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The quadratic Wasserstein (W2) metric has been proposed as a promising misfit function to mitigate cycle‐skipping phenomena in full‐waveform inversion. Mathematically, we demonstrate that the smoothness of the W2‐based adjoint source is two orders of magnitude higher than that based on L2‐norm, which guarantees a larger convergence radius of related inverse problems. However, the oscillatory characteristics of seismic signals and subsequent operations of transforming them into probability densities would decrease the accuracy of the optimal transport map T(t) and exacerbate the nonconvexity of the misfit function. To tackle these challenges, we propose the concept of prescribed direction indicator, which indicates the properly matching direction from predictions to observations, in order to correct inaccurate T(t). 1D synthetic examples suggest that reasonable bijection can be constructed through the proposed method. Numerical experiments demonstrate that it works well during optimization procedures, including enlarging the convergence radius of the inverse problem, improving the computational efficiency and enhancing the reliability of inversion results. Plain Language Summary: Full waveform inversion serves as a powerful tool to enhancing our understanding of Earth's interior structure. However, the traditional L2‐norm‐based method often falls into a local minimum due to the well known cycle‐skipping problem. To address this issue, a novel technique named the Quadratic Wasserstein Metric has been proposed, which yields smoother and more reliable results. Nevertheless, a challenge persists regarding the low precision in calculating the optimal transport map. To counteract this problem, we have introduced a tool called the "Prescribed Direction Indicator," which allows us to correct our calculations of the transport map and assist us in identifying the appropriate alignment between predictions and observations. With numerical synthetic experiments, we prove its superiority to the traditional Wasserstein metric in handling seismic inversions across a variety of scales, from small and local to global problems. Key Points: We mathematically prove W2‐based adjoint source's smoothness is two orders higher than L2‐basedWe propose a concept of prescribed direction indicator to correct inaccurate optimal transport map T(t)Numerical experiments demonstrate the superiority of our proposed method compared to the traditional W2 metric [ABSTRACT FROM AUTHOR]

Over the past decade, the seismicity rate in the state of Oklahoma has increased significantly, which has been linked to industrial operations, such as saltwater injection and hydraulic fracturing. Taking advantage of induced earthquakes and recently deployed seismometers, we construct a 3‐D radially anisotropic seismic velocity model for the crust of Oklahoma by using full waveform inversion. To mitigate the well‐known cycle‐skipping problem, we use misfit functions based on phase and waveform differences in several frequency bands. Relative velocity perturbations in the inverted model allow us to delineate major geological provinces in Oklahoma, such as the Anadarko Basin and the Cherokee Platform/Shelf. In addition, radial anisotropy in the inverted model reflects deformation within the crust of Oklahoma, which might correlate with sedimentary layering, microcracks/fractures, as well as dominant orientation of anisotropic minerals. The crystalline basement beneath Oklahoma can be inferred from the new velocity model, which enables us to better classify induced seismicity in current earthquake catalogs. Furthermore, synthetic experiments suggest that the new velocity model enables us to better constrain earthquake locations in Oklahoma, especially for determining their depths, which are important for investigating induced seismicity. Plain Language Summary: Taking advantage of induced earthquakes and seismometers deployed in Oklahoma in the last decade, we construct a radially anisotropic seismic velocity model for the crust beneath Oklahoma by using full waveform inversion. The data misfit is iteratively reduced by about 40%, and predicted seismograms based on the new velocity model can fit observations very well. We can identify geological structures from the velocity model, such as low velocity anomalies associated with the Anadarko Basin, and fast anomalies related to the Cherokee Platform. Positive radial anisotropy (RA) in the shallow crust might reflect layered sedimentary structure, while negative RA within the middle crust may relate to preferred orientation of anisotropic minerals, such as plagioclase, mica, and amphibole. Furthermore, synthetic tests are used to illustrate the impact of lateral variations of seismic velocity on earthquake locations, especially for focal depths. Therefore, this new 3‐D model provides us an opportunity to improve current earthquake catalogs in Oklahoma, as well as improving our understanding of the triggering mechanisms of induced earthquakes. Key Points: We use full waveform inversion to construct a 3‐D radially anisotropic seismic velocity model for the crust of OklahomaSpatial distributions of inverted velocity and radial anisotropy agree with geological provinces and tectonic deformation in OklahomaLateral velocity heterogeneities have strong impact on earthquake locations, especially for focal depths [ABSTRACT FROM AUTHOR]

