Publication date: Available online 27 February 2025
Source: Advances in Space Research
Author(s): He Ren, Haichao Gui, Rui Zhong
Publication date: Available online 27 February 2025
Source: Advances in Space Research
Author(s): Guo Chen, Jun Tao, Na Wei, Qile Zhao
An extraordinary jump in ocean temperatures in 2023 and 2024 was at the extreme end of expectations from global warming and would have been "practically impossible" without climate change, new research said Wednesday.
As climate change continues to drive global sea level rise, many people living in coastal areas are already seeing the effects. Coastal erosion is accelerating and shifting coastlines inland, and storm surges are getting worse. But lurking beneath the surface is another major consequence that is thus far poorly understood: rising groundwater.
Critical minerals such as lithium, cobalt and copper are essential for an energy transition away from fossil fuels—but America's perception of their importance isn't fully understood, which can slow progress.
A recent swarm of small shallow earthquakes in Mexico City in 2019 and 2023 caused surprisingly strong ground shaking, prompting researchers to wonder how shaking from a moderate-sized earthquake might impact buildings across the city.
Princeton University and Xiamen University researchers report that in tropical and subtropical oligotrophic waters, ocean acidification reduces primary production, the process of photosynthesis in phytoplankton, where they take in carbon dioxide (CO2), sunlight, and nutrients to produce organic matter (food and energy).
SummaryIn recent years, Full-Waveform Inversion (FWI) has been extensively used to derive high-resolution subsurface velocity models from seismic data. However, due to the nonlinearity and ill-posed nature of the problem, FWI requires a good starting model to avoid producing non-physical solutions (i.e., being trapped in local minima). Moreover, traditional optimization methods often struggle to effectively quantify the uncertainty associated with the recovered solution, which is critical for decision-making processes. Bayesian inference offers an alternative approach as it directly or indirectly evaluates the posterior probability density function using Bayes’ theorem. For example, Markov Chain Monte Carlo (MCMC) methods generate multiple sample chains to characterize the solution’s uncertainty. Despite their ability to theoretically handle any form of distribution, MCMC methods require many sampling steps; this limits their usage in high-dimensional problems with computationally intensive forward modeling, as is the FWI case. Variational Inference (VI), on the other hand, approximates the posterior distribution in the form of a parametric or non-parametric proposal distribution. Among the various algorithms used in VI, Stein Variational Gradient Descent (SVGD) is characterized for its ability to iteratively refine a set of samples (commonly referred to as particles) to approximate the target distribution through an optimization process. However, mode and variance-collapse issues affect SVGD in high-dimensional inverse problems. In this study, we propose to improve the performance of SVGD within the context of FWI by combining an annealed variant of the SVGD algorithm with a multi-scale strategy, a common practice in deterministic FWI settings. Additionally, we demonstrate that Principal Component Analysis (PCA) can help to evaluate the performance of the optimization process and gain insights into the behavior of the output particles and their overall distribution. Clustering techniques are also employed to provide more rigorous and meaningful statistical analysis of the particles in the presence of multi-modal distributions (as is usually the case in FWI). Numerical tests, performed on a portion of the acoustic Marmousi model using both single and multiple frequency ranges, reveal the benefits of annealed SVGD compared to vanilla SVGD to enhance uncertainty estimation using a limited number of particles and thus address the challenges of dimensionality and computational constraints.
