Research, published in the journal Scientific Reports, highlights the substantial advantages of using AI models over conventional drought indices in predicting the causes and onslaught of conditions leading to scarcity of rain and water.
Author(s): F. X. Bronold and F. Willert
Employing the invariant embedding principle for the electron backscattering function, we present a scheme for constructing an electron surface scattering kernel to be used in the boundary condition for the electron Boltzmann equation of a plasma facing a semiconducting solid. The scheme takes the so…
[Phys. Rev. E 110, 035207] Published Wed Sep 18, 2024
SummaryThe existence of pores, cracks, and cleavage in rocks results in significant non-linear elastic phenomena. One important non-linear elastic characteristic is the deviation of the stress-strain curve from the linear path predicted by Hooke's law. To provide a more accurate description of the non-linear elastic characteristics of rocks and to characterize the propagation of non-linear elastic waves, we introduce the Preisach-Mayergoyz space model. This model effectively captures the non-linear mesoscopic elasticity of rocks, allowing us to observe the stress-strain and modulus-stress relationships under different stress protocols. Additionally, we analyze the discrete memory characteristics of rocks subjected to cyclic loading. Based on the Preisach-Mayergoyz space model, we develop a new non-linear elastic constitutive relationship in the form of an exponential function. The new constitutive relationship is validated through copropagating acousto-elastic testing, and the experimental result is highly consistent with the data predicted by the theoretical non-linear elastic constitutive relationship. By combining the new non-linear elastic constitutive relationship with the strain-displacement formula and the differential equation of motion, we derive the non-linear elastic wave equation. We numerically solve the non-linear elastic wave equation with the finite difference method and observe two important deformations during the propagation of non-linear elastic waves: amplitude attenuation and dispersion. We also observe wavefront discontinuities and uneven energy distribution in the 2-D wavefield snapshot, which are different from those of linear elastic waves. We qualitatively explain these special manifestations of non-linear elastic wave propagation.
SummaryNumerical simulations of seismic wave propagation in heterogeneous 3D media are central to investigating subsurface structures and understanding earthquake processes, yet are computationally expensive for large problems. This is particularly problematic for full waveform inversion, which typically involves numerous runs of the forward process. In machine learning there has been considerable recent work in the area of operator learning, with a new class of models called neural operators allowing for data-driven solutions to partial differential equations. Recent works in seismology have shown that when neural operators are adequately trained, they can significantly shorten the compute time for wave propagation. However, the memory required for the 3D time domain equations may be prohibitive. In this study, we show that these limitations can be overcome by solving the wave equations in the frequency domain, also known as the Helmholtz equations, since the solutions for a set of frequencies can be determined in parallel. The 3D Helmholtz neural operator is 40 times more memory-efficient than an equivalent time-domain version. We employ a Helmholtz neural operator for 2D and 3D elastic wave modeling, achieving two orders of magnitude acceleration compared to a baseline spectral element method. The neural operator accurately generalizes to variable velocity structures and can be evaluated on denser input meshes than used in the training simulations. We also show that when solving for wavefields strictly on the surface, the accuracy can be significantly improved via a graph neural operator layer. In leveraging automatic differentiation, the proposed method can serve as an alternative to the adjoint-state approach for 3D full-waveform inversion, reducing the computation time by a factor of 350.
SummarySignificant compositional differences may exist in the lithospheric mantle and above the core-mantle boundary (CMB) relative to the ambient mantle. The intrinsic density differences may affect the development of thermal boundary layer (TBL) instabilities associated with lithospheric delamination and formation of thermochemical plumes. In this study, we explored the instability of two-layer thermochemical fluid using two different techniques: marginal stability analysis with a propagator-matrix method and finite element modeling. We investigated both the instabilities in lithospheric mantle (i.e., lithospheric instability) and the mantle above the CMB (i.e., plume-forming instability) using a background temperature Tbg(z) with the TBL. For lithospheric instability, we found that two-layer fluid with free-slip boundary conditions mainly undergoes the same three different convective modes (i.e., two oscillatory convection modes and one layered convection regime) as that with no-slip boundary condition reported in Jaupart et al., (2007). However, with free-slip boundary conditions, the transitions between these convection modes occur at larger values of buoyancy number B. Free-slip boundary conditions lead to smaller critical Rayleigh number Rac, but larger convective wavelength and oscillation frequency ωc, compared with those with no-slip boundary conditions. Our numerical modeling results demonstrate that Rac and ωc predicted from the classical marginal stability analyses using Tbg(z) with TBL temperature may have significant errors when the oscillatory period is comparable with or larger than the timescale of lithospheric thermal diffusion that causes Tbg(z) to vary with time significantly. In this case, using a more gently sloped background temperature profile ignoring the TBL temperature, the stability analysis predicts more accurate stability conditions, thus presenting an effective remedy to the stability analysis. For plume-forming instability, because of the reduced viscosity in the hot and compositionally dense bottom layer, the transition to the layered convection occurs at significantly smaller B values, and in the oscillatory convection regime, Rac is larger but ωc is smaller, compared with those for lithospheric instability. Finally, our study provides a successful benchmark of numerical models of thermochemical convection by comparing Rac and ωc from numerical models with those from the marginal stability analysis.