Different bimetallic platinum and bismuth catalysts supported on melamine‐modified activated carbon (AC) are designed by a co‐impregnation method. Through controlling the activation temperatures of the melamine−AC mixture, a series of N‐doped and C3N4‐modified AC (N−AC and C3N4−AC) are prepared. Combined powder X‐ray diffractions, X‐ray photoelectron spectroscopic, and high‐angle annual dark‐field scanning transmission electron microscopic studies demonstrate that the introduction of C3N4 favors the formation of PtBi alloy and leads to increased particle sizes in comparison to the pristine and N‐doped AC‐supported bimetallics. The catalytic performance of the developed catalysts is evaluated in the oxidation of n‐heptanol oxidation in a batch mode using O2 as the oxidant. PtBi/C3N4−AC exhibits significantly boosted activity as well as selectivity to heptanoic acid as compared with the other catalysts. A high yield of heptanoic acid of 69 % can be achieved under the optimized reaction conditions. Furthermore, our work points to the PtBi alloy as the most active sites for the alcohol oxidation. Catalyst deactivation occurs in the cycling tests, mainly due to the collapse of the alloy phase and likely the decrease in particle sizes. [ABSTRACT FROM AUTHOR]

Significant imbalances in terrestrial water storage (TWS) and severe drought have been observed around the world as a consequence of climate changes. Improving our ability to monitor TWS and drought is critical for water‐resource management and water‐deficit estimation. We use continuous seismic ambient noise to monitor temporal evolution of near‐surface seismic velocity, dv/v, in central Oklahoma from 2013 to 2022. The derived dv/v is found to be negatively correlated with gravitational measurements and groundwater depths, showing the impact of groundwater storage on seismic velocities. The hydrological effects involving droughts and recharge of groundwater occur on a multi‐year time scale and dominate the overall derived velocity changes. The thermoelastic response to atmospheric temperature variations occurs primarily on a yearly timescale and dominates the superposed seasonal velocity changes in this study. The occurrences of droughts appear simultaneously with local peaks of dv/v, demonstrating the sensitivity of near‐surface seismic velocities to droughts. Plain Language Summary: Terrestrial water storage (TWS) is fundamental to the well‐being of inhabitants on Earth. However, current approaches to measure TWS variations have limited temporal or spatial resolution. In this study, we use near‐surface seismic velocity variations, dv/v, derived from continuous seismic recordings to monitor changes of TWS in central Oklahoma. A negative correlation between the long‐term trend of dv/v with gravity measurements reflects the impact of groundwater recharge/discharge on near‐surface seismic velocity. In addition, a seasonal cycling of dv/v has similar periodicity to recordings of air temperature, which can be explained by thermo‐elastic strain at the subsurface. Comparisons between dv/v and drought index further show the possibility of using near‐surface seismic velocity as a proxy for monitoring severe drought for local communities. Considering the high temporal sampling and flexible spatial deployment, seismometers may be used to monitor subsurface water distributions. This can be useful for sustainable water management and reliable water‐deficit estimation. Key Points: A long‐term trend of dv/v in Oklahoma correlates well with gravity measurements, which may reflect groundwater recharge and dischargeShort‐term peaks of dv/v agree with the drought index, demonstrating a potential for monitoring meteorological droughtsA seasonal cycle of dv/v in central Oklahoma can be explained by thermo‐elastic strains driven by atmospheric temperature changes [ABSTRACT FROM AUTHOR]

