Author(s): Xiongdong Yu, Zhigang Yuan, Dedong Wang, Oliver Allanson, and Samuel Hunter
The dynamics of electrons in space plasmas, such as the earth’s radiation belts, are affected by the presence of wave turbulence, even when a resonance condition is not satisfied. The authors propose an expression to describe this resonance broadening effect, and find