Nature Geoscience, Published online: 18 September 2024; doi:10.1038/s41561-024-01540-z
China’s second phase of clean air actions proved less effective than the first, highlighting the need to adapt and update policies to enable continued progress, according to an assessment combining chemical transport modelling and emission inventories.
As urban centers in mountainous regions grow, more people are driven to build on steeper slopes prone to slow-moving landslides, a new study finds. Slow-moving landslides are frequently excluded from estimates of landslide risk, but they could threaten hundreds of thousands of people globally, the researchers conclude.
Abstract
Employing high precise positioning ability, the global navigation satellite systems (GNSS) could accurately capture subtle deformations in bridges, supplying critical data for structural health monitoring. However, GNSS antennas placed on bridges often encounter multipath interference generated by bridge deck and water surface reflections, compromising the quality of observation data and positioning accuracy. Through the analysis of GNSS data collected from an operational bridge and an oceanic construction platform, we discovered a strong correlation between pseudorange multipath and carrier multipath components. Subsequently, through a series of steps including phase adjustment, decorrelation, and resolution, we successfully mitigated the multipath within residuals, and then reconstructed the corrected residuals into displacements; in addition, the method does not require advance deployment of GNSS equipment to collect calibration information. In terms of positioning results, the proposed method improves the accuracy by 27.1–32.1% in the WLMS (Weighted Least-Mean-Square) resolution and by18.8–32.9% in KF (Kalman Filter) resolution, effectively weakening the multipath interference in carrier phase observations and significantly improving positioning accuracy.
Nature Geoscience, Published online: 17 September 2024; doi:10.1038/s41561-024-01542-x
Enhancing nitrogen use efficiency can effectively reduce soil nitrogen losses from fertilizer use in the production of maize and wheat, according to a global analysis of field measurement data on crop-specific soil nitrogen losses.
SummaryIn the Northern Andes, partitioning of oblique subduction of the Nazca plate beneath the South American continent induces a northeastward motion of the North Andean Sliver. The strain resulting from this motion is absorbed by crustal faults, which have produced magnitude 7 + earthquakes historically in the Andean Cordillera of Ecuador and southern Colombia. In order to quantify the strain in that area, we derive a high-resolution surface velocity map using InSAR time-series processing. We analyzed 6 to 8 years of Sentinel-1 data and combined different satellite line-of-sight directions to produce a reliable velocity map in the East direction. We use interpolated GNSS data to express the velocity map with respect to Stable South America and remove the long-wavelength pattern due to the post-seismic deformation following the 2016 Mw 7.8 Pedernales earthquake. The InSAR velocity map finds high E-W shortening strain rates along N-S trending structures within the Western Cordillera and the Interandean valley, with little deformation taking place east of them. This result strengthens the previous proposition of a ∼350 km long Quito-Latacunga tectonic block, forming a restraining bend in the overall right-lateral strike-slip fault system accommodating the northeastward escape motion of the North Andean Sliver. However, the high spatial resolution provided by InSAR indicates that previously proposed boundaries for this block need to be revised. In particular, InSAR results highlight high strain rate (>300 nstrain/yr) along undescribed active structures, south and west of the proposed limits for the Quito-Latacunga block, respectively in Peltetec and Ibarra regions. Interestingly, the two areas with the largest strain rates spatially correlate with the proposed areas of large historical earthquakes. Modeling of the InSAR and GNSS velocities in these areas suggests shallow coupling and high slip rates on structures which, previously, were not identified as active. We also demonstrate a slow-down of the shallow aseismic slip on the Quito fault after the Pedernales earthquake, suggesting that stress changes following large megathrust events might trigger transient slip behaviors on crustal faults. The high-resolution strain map provided by this work provides a new basis for future tectonic models in the Ecuadorian and southern Colombian Andes, and will contribute to the seismic hazard assessment in this highly populated area of the Andes.