One important feature of the Greenland Ice Sheet (GrIS) change is its strong seasonal fluctuation. Taking advantage of deployed seismographic stations in Greenland, we apply cross‐component auto‐correlation of seismic ambient noise to measure in‐situ near surface relative velocity change (dv/v) in different regions of Greenland. Our results demonstrate that dv/v measurements for most stations have less than 3 months lag times in comparison to the surface mass change. These various lag times may provide us constraints for the thickness of the subglacial till layer over different regions in Greenland. Moreover, in southwest Greenland, we observe a change in the long‐term trend of dv/v for three stations, which might be consistent with the mass change rate (dM/dt) due to the "2012–2013 warm‐cold transition." These observations suggest that seismic noise auto‐correlation technique may be used to monitor both seasonal and long‐term changes of the GrIS. Plain Language Summary: The changes of the Greenland Ice Sheet (GrIS) have important implications for both scientific research and human society. Due to its large size, the change of the GrIS varies at different regions. Here, we apply a seismic monitoring technique to study the GrIS mass change by using seismographic stations deployed in Greenland. The advantage of using this technique is that we are able to monitor different locations in a relatively simple, low‐cost and in‐situ way, and obtain indicative information about the ice mass change over time. We specify the seasonal fluctuations of seismic signals and connect them with the subglacial setting at different regions in Greenland, and explore the potential of using these seismic techniques to monitor the long‐term changes of the GrIS. Key Points: The seasonal variations of relative velocity change (dv/v) have <3 months lag with respect to the surface Greenland Ice Sheet (GrIS) changeLarger lag times of dv/v may provide constrains for thicker subglacial till layers in the central Greenlanddv/v may be used for monitoring long‐term GrIS mass change [ABSTRACT FROM AUTHOR]

By fitting observed data with predicted seismograms, least‐squares migration (LSM) computes a generalized inverse for a subsurface reflectivity model, which can improve image resolution and reduce artifacts caused by incomplete acquisition. However, the large computational cost of LSM required for simulations and migrations limits its wide applications for large‐scale imaging problems. Using point‐spread function (PSF) deconvolution, we present an efficient and stable high‐resolution imaging method. The PSFs are first computed on a coarse grid using local ray‐based Gaussian beam Born modeling and migration. Then, we interpolate the PSFs onto a fine‐image grid and apply a high‐dimensional Gaussian function to attenuate artifacts far away from the PSF centers. With 2D/3D partition of unity, we decompose the traditional adjoint migration results into local images with the same window size as the PSFs. Then, these local images are deconvolved by the PSFs in the wavenumber domain to reduce the effects of the band‐limited source function and compensate for irregular subsurface illumination. The final assembled image is obtained by applying the inverse of the partitions for the deconvolved local images. Numerical examples for both synthetic and field data demonstrate that the proposed PSF deconvolution can significantly improve image resolution and amplitudes for deep structures, while not being sensitive to velocity errors as the data‐domain LSM. Plain Language Summary: Seismic imaging is an important tool to detect hydrocarbon resource and study deep Earth's structure. Traditional ray‐based and wave equation imaging methods commonly extrapolate observed data and apply appropriate imaging condition to construct subsurface impedance interfaces. Mathematically, these methods can be considered as adjoint operators of seismic modeling, but they have difficulty to produce high‐quality images of complicated subsurface structures. To mitigate this issue, we present an efficient and stable high‐resolution imaging approach, i.e., the point‐spread function (PSF) deconvolution. The locally temporal and spatial limitations are utilized to efficiently compute the PSFs on a coarse grid using a ray‐based Gaussian beam propagator. Then, an on‐the‐fly interpolation on a fine grid and a wavenumber‐domain deconvolution are applied to improve image resolution. Numerical experiments for benchmark model and field data demonstrate the feasibility and adaptability of the proposed method for imaging complicated salt structure and low‐signal‐to‐noise data. Key Points: Conventional least‐squares migration is too expensive to be widely applied for large‐scale problems under current computational capacityAn efficient approach for calculating point‐spread functions using local modeling and migration is proposedThe point‐spread function deconvolution is then applied to incorporate the Hessian effect and improve image quality [ABSTRACT FROM AUTHOR]

