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.
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.
