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Abstract

Trends in the deep-ocean M \(_2\) barotropic tide, deduced from nearly three decades of satellite altimetry and recently presented by Opel et al. (Commun Earth Environ 5:261, https://doi.org/10.1038/s43247-024-01432-5, 2024), are here updated with a slightly longer time series and with a focus on potential systematic errors. Tidal changes are very small, of order 0.2 mm/year or less, with a tendency for decreasing amplitudes, which is evidently a response to the ocean’s increasing stratification and an increasing energy loss to baroclinic motion. A variety of systematic errors in the satellite altimeter system potentially corrupt these small trend estimates. The Dynamic Atmosphere Correction (DAC), derived from an ocean model and used for de-aliasing, introduces a spurious trend (exceeding 0.1 mm/year in places) caused by changes in ECMWF atmospheric tides. Both operational and reanalysis atmospheric tides have spurious trends over the altimeter era. Tidally coherent errors in satellite orbits, including from use of inconsistent tidal geocenter models, are more difficult to bound, although differences between two sets of satellite ephemerides are found to reach 0.1 mm/year for M \(_2\) . Orbit errors are more deleterious for some other constituents, including the annual cycle. Tidal leakage in the “mesoscale correction,” needed here to suppress non-tidal ocean variability, is a known potential problem, and if the leakage changes over time, it impacts ocean-tide trend estimation. Tests show the error is likely small in the open ocean ( \(<0.04\)  mm/year) but large in some marginal seas ( \(>0.2\)  mm/year). Potential contamination from other altimeter corrections (e.g., ionospheric path delay) is likely negligible for M \(_2\) but can be difficult to bound.

SummaryWe conducted comparative measurements of thermal properties of samples from nine cores of the ICDP COSC-1 borehole and four widely used rock references, using a steady-state and a transient divided-bar device, a transient plane source device, a modified Ångström device, as well as two optical thermal conductivity scanners. In addition, a caloric method provided benchmark values for specific heat capacity. A complementary thin-section analysis of the COSC-1 samples allowed us to calculate specific heat capacity according to Kopp’s law and thermal conductivity according to commonly used mixing models. Our results demonstrate agreement between the various test methods within ±10% for about one half of the investigated samples. Furthermore, almost all results for specific heat capacity agree with the predictions of Kopp’s law, though the significance of this correspondence is limited owing to large uncertainties in the experimental and theoretical values. The results for thermal conductivity fall within the most extreme theoretical bounds that account for anisotropy but for an amphibolite. Thermal anisotropy seems to contribute significantly to the deviations between results of the different transient methods that, however, cannot be reconciled by the available theoretical relations for apparent thermal conductivity of transversely isotropic materials. The combination of characteristic investigation volume of the individual methods and sample heterogeneity has to be considered responsible for variability of results, too, an issue whose clarification is calling for dedicated numerical modelling in the future, with the prospect to characterise thermal heterogeneity from observed differences.

SummaryElastodynamic Green’s functions are an essential ingredient in seismology as they form the connection between direct observations of seismic waves and the earthquake source. They are also fundamental to various seismological techniques including physics-based ground motion prediction and kinematic or dynamic source inversions. In regions with established 3D models of the Earth’s elastic structure, such as southern California, 3D Green’s functions can be computed using numerical simulations of seismic wave propagation. However, such simulations are computationally expensive which poses challenges for real-time ground motion prediction and uncertainty quantification in source inversions. In this study, we address these challenges by using a reduced-order model (ROM) approach that enables the rapid evaluation of approximate Green’s functions. The ROM technique developed approximates three-component time-dependent surface velocity wavefields obtained from numerical simulations of seismic wave propagation. We apply our ROM approach to a 50 km × 40 km area in greater Los Angeles accounting for topography, site effects, 3D subsurface velocity structure, and viscoelastic attenuation. The ROM constructed for this region enables rapid computation (≈0.0001 CPU hours) of complete, high-resolution (500 m spacing), 0.5 Hz surface velocity wavefields that are accurate for a shortest wavelength of 1.0 km for a single elementary moment tensor source. Using leave-one-out cross validation, we measure the accuracy of our Green’s functions for the CVM-S velocity model in both the time domain and frequency domain. Averaged across all sources, receivers, and time steps, the error in the rapid seismograms is less than 0.01 cm/s. We demonstrate that the ROM can accurately and rapidly reproduce simulated seismograms for generalized moment tensor sources in our region, as well as kinematic sources by using a finite fault model of the 1987 MW 5.9 Whittier Narrows earthquake as an example. We envision that rapid, accurate Green’s functions from reduced-order modeling for complex 3D seismic wave propagation simulations will be useful for constructing real-time ground motion synthetics and source inversions with high spatial resolution.