Ray theory gives a high‐frequency asymptotic solution of the wave equation, which has been widely used in the seismic study because of its high computational efficiency and good physical insights for elementary waves. However, the fundamental high‐frequency assumption makes it difficult to accurately simulate the finite‐frequency effect of wave propagations. On the other hand, the Gaussian beam, as one of the advanced ray‐based methods, overcomes the amplitude singularity problem near the caustics by introducing a complex‐valued paraxial approximation. But Gaussian beams only use the velocity and up to second‐order velocity derivative of central rays and thus does not accurately simulate the response of heterogeneity away from the rays. To bridge the gap between the ray theory and wave‐equation methods, we present a two‐way beam wave method and apply it to seismic imaging. A fan of central rays are first shot to extract local ray‐centered model parameters in the global Cartesian coordinates. Then, a finite‐difference method is used to solve the acoustic wave equation in the ray‐centered coordinates to simulate wave propagations near the central rays. The beam wave method can accurately simulate the response of the velocity heterogeneities in the ray tubes and therefore produces more accurate wavefields. In addition, we discretize the ray‐centered wave equation onto a non‐orthogonal grid, which considerably reduces the computational cost. We apply the two‐way beam wave method in seismic imaging and develop a beam wave reverse‐time migration. It inherits the advantages of both ray‐based and wave equation migrations, and produces clear images for complicated structures with fewer artifacts than traditional imaging methods. Plain Language Summary: Seismic ray theory has evolved from classical asymptotic ray theory, through paraxial ray theory and Maslov's method, and then to the Gaussian beam method. Although the computational accuracy of the ray‐based methods for seismic modeling and imaging have been greatly improved, the fundamental high‐frequency approximation still prevents them from accurately describing finite‐frequency wave propagations in complex structures. We introduce the idea of reverse‐time migration into the beam method and develop a two‐way beam wave scheme for seismic modeling and imaging. Local velocities in the vicinity of central rays are first extracted and then the finite‐difference approach is used to solve the wave equation in the ray‐centered coordinate. Accurate wavefield simulation and beam‐to‐beam imaging condition enables us to achieve clear migrated images with fewer artifacts than traditional Gaussian beam migration and reverse‐time migration. Numerical examples for benchmark models and field data demonstrate the feasibility and adaptability of the proposed two‐way beam wave method. Key Points: It is difficult for ray theory to accurately simulate seismic wave phenomena in areas with strong velocity variationsA two‐way beam wave method is proposed to bridge the gap between ray‐based and wave equation approachesA beam wave reverse‐time migration approach is developed to improve the image quality for complicated subsurface environments [ABSTRACT FROM AUTHOR]

The hybridization of abundant transition metals with facile nitrogen‐doped carbons is an effective strategy to fabricate advanced functional materials for targeted applications. Herein, we demonstrate a novel and straightforward synthetic approach of preparing a series of different transition metal‐modified nitrogen‐doped carbons (M/NC, M=Fe, Co, Ni) through the addition of corresponding metal sulfates during the polymerization of aniline, followed by high‐temperature (873–1273 K) pyrolysis treatment. While Fe/NC features predominantly single Fe atoms, nanoparticles of mixed metal oxides and or carbonates are formed on Co/NC and Ni/NC. When employed in the selective oxidation of ethyl benzene by using tert‐butyl hydroperoxide both as the solvent and the oxidant, these materials showed promoted catalytic response with the order of Fe>Co>Ni as compared with the metal‐free analogue. The performance can be further tuned by controlling the pyrolysis temperature, and the best performance can be achieved over Fe/NC‐1273 (0.153 wt.% Fe), affording an unprecedented acetophenone yield of 98 % and excellent cycling performance. [ABSTRACT FROM AUTHOR]

