Publication date: 1 February 2025
Source: Advances in Space Research, Volume 75, Issue 3
Author(s): Masahiro Fujita, Hajime Yano, Yuichi Tsuda
SummaryThe causes of intraplate volcanoes in northeastern (NE) China and, in particular, how asthenospheric upwelling interacts with the lithosphere remain poorly constrained. In this study, we use teleseismic data to measure the phase and group velocities of Rayleigh and Love waves, and invert for the shear wave velocity and radial anisotropy within the crust and uppermost mantle. Our results show that there are significant low-velocity anomalies and negative radial anisotropy to the northeast of Changbaishan, suggesting an asthenospheric melt reservoir. This is underlain by mantle upwelling, with regional lithospheric structure focusing melt beneath the volcano. In addition, our results show a high-velocity body in the mantle beneath the southwestern Songliao Basin. This exhibits negative radial anisotropy at its margins, suggesting vertical flow. We suggest that lithospheric delamination here may drive intraplate volcanism beneath the Great Xing'an range.
SummaryLong-period underside SS wave reflections have been widely used to furnish global constraints on the presence and depth of mantle discontinuities and to document evidence for their origins, e.g., mineral phase-transformations in the transition zone, compositional changes in the mid-mantle, and dehydration-induced melting above and below the transition zone. For higher-resolution imaging, it is necessary to separate the signature of the source wavelet (SS arrival) from that of the distortion caused by the mantle reflectivity (SS precursors). Classical solutions to the general deconvolution problem include frequency-domain or time-domain deconvolution. However, these algorithms do not easily generalize when (1) the reflectivity series is of a much shorter period compared to the source wavelet, (2) the bounce point sampling is sparse, or (3) the source wavelet is noisy or hard to estimate. To address these problems, we propose a new technique called SHARP-SS: Sparse High-Resolution Algorithm for Reflection Profiling with SS waves. SHARP-SS is a Bayesian deconvolution algorithm that makes minimal a-priori assumptions on the noise model, source signature, and reflectivity structure. We test SHARP-SS using real data examples beneath the NoMelt Pacific Ocean region. We recover a low-velocity discontinuity at a depth of ∼69 ± 4 km which marks the base of the oceanic lithosphere, consistent with previous work derived from surface waves, body wave conversions, and ScS reverberations. We anticipate high-resolution fine mantle stratification imaging using SHARP-SS at locations where seismic stations are sparsely distributed.
A new study introduces the Community Land Active Passive Microwave Radiative Transfer Modeling platform (CLAP)—a unified multi-frequency microwave scattering and emission model designed to revolutionize land surface monitoring. This cutting-edge platform combines active and passive microwave signals to offer potentially accurate simulations of soil moisture and vegetation conditions.
In the delicate balancing act between human development and protecting the fragile natural world, sand is weighing down the scales on the human side.
The impending loss of the Amazon rainforest due to deforestation has concerned scientists, activists, and citizens all over the globe. Natural habitats sustaining the region's incomparable biodiversity and important carbon stores are at stake, with far-reaching implications for the global climate.
A new USC study reveals a dramatic surge in building collapses in the ancient Egyptian port city of Alexandria, directly linked to rising sea levels and seawater intrusion.
A study published in Geophysical Research Letters has challenged the conventional understanding of the relationship between global warming and ocean evaporation. A research team from the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences discovered a phenomenon that, despite rising sea surface temperatures, global ocean evaporation has decreased over the past decade.
Author(s): B. Arnold, J. Daligault, D. Saumon, Antoine Bédard, and S. X. Hu
Nucleation in the supercooled Yukawa system is relevant for addressing current challenges in understanding a range of crystallizing systems including white dwarf (WD) stars. We use both brute force and seeded molecular dynamics simulations to study homogeneous nucleation of crystals from supercooled…
[Phys. Rev. E 111, 025206] Published Fri Feb 21, 2025
Author(s): C. Ruyer, P. Loiseau, D. Turnbull, and V. Tikhonchuk
The modeling of a spatially incoherent laser beam remains a central problem of the parametric instabilities in the context of inertial confinement fusion. This paper gives a simplified and comprehensive overview of the recent analytical developments regarding the modeling of these laser beams and a …
[Phys. Rev. E 111, 025207] Published Fri Feb 21, 2025
A new study led by the University of Cambridge has revealed that as our springs and summers get hotter and drier, the UK wildfire season is being stretched and intensified. More fires, taking hold over more months of the year, are causing more carbon to be released into the atmosphere as carbon dioxide.
The Mw 7.5 Noto Peninsula earthquake, which occurred on January 1, 2024, was considerably hazardous to the peninsula and surrounding regions owing to a strong motion, large-scale crustal deformation, and subse...
SummaryReflection imaging at volcanoes presents significant challenges due to the highly heterogeneous subsurface, which generates complex wavefields characterized by substantial wave scattering. These scattered waves obscure coherent energy, such as reflections from geological structures in the subsurface. In this study, we develop processing strategies to address the limitations of high-frequency (5-20 Hz) passive reflection imaging at Krafla, a volcanic caldera in NE Iceland. Krafla is among the few locations worldwide where magma has been encountered at 2.1 km depth when drilling the IDDP1 borehole. We analyze over 300 local microearthquakes and industrial noise recorded during five weeks in the summer of 2022. We show that wavefields lack coherency even between stations spaced at 30-meter intervals due to the dominance of site effects beneath the stations. However, data coherency improves in the common-station domain, where different earthquakes recorded by a fixed station are analyzed, thereby stabilizing the site effect. Spectral analyses in this domain reveal that site effects are partly due to resonances at the stations, likely caused by lava flows and cavities in the heterogeneous near-surface. By constructing a resonance removal filter, we successfully deconvolve resonance effects from the data, revealing previously masked coherent energy. We further reduce site effects by applying linear stacking of clustered earthquake traces and non-linear amplitude weighting. Our approach significantly enhances coherency between stations and enables the identification of reflections in microearthquakes likely originating from the known magma-rock interface beneath the IDDP1 borehole.