SummaryThe ability to detect low frequency sounds from distant energetic events depends on the temperature and wind structure of the atmosphere. Thus, from time to time surface-based acoustic detectors may not be able to capture sounds arriving from certain directions. However, the temperature minimum at the tropopause may create an acoustic duct called the “AtmoSOFAR” channel that could transmit acoustic waves laterally – but perhaps not to the ground. If true, then elevated sensors such as those borne aloft by balloons would record the signatures even in regions where ground based sensors cannot. This has been difficult to prove because high altitude acoustic sources are rare and balloon deployments are sporadic. This work describes the detection and characterization of powerful acoustic waves generated during the launch and terminal explosion of the SpaceX Starship rocket on 20 April 2023 using a pair of microbarometers on a stratospheric balloon. The signals traveled through the AtmoSOFAR channel, carrying information about the size and nature of their source. This channel also appears to leak some acoustic energy to the ground, in agreement with previous studies. The acoustic yield of the Starship terminal explosion was on the order of 103 tons TNT equivalent, which agrees with the estimated fuel load of the vehicle to about a factor of 2, but is two orders of magnitude larger than optical estimates. These results support an earlier study that claimed lateral transmission of sound from a smaller rocket through the AtmoSOFAR channel. The transmission of source information through the AtmoSOFAR channel motivates its use for monitoring other natural and anthropogenic events using balloon-borne sensors. This may become increasingly important as more and more private and government entities conduct spacecraft launches and reentries. It may also provide a means of monitoring clear air turbulence and other sound-generating atmospheric phenomena at a distance.
SummaryThe Sichuan-Yunnan region is a crucial area for studying the deformation and tectonic evolution of the lithosphere within the Tibetan Plateau. However, a significant controversy exists about the spatial distribution of the low-viscosity zones in its mid-lower crust. Herein, we utilized a combination of topography, geoid height, surface heat flow, and Rayleigh wave phase velocity dispersion curves to ascertain the lithospheric temperature, seismic wave velocity, and density structure in this region. By correlating the inverted velocity and density structures with laboratory measurements of rock velocity and density, we further deduced the lithospheric lithology structure and rheological property of the Sichuan-Yunnan region. Our findings suggest that the lower crust of this region is predominantly composed of felsic granulite. The lower crust of the Qiangtang Block, the Chuan-Xi Block, the Dian-Zhong Block west of the Lvzhijiang fault, and the IndoChina Block exhibit extensive areas with low-viscosity characteristics (<1021 Pa·s). In contrast, the Sichuan Basin, the Eastern Himalayan Syntaxis, and the central region of the Emeishan Igneous Province are characterized by high strength. We argue that the collision between the Indian and Eurasian plates led to the thickening of the Qiangtang Block's crust, producing a large low-viscosity area within the mid-lower crust. The delamination of the IndoChina lithosphere may cause the upwelling of mantle material, thereby weakening the lithosphere of the Dian-Zhong Block west of the Lvzhijiang fault and the IndoChina Block. This study delineates the spatial distribution of low-viscosity zones within the mid-lower crust of the Sichuan-Yunnan region, offering a foundational rheological model that can be instrumental for subsequent seismological and dynamic analyses.
SummaryApplications of spectral induced polarization (SIP) require electrodes that maintain hydrologic contact with surrounding soils to capture small electrical responses, often observed as phase shifts in milliradians. For unsaturated soils, electrodes must overcome the increased electrical contact impedance due to reduced pore fluid. Traditional designs use a ceramic membrane electrode (CME) with a water reservoir and metal conductor, requiring periodic maintenance to retain electrolytic solution. For field applications where maintenance is impractical, alternative designs are needed. This study evaluated a new electrode design (silica flour electrode, SFE) alongside a CME design. SFEs use packed silica flour to store water via capillary forces against a metal conductor. The study examined both designs in three variably saturated soils at soil suctions up to 700 mbar and soil water contents below 1 per cent, with SIP measurements across 0.01 to 10,000 Hz frequencies. SFEs match CMEs at high frequencies and perform better at lower frequencies, without requiring ongoing maintenance, making them ideal for field use. In water-only experiments, CMEs produced errors and high noise below 1.5 Hz, whereas SFEs were more accurate. However, CMEs performed better above 300 Hz. In fine sand, SFEs performed better due to the relatively lower contact impedance as compared to CMEs. Both electrode types performed comparably in silty sand and silt loam soils, although CMEs required ongoing maintenance, suggesting potential for long-term reliability issues.