On March 31, 2020, an Mw 6.5 earthquake struck near Stanley, Idaho. More than 35% nondouble‐couple component in long‐period point‐source solutions indicate a more complex source than slip on a planar fault. Using an integrative analysis of seismological and geodetic data, we find that the Stanley earthquake ruptured a pair of opposing‐dip faults offset by a 10‐km‐wide step, including an unmapped northern subfault with predominantly strike‐slip faulting and a southern subfault subparallel to the Sawtooth fault with predominantly normal faulting. This converging fault geometry allowed the rupture to traverse a surficial 10‐km‐wide step, which is greater than the limiting dimension (3–4 km) that commonly ceases earthquake ruptures. This study reveals that a composite rupture process with strike‐slip and normal faulting is typical for earthquakes located near the northern boundary of the Centennial Tectonic Belt (CTB), which is distinct from the predominantly normal faulting in the central CTB. Plain Language Summary: The northwest of Stanley, Idaho, is struck by an Mw6.5 earthquake on March 31, 2020, which is the largest event in Idaho since the 1983 Borah Peak earthquake. This event has several intriguing aspects: (1) the epicenter located by USGS is not on a mapped fault and the source region has little historical seismicity over the past 50 years; (2) it predominantly involves strike‐slip faulting, which is inconsistent with the extensional strain accommodated by the closest Sawtooth fault; (3) long‐period point‐source solutions have more than 35% non‐double‐couple components, indicating a more complex source than slips on a planar fault. Based upon an integrative analysis for both seismological and remote sensing data, we prescribe an opposing‐dip two‐fault model to reconcile all observations. The rupture initiated near the USGS epicenter, and then propagated to the southeast about 20 km along the northerner subfault trajectory. When reaching the northwestern terminus of the Sawtooth fault, the rupture changed its original trajectory and moved southwestward, traversing a 10‐km‐wide step‐over. After passing the mapped Sawtooth fault terminus, it propagated to the southeast about 25 km along the southern subfault, which is subparallel to the Sawtooth fault scarp. Key Points: An integrative analysis is applied for the seismological and geodetic data of the 2020 Stanley, Idaho earthquakeWe found that the Stanley earthquake ruptured a pair of opposing‐dip faults offset by a 10‐km‐wide step that narrows with depthThis study reveals that complicated rupture processes appear to be typical for the earthquakes located near the northern Centennial Tectonic Belt boundary [ABSTRACT FROM AUTHOR]

Several hypotheses have been proposed to explain intriguing circular shear wave splitting patterns in the Pacific Northwest, invoking either 2‐D entrained flows or 3‐D return flows. Here, we present some hitherto unidentified, depth‐dependent anisotropic signatures to reconcile different conceptual models. At depths shallower than 200 km, the fast propagation directions of seismic waves to the west of the Rocky Mountain are aligned sub‐parallel to the subduction direction of the Juan de Fuca and Gorda Plates. This pattern is consistent with previous onshore/offshore shear wave splitting measurements and indicates that 2‐D entrained flows dominate at shallower depths. From 300 to 500 km, two large‐scale return flows are revealed, one circulating around Nevada and Colorado and the other running around the edge of the descending Juan de Fuca slab. These observations suggest the development of toroidal‐mode mantle flows, driven by the fast rollback of the narrow, fragmented Juan de Fuca and Gorda slabs. Key Points: The fast directions are aligned sub‐parallel to the subduction direction of the Juan de Fuca Plates at depths shallower than 200 kmTwo large‐scale return flows are revealed, circulating around the edges of the descending Juan de Fuca and Gorda slabsThe uppermost lower mantle beneath the Cascadian Subduction Zone is dominated by a NE‐SW oriented flow field [ABSTRACT FROM AUTHOR]

To complement velocity distributions, seismic attenuation provides additional important information on fluid properties of hydrocarbon reservoirs in exploration seismology, as well as temperature distributions, partial melting, and water content within the crust and mantle in earthquake seismology. Full waveform inversion (FWI), as one of the state‐of‐the‐art seismic imaging techniques, can produce high‐resolution constraints for subsurface (an)elastic parameters by minimizing the difference between observed and predicted seismograms. Traditional waveform inversion for attenuation is commonly based on the standard‐linear‐solid (SLS) wave equation, in which case the quality factor (Q) has to be converted to stress and strain relaxation times. When using multiple attenuation mechanisms in the SLS method, it is difficult to directly estimate these relaxation time parameters. Based on a time domain complex‐valued viscoacoustic wave equation, we present an FWI framework for simultaneously estimating subsurface P wave velocity and attenuation distributions. Because Q is explicitly incorporated into the viscoacoustic wave equation, we directly derive P wave velocity and Q sensitivity kernels using the adjoint‐state method and simultaneously estimate their subsurface distributions. By analyzing the Gauss‐Newton Hessian, we observe strong interparameter crosstalk, especially the leakage from velocity to Q. We approximate the Hessian inverse using a preconditioned L‐BFGS method in viscoacoustic FWI, which enables us to successfully reduce interparameter crosstalk and produce accurate velocity and attenuation models. Numerical examples demonstrate the feasibility and robustness of the proposed method for simultaneously mapping complex velocity and Q distributions in the subsurface. Key Points: Subsurface velocity and attenuation structures are important for studying hydrocarbon reservoirs, geothermal dynamics, and magma chambersAn inversion scheme is developed for simultaneously mapping P wave velocity and attenuation based on a complex‐valued wave equationAn approximated Gauss‐Newton Hessian is utilized to reduce interparameter crosstalks and produce accurate velocity and attenuation models [ABSTRACT FROM AUTHOR]

