevant to the conditions of the flue gas scrubbers operating at atmospheric pressure prior to CO2 compression in oxyfuel technology for CCS. SO2 in N2 as well as in CO2 were considered. The initial pH of the solutions considered was those of NaOH (with concentrations of 0.01M and 1M), Na2CO3 (0.005M) and NaHCO3 (0.01M). Analysis of the liquid solutions showed that the concentration of bicarbonate increases with pH at a pH larger than 5.5 indicating a loss of effectiveness of the sodium reagent. A practical discharge pH of the liquid discharge from the scrubber is also greater than 4 as at a lower pH the absorption rate of SO2 reduced. This operating range is consistent with the reported operating range of the scrubber used in the Vattenfall oxyfuel pilot plant. [Copyright &y& Elsevier]

Liquid‐phase mass transfer coefficient is important for characterization of gas–liquid reactors and relevant to the modelling of gas absorption rate. Both direct and indirect methods have been used to obtain this coefficient. However, these methods have not been compared on the same basis. Liquid‐phase mass transfer coefficients were measured in three ways—(a) CO2 absorption into water, (b) SO2 absorption into 1 kmol m−3 of HCl, and (c) O2 absorption into Na2SO3—and then normalized to the coefficient for SO2. Based on transient experiments, the normalized values for liquid‐phase mass transfer coefficient obtained from three methods are in turn of kL,O2>kL,SO2>kL,CO2. The fluxes of SO2 predicted from three methods were further compared with the experimental values measured in SO2‐NaOH system. The fluxes predicted from kL,SO2 agreed well with the experimental values, whereas those from kL,CO2 and kL,O2 were significantly lower or higher. Therefore, the liquid‐phase mass transfer coefficient is preferably obtained from the targeted gas. Modelling on the flux of SO2 demonstrates the transition of controlling regions against pH. At pH above 4, the gas side resistance is larger than the liquid side, whereas at pH below 4, the gas side resistance is smaller than the liquid side. [ABSTRACT FROM AUTHOR]