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.
SummaryExtensional faults in Southern Calabria (Italy) have been widely studied for their capability of generating high magnitude earthquakes (Mw 7-7.2). An example is the historical seismic sequence occurred in 1783, which caused numerous fatalities near the villages located along the longest faults of this region: the Cittanova and the Serre faults. In this work, we estimated the seismic potential of these two faults by a kinematic block modeling approach using GNSS data of both campaign points and permanent stations. Our results indicate that both faults are accommodating the recognized extensional velocity gradient (∼ 1 mm/yr) by long-term slip rates (∼ 2 mm/yr). To estimate the back slip distribution and the interseismic coupling degree of the Cittanova and Serre faults, we discretised these by a triangular dislocation elements (TDEs) mesh. This approach has allowed us to distinguish the fault areas where elastic seismic rupture is more likely to happen from those affected by aseismic creeping behaviour. The obtained results show that the highest values of coupling are located near the shallow portion of the fault planes and near the southern tip of the Cittanova fault. We therefore estimated a set of possible rupture scenarios finding that the Southern Calabria domain is accumulating an interseimic moment rate at most equal to 2.16 ×1016 Nm/yr, the equivalent of an earthquake of Mw 4.86 for each year.
SummaryChemical potentials are defined as the partial derivatives of the Helmholtz energy with respect to moles of chemical components under conditions of zero domain strain and fixed temperature. Under hydrostatic conditions, chemical potentials are dependent only on state properties. Under nonhydrostatic conditions, they also depend on a “chemical expansivity tensor” - a second-order tensor with unit trace that characterises how the elastic network is compressed to accommodate new material within the local domain element. The five degrees of freedom of this tensor generate a class of chemical potentials. An important group within this class are the “uniaxial chemical potentials”, which quantify the Helmholtz energy change when new material is incorporated via compression along a single axis. Chemical and mechanical equilibrium is achieved when all uniaxial chemical potentials remain constant along their respective axes. The derived expressions apply to both crystalline and amorphous materials. Their utility is demonstrated through solutions to classic phase-equilibrium problems.
Pressure on the International Seabed Authority (ISA) to finalize and adopt regulations for deep-sea mining is increasing. While some ISA member states are hoping to see progress soon, a growing number of states are demanding more time to research the environmental impact of mining raw materials on the seabed and to develop an appropriate regulatory framework. What are the legal forms such a delay could take and what would the political consequences be?
Publication date: Available online 26 February 2025
Source: Advances in Space Research
Author(s): Matej Zigo, Jiří Šilha, Katarína Sabolová, Tomáš Hrobár
Publication date: Available online 26 February 2025
Source: Advances in Space Research
Author(s): Bongokuhle S’phesihle Sibiya, John Odindi, Onisimo Mutanga, Moses Azong Cho, Cecilia Masemola
Ventilation is an important process within the global ocean, where waters sink to deeper layers, are transported by deep currents, and eventually get upwelled back to the surface. This process affects the distribution of oxygen and carbon in the global ocean by transporting these elements from the surface to deeper regions of the ocean.
Using a unique field site in the Negev, Ben-Gurion University of the Negev geologists have presented the first-ever time-dependent record of drainage divide migration rates. Prof. Liran Goren, her student Elhanan Harel, and co-authors from the University of Pittsburgh and the Geological Survey of Israel, further demonstrate that episodes of rapid divide migration coincide with past climate changes in the Negev over the last 230,000 years (unrelated to present-day climate change).
Late last year, a massive ocean swell caused by a low pressure system in the North Pacific generated waves up to 20 meters high, and damaged coastlines and property thousands of kilometers from its source.
An international team of scientists has synchronized key climate records from the Atlantic and Pacific Oceans to unravel the sequence of events during the last million years before the extinction of the dinosaurs at the Cretaceous/Paleogene boundary. For the first time, these new high-resolution geochemical records reveal when and how two major eruption phases of gigantic flood basalt volcanism had an impact on climate and biota in the late Maastrichtian era 66 to 67 million years ago.
It is widely believed that Earth's atmosphere has been rich in oxygen for about 2.5 billion years due to a relatively rapid increase in microorganisms capable of performing photosynthesis. Researchers, including those from the University of Tokyo, provide a mechanism to explain precursor oxygenation events, or "whiffs," which may have opened the door for this to occur.
Author(s): Bertrand Martinez, Robert Babjak, and Marija Vranic
Positron creation and acceleration is one of the major challenges for constructing future lepton colliders. On the one hand, conventional technology can provide a solution, but at a prohibitive cost and scale. On the other hand, alternative, reduced-scale ideas for positron beam generation could bri…
[Phys. Rev. E 111, 035203] Published Mon Mar 10, 2025