SummaryIn seismology, wavefield injection refers to the propagation of seismic waves generated by remote sources into local domains bounded by enclosed surfaces. The simulations of wavefield injection, primarily focused on the interaction between incoming seismic waves and local structures, are key to earthquake hazard modeling and full-waveform seismic tomography using tele-seismic waves. In this paper, we show that simulating wavefield injection is equivalent to solving the wave equation subject to interface discontinuity conditions. To provide a general framework to study wavefield injection, we formally define the interface discontinuity problem, and discuss its representation theorem and uniqueness. We also develop an efficient interface-discontinuity-based numerical algorithm to solve the wavefield injection problem through implementations of spectral-element methods, and show with numerical examples that wavefield injection can be accurately simulated at different scales with this algorithm. Under this framework, we draw connections with previously proposed wavefield injection algorithms/hybrid methods, and clarify several theoretical questions on wavefield injection from previous research. We demonstrate the efficiency and accuracy of our approach through wavefield injection examples at local and continental scales. Furthermore, we illustrate the applicability of the interface discontinuity approach to performing kinematic fault simulations through an numerical example.
SummaryThe time-varying geomagnetic field is a superposition of contributions from multiple internal and external current systems. A major source of geomagnetic variations at periods less than a few years are current systems external to the solid Earth, namely the ionospheric and magnetospheric currents, as well as associated induced currents. The separation of these three sources is mathematically underdetermined using either ground or satellite measurements alone, but becomes tractable when the two datasets are combined. Based on this concept, we developed a new geomagnetic field modelling approach that allows us to simultaneously characterise the mid-latitude ionospheric, magnetospheric and the internal induced magnetic fields using ground and satellite observations for all local times and magnetic conditions, and without prescribing any harmonic behaviour on these current systems in time, as is typical in other models. By applying this new method to a 10-year dataset of ground observatory and multi-satellite measurements from 2014 to 2023, we obtained the time series of the spherical harmonic coefficients of the ionospheric, magnetospheric and induced fields. These new time series allow the study of complex non-periodic dynamics of the external magnetic fields during global geomagnetic storms, as well as periodicities in the magnetospheric coefficients linked to solar activities and periodic ionospheric magnetic fields linked to lunar daily variations, contributing to a more complete picture of the dynamics of the external currents and magnetosphere-ionosphere interactions, and facilitating more accurate space weather nowcast and forecast. Finally, the new approach allows for a better characterisation of internal induced field sources, leading to higher quality electromagnetic transfer functions.
SummaryThis paper examines the linear stability of sliding on faults embedded in a 2D elastic medium that obey rate and state friction and have a finite length and/or are near a traction-free surface. Results are obtained using a numerical technique that allows for analysis of systems with geometrical complexity and heterogeneous material properties; however only systems with homogeneous frictional and material properties are examined. Some analytical results are also obtained for the special case of a fault that is parallel to a traction-free surface. For velocity-weakening faults with finite length, there is a critical fault length L* for unstable sliding that is analogous to the critical wavelength h* that is usually derived from infinite fault systems. Faults longer than L* are linearly unstable to perturbations of any length. On vertical strike-slip faults or faults in a full-space L* ≈ h*/e, where e is Euler’s number. For dip-slip faults near a traction-free surface L* ≤ h*/e and is a function of dip angle β, burial depth d of the fault’s up-dip edge, and friction coefficient. In particular, L* is at least an order of magnitude smaller than h* on shallowly dipping (β < 10○) faults that intersect the traction-free surface. Additionally, L* ≈ h*/e on dip-slip faults with burial depths d ≥ h*. For sliding systems that can be treated as a thin layer, such as landslides, glaciers, or ice streams, L* = h*/2. Finally, conditions are established for unstable sliding on infinitely-long, velocity-strengthening faults that are parallel to a traction-free surface.
Nature Geoscience, Published online: 21 February 2025; doi:10.1038/s41561-025-01653-z
Quartz-rich clasts in Martian meteorite NWA 7533 indicate the presence of granitic rocks on early Mars that formed via hydrothermal activity and impact melting, according to petrologic and in situ geochemical analyses.
As part of a multi-pronged approach toward curbing the effects of greenhouse gas emissions, scientists seek to better understand the impact of rising carbon dioxide (CO2) levels on terrestrial ecosystems, particularly tropical forests. To that end, climate scientist César Terrer, the Class of 1958 Career Development Assistant Professor of Civil and Environmental Engineering (CEE) at MIT, and colleague Josh Fisher of Chapman University are bringing their scientific minds to bear on a unique setting—an active volcano in Costa Rica—as a way to study carbon dioxide emissions and their influence.
Publication date: 15 March 2025
Source: Earth and Planetary Science Letters, Volume 654
Author(s):
Publication date: 15 March 2025
Source: Earth and Planetary Science Letters, Volume 654
Author(s): Leslie Insixiengmay, Lars Stixrude