Using regional seismic data and a 3‐D crustal velocity model, we develop a novel multiazimuth backprojection approach and apply it to image time‐lapse coseismic ruptures for the 2019 Ridgecrest earthquakes. The time‐integrated images for the Mw6.4 foreshock and Mw7.1 mainshock agree with the fault geometry delineated by the aftershock distributions. Backprojection images at different times illustrate the detailed rupture processes for these two events. For instance, the Mw6.4 foreshock initialized close to the hypocenter, then the rupture propagated along a northwest trending fault with an average velocity of 1.0 km/s, and finally jumped to a southwest trending fault and propagated about 20 km with a velocity about 1.5 km/s. In contrast, the Mw7.1 mainshock initialized near the hypocenter, then propagated to the northwest upon reaching the Coso volcanic field with an average velocity of 1.4 km/s, and later turned to the southeast and propagated along the main fault zone with a complex bilateral process and a velocity about 0.6 km/s. Key Points: We present a novel backprojection approach to image time‐lapse coseismic rupture propagation for the 2019 Ridgecrest earthquake sequenceThe backprojection images agree with the fault geometry determined by the distribution of aftershocksThe time‐lapse images illustrate the detailed rupture processes of the Mw6.4 foreshock and Mw7.1 mainshock [ABSTRACT FROM AUTHOR]

Replacement of noble metal catalysts with low‐cost, non‐noble heterogeneous catalysts is highly desirable. Herein, we prepared a reactive, inexpensive and stable isolated single‐atom Zn/N‐doped porous carbon (ZnNC) catalyst derived from a versatile zeolitic imidazolate framework precursor. The optimized ZnNC‐1000 with Zn‐Nx species possesses high zinc loading (5.2 wt%) and nitrogen content (6.73 wt%), exhibits efficient catalytic performance in the one‐pot N‐formylation of nitroarene to the corresponding formamides by using formic acid as the hydrogen donor and formylation agent. H2‐D2 exchange reaction and HCOOH‐chemisorption experiments demonstrated that atomically dispersed Zn‐Nx species are essential for the activation of hydrogen and HCOOH molecules, which finally contributed to the highest catalytic activity of ZnNC‐1000 for the reductive N‐formylation reaction. [ABSTRACT FROM AUTHOR]

A multifunctional copolymer (PyPPh2-SO3H@porous organic polymers, POPs) was prepared by combining acidic groups and heterogeneous P,N ligands through the copolymerization of vinyl-functionalized 2-pyridyldiphenylphosphine (2-PyPPh2) and p-styrene sulfonic acid under solvothermal conditions. The morphology and chemical structure of the copolymer were evaluated using a series of characterization techniques. Compared with traditional homogeneous Pd(OAc)2/2-PyPPh2/ p-toluenesulfonic acid catalyst, the copolymer supported palladium catalyst (Pd-PyPPh2-SO3H@POPs) exhibited higher activity for alkoxycarbonylation of terminal alkynes under the same conditions. This phenomenon could be attributed to the synergistic effect between the single-site Pd centers, 2-PyPPh2 ligands, and SO3H groups, the outstanding swelling properties as well as the high enrichment of the reactant concentration by the porous catalyst. In addition, the catalyst could be reused at least 4 times without any apparent loss of activity. The excellent catalytic reactivity and good recycling properties make it an attractive catalyst for industrial applications. This work paves the way for advanced multifunctional porous organic polymers as a new type of platform for heterogeneous catalysis in the future. [ABSTRACT FROM AUTHOR]