SummaryThe finite-difference method (FDM), limited by uniform grids, often encounters severe oversampling in high-velocity regions when applied to multi-scale subsurface structures, leading to reduced computational efficiency. A feasible solution to this issue is the use of non-uniform grids. However, previous discontinuous grid approaches required careful consideration of interpolation operations in transition regions, while single-block continuous grids lacked flexibility. This paper proposes a novel approach using multi-block stretched grids with positive and negative singularities to achieve non-uniform grids, the numerical simulation of seismic waves is realized by combining it with the curvilinear grid finite-difference method (CGFDM). Our method facilitates seamless information exchange between coarse and fine grids without additional interpolation or data processing and allows for flexible grid configurations by adjusting singularity pairs.The effectiveness of our approach is verified through comparisons with the generalized reflection/transmission method (GRTM) and the finite-element method (FEM). Numerical experiments demonstrate the method's reliable accuracy and significant reduction in grid points compared to uniform grids. Although the stability of our method has not been rigorously mathematically proven, we demonstrate that the algorithm remains applicable for sufficiently long simulations to address realistic scenarios.
SummaryFor a weakly anisotropic medium, Rayleigh and Love wave phase speeds at angular frequency ω and propagation azimuth ψ are given approximately by V(ω, ψ) = A0 + A2ccos 2ψ + A2ssin 2ψ + A4ccos 4ψ + A4ssin 4ψ. Earlier theories of the propagation of surface waves in anisotropic media based on non-degenerate perturbation theory predict that the dominant components are expected to be 2ψ for Rayleigh waves and 4ψ for Love waves. This paper is motivated by recent observations of the the 2ψ component for Love waves and 4ψ for Rayleigh waves, referred to here as “unexpected anisotropy”. To explain these observations, we present a quasi-degenerate theory of Rayleigh-Love coupling in a weakly anisotropic medium based on Hamilton’s Principle in Cartesian coordinates, benchmarking this theory with numerical results based on SPECFEM3D. We show that unexpected anisotropy is expected to be present when Rayleigh-Love coupling is strong and recent observations of Rayleigh and Love wave 2ψ and 4ψ anisotropy can be fit successfully with physically plausible models of a depth-dependent tilted transversely isotropic (TTI) medium. In addition, when observations of the 2ψ and 4ψ components of Rayleigh and Love anisotropy are used in the inversion, the ellipticity parameter ηX, introduced here, is better constrained, we can constrain the absolute dip direction based on polarization measurements, and we provide evidence that the mantle should be modeled as a tilted orthorhombic medium rather than a TTI medium. Ignoring observations of unexpected anisotropy may bias the estimated seismic model significantly. We also provide information about the polarization of the quasi-Love waves and coupling between fundamental mode Love and overtone Rayleigh waves in both continental and oceanic settings. The theory of SV-SH coupling for horizontally propagating body waves is presented for comparison with the surface wave theory, with emphasis on results for a TTI medium.
An interdisciplinary team affiliated with a host of institutions across China, working with one colleague from Singapore and another from MIT, has found evidence suggesting that if solar panels could be installed on every rooftop in the world, replacing traditional power sources, the result could be a reduction in global surface temperatures by as much as 0.13° C.
A new study has revealed significant changes in the strength and position of the Southern Hemisphere westerly winds over the past 11,000 years.
An influx of salt from both land and sea and a warming world are condemning the world's rivers, streams and estuaries to a "saltier future," according to a new study led by University of Maryland Geology Professor Sujay Kaushal in collaboration with researchers from other institutions.
The Earth is absorbing more sunlight and trapping more heat than it releases into space, causing our planet to warm up at an increasing rate.
A study led by researchers from the Barcelona Institute for Global Health (ISGlobal) has used a novel approach to unravel the influence of the loss of Arctic sea ice on the planet's climate, isolating it from other factors related to climate change.
New research published in the journal Environmental Research Letters reveals that artisan gold mining in the southern Peruvian Amazon has caused more destruction to carbon-rich peatlands in the past two years than in the previous three decades combined, posing a serious threat to the environment and climate.
The mass extinction that ended the Permian geological epoch, 252 million years ago, wiped out most animals living on Earth. Huge volcanoes erupted, releasing 100,000 billion metric tons of carbon dioxide into the atmosphere. This destabilized the climate and the carbon cycle, leading to dramatic global warming, deoxygenated oceans, and mass extinction.