SummaryWe aim to improve our comprehension of the seismic process and to identify possible long-term predictability tools of strong earthquakes through the simulation performed by a new-generation simulator code based on a well-elaborated model of the earthquake sources. We applied our previously tested physics-based earthquake simulator to the Nankai megathrust fault system, characterised by a 13 centuries historical record of strong earthquakes. Our results show these significant seismicity patterns characterizing the seismic cycles: the average stress increases almost linearly, while its standard deviation decreases more and more rapidly as the next major earthquake approaches; the co-seismic stress drop and the simultaneous increase of the standard deviation mark the beginning of the new seismic cycle; and the b-value tends to increase some decades before major earthquakes and exhibits correlation with the occurrence rate. Our results encourage further investigations about the application of simulators in support of other methodologies of earthquake forecasting.

SummaryA grain-based stress corrosion model is built from 3DEC-GBM (i.e., a three-dimensional discrete element grain-based model). The model employs the effective stress law and stress corrosion theory to study the time-dependent and time-independent deformation at the mesoscale of the sandstone with varying confining and pore pressures. The simulations adequately explain complex macroscopic time-independent behavior in terms of the mesoscale interaction of grains, and tension cracks were the dominant crack propagation pattern in the simulation for different confining and pore pressures. The traditional creep behavior observed in laboratory brittle creep experiments could also be accurately reproduced by the proposed model. The simulations show that the percentage of tension cracks in rock fractures decreases with increasing confining pressure and pore pressures. Increasing the applied differential stress and reducing the effective pressure can shorten time-to-failure and increase the creep strain rate, respectively. We conclude that the proposed model is an appropriate tool to analyze the deformation behavior of sandstone under coupled hydro-mechanical loading in both the short and long term.

SummaryThis paper introduces a comprehensive framework for modelling both instantaneous and time-dependent elastic softening in anisotropic materials at high pressure and temperature. This framework employs Landau Theory, minimizing the Helmholtz energy by varying isochemical parameters (q) that capture structural changes, atomic ordering, and/or electronic spin states. This allows for internally consistent predictions of volume, unit cell parameters, the elastic tensor, and other thermodynamic properties, while allowing large symmetry-breaking strains. The formulation is validated using the stishovite-to-post-stishovite transition. It is demonstrated that, near this transition, both stishovite and post-stishovite exhibit auxetic behaviour in several directions, with post-stishovite also displaying negative linear compressibility along the long axis of its unit cell (either the a or b axis). The new formulation is implemented in the open-source BurnMan software package.

SummarySeismic and electrical surveys are the most employed geophysical exploration applications for understanding the subsurface earth. Differential effective medium (DEM) models are the models to interpret the seismic and electrical survey data with the greatest success. However, cementation exponent and pore aspect ratio as the indispensable geometric parameters in the electrical and elastic DEM models are independent, making the models not suitable for the joint elastic-electrical modelling, a key requirement for the joint interpretation of seismic and electrical exploration data to better understand the increasingly complex hydrocarbon reservoirs. We show how cementation exponent and pore aspect ratio are correlated in three Berea sandstone samples with changing porosity resulting from varying pore pressure. We find that cementation exponent inverted from the electrical DEM model shows a strong positive linear correlation with pore aspect ratio obtained from the elastic DEM model as an implicit function of porosity induced by increasing pore pressure. We also find that the established linear correlation can enable the DEM models to calculate one physical property (e.g., elastic or electrical) from the geometric parameter describing the other property (e.g., electrical or elastic). The results reveal how the elastic and electrical geometric parameters are linked, and provide a consistent microstructure that enables the existing elastic and electrical DEM models to be suitable for the joint elastic-electrical modelling of rocks undergoing varying pore pressure.

Abstract

Global navigation satellite system (GNSS) Doppler measurements are immune to cycle slips, providing a robust way to detect ionospheric irregularities. This study presents a novel approach to detect equatorial plasma bubble (EPB) using a support vector machine (SVM) algorithm based on the GNSS Doppler measurements. The input of the detector is the Doppler index (DI), which is extracted from the dual-frequency differential Doppler observations. Data from HKWS station located in Hong Kong during 2022 are employed to train the SVM model and validate its performance. The results show the trained SVM model achieves 96.7% validation accuracy of EPB detection. To assess the general capability of the model, EPB events throughout the entire year of 2023 are investigated at both the HKWS station and the HYDE station. The results show the performance of EPB detection by the SVM model using DI is comparable to that of by visually inspecting the total electron content time series based on GNSS carrier-phase measurements. In addition, the characteristics of EPB occurrence are also consistent to previous studies, suggesting the detection results are reliable.