SummaryThe grid search method is a common approach to estimate the three spatial coordinates of event hypocenters. However, locating events in large search spaces with small grid spacings is computationally prohibitive. This study accelerates the grid searches over large search spaces using a quadratic interpolation technique. We start with the coarse-grid-estimated location, where we have the minimum value of the difference in the traveltimes between S- and P-waves summed over all receivers. Then, we select the neighbouring grid points and build a 3D quadratic function. The unknown coefficients of the 3D quadratic function are computed by solving a system of linear equations. After that, we interpolate the location by solving partial derivatives of the quadratic function. The quadratic interpolation technique performs well on both synthetic and real microseismic data examples, typically leading to similar event locations as those obtained using 10 times smaller grid spacings in all three directions, at a minor additional computational expense, and without the need to generate traveltimes at new spatial positions.
Abstract
Here we review the origin, evolution, and compositional properties of Saturn’s ring moons. This class of eleven small satellites includes objects orbiting near the outer edge of the main rings (Pan, Daphnis, Atlas, Prometheus, Pandora, Janus, Epimetheus) and “ring-embedded” moons (Aegeon, Methone, Anthe, Pallene) orbiting inward of Enceladus and associated with either diffuse or partial rings. We discuss current formation scenarios, according to which ring moons could originate either in the main rings from accretion onto original seeds denser than the ring material, or outside the A ring from spontaneous accretion of ring particles, and then evolve outwards due to gravitational torque from the rings. Remote sensing observations of the ring moons from the Cassini mission are analyzed in the broader context of Saturn’s icy moons and main rings observations. Spectroscopic data support a compositional paradigm similar to the main rings, dominated by water ice, and smaller amounts of two separate contaminants, in the form of a UV absorber and a spectrally neutral darkening material. Global radial trends in the spectral properties of the ring moons suggest that the surface composition is significantly affected by a complex interplay of exogenous processes, among which the contamination from nearby A ring particles, meteoritic bombardment, charged particle flux, and E ring particle accumulation, depending on the corresponding magnitude at the ring moon orbital distance and exposure time. These processes modify the original composition inherited by the rings and, coupled with the fact that the surface composition is likely representative only of the ring moon outer layers, make it difficult to trace back the present composition to a given ring moon formation scenario.
New research led by the University of Pittsburgh shows that state and federal appropriations allowing Pennsylvania to treat abandoned mine drainage works to both successfully and cost effectively clean up the acidic water—particularly to the benefit of affected vulnerable communities. But their research also shows that current appropriations to the state are insufficient for long-term treatment of all mine drainage while also needing to address other abandoned mine hazards such as sinkholes.
Like many natural phenomena, precipitation can be both a blessing and a scourge to human life. On the one hand, it supplies our rivers and fields with water; on the other hand, it can cause floods, landslides, and other natural disasters. Either way, understanding and predicting the different types of precipitation is essential.
A study published in the journal Earthquake Research Advances sheds light on the relationship between the 2024 magnitude 7.6 Noto Hanto earthquake and a sizable earthquake swarm that began beneath Japan's Noto Peninsula in November 2020.
The Southern Annular Mode (SAM), with an iconic dipolar zonal wind pattern centered around the axis of the storm track, is the most dominant mode of variability orchestrating the weather and wind from the subtropics to the poles. Its origin, maintenance and feedback have been one of the central themes of atmospheric dynamics. But what role the clouds play in the life cycle of the annular mode remains largely unknown until now, while the wind pattern associated with SAM has long been observed to organize the distribution of cloud in the storm track.
Around 252 million years ago, the world suddenly heated up. Over a geologically brief period of tens of thousands of years, 90% of species were wiped out. Even insects, which are rarely touched by such events, suffered catastrophic losses. The Permian-Triassic mass extinction, as it's known, was the greatest of the "big five" mass extinctions in Earth's history.
Publication date: Available online 12 September 2024
Source: Advances in Space Research
Author(s): Simon Wing, Georgios Balasis
Publication date: Available online 12 September 2024
Source: Advances in Space Research
Author(s): Luis Sánchez, Massimiliano Vasile, Silvia Sanvido, Klaus Merz, Christophe Taillan
Publication date: Available online 12 September 2024
Source: Advances in Space Research
Author(s): Chunhua Jiang, Lehui Wei, Tatsuhiro Yokoyama, Rong Tian, Tongxin Liu, Guobin Yang