Abstract

Chondritic meteorites (chondrites) contain evidence for the interaction of liquid water with the interiors of small bodies early in Solar System history. Here we review the processes, products and timings of the low-temperature aqueous alteration reactions in CR, CM, CI and ungrouped carbonaceous chondrites, the asteroids Ryugu and Bennu, and hydrated dark clasts in different types of meteorites. We first consider the nature of chondritic lithologies and the insights that they provide into alteration conditions, subdivided by the mineralogy and petrology of hydrated chondrites, the mineralogy of hydrated dark clasts, the effects of alteration on presolar grains, and the evolution of organic matter. We then describe the properties of the aqueous fluids and how they reacted with accreted material as revealed by physicochemical modelling and hydrothermal experiments, the analysis of fluid inclusions in aqueously formed minerals, and isotope tracers. Lastly, we outline the chronology of aqueous alteration reactions as determined using the 53Mn-53Cr and 129I-129Xe systems.

Abstract

It is often accepted that the magnetic field structure of coronal mass ejections (CMEs) is accurately represented by the highly twisted circular cross-section magnetic flux rope model, which is the basis of all most commonly used sketches and representations of CMEs. This paradigm has been developed based on studies in the 1970s and 1980s, and it was the inspiration for a series of fitting models developed in the 1990s and 2000s to provide 3-D visualizations and representations for data obtained by remote sensing and in situ measurements. There has been a wealth of measurements since this paradigm was first developed, in particular numerous multi-point measurements and remote heliospheric observations of CMEs in addition to more physical models and numerical simulations. Taken together, they have demonstrated that such a paradigm, although it provides an explanation for certain CME signatures, is inadequate to represent the complexity of the magnetic field structure in numerous other cases. This manuscript reviews 40 years of continuous observations and ongoing research efforts since the proposal of the highly twisted circular cross-section flux rope model, and presents a more elaborate and realistic representation that better reflects the true complexity of the magnetic ejecta within CMEs.

The vast majority of earthquakes strike inside the Ring of Fire, a string of volcanoes and tectonic activity that wraps around the coastlines of the Pacific Ocean. But when an earthquake hits, the areas that experience the strongest shaking aren't always the places that suffer the greatest damage.

Even though "glacial" is commonly used to describe extremely slow, steady movement, a new study has found that glaciers speed up and slow down on a daily—even hourly—basis in response to changes in air temperature, rainfall and the tides.

An international team of climate scientists has found that dust brought to parts of Europe in 2022 from the Saharan desert was slightly radioactive, but its source was not from French nuclear bomb testing back in the 1960s. In their study, published in the journal Science Advances, the group tested dust samples from multiple sites in Europe.

Early detection of earthquakes could be vastly improved by tapping into the world's internet network with a groundbreaking new algorithm, researchers say.

The deepest regions of Earth's oceans, known as the abyssal and hadal zones, lie at least as far under the water's surface as Mount Rainier's peak rises above the land surface. These great depths of 4,000 or more meters make up one of Earth's least explored frontiers and are home to some of its most extreme environments and habitats.

Analysis of data from NASA radar aboard an airplane shows that the decades-old active landslide area on the Palos Verdes Peninsula has expanded.

A recent study by the Hong Kong University of Science and Technology (HKUST) has revealed a startling public health threat: About 17 million people are at risk of gastrointestinal problems due to excessive sulfate levels in groundwater. This alarming finding emerged from the world's first high-resolution global groundwater sulfate distribution map, launched by the university's School of Engineering.

Earth systems models are an important tool for studying complex processes occurring around the planet, such as those in and between the atmosphere and biosphere, and they help researchers and policymakers better understand phenomena like climate change. Incorporating more data into these simulations can improve modeling accuracy; however, sometimes, this requires the arduous task of gathering millions of data points.

The Greenland Ice Sheet is cracking open more rapidly as it responds to climate change. The warning comes in a new large-scale study of crevasses on the world's second largest body of ice.

Author(s): P. Hadjisolomou, T. M. Jeong, P. Valenta, A. J. Macleod, R. Shaisultanov, C. P. Ridgers, and S. V. Bulanov

The interaction of an ultra-intense laser with matter is an efficient source of high-energy particles, with efforts directed toward narrowing the divergence and simultaneously increasing the brightness. In this paper we report on emission of highly collimated, ultrabright, attosecond γ-photons and g…

[Phys. Rev. E 111, 025201] Published Mon Feb 03, 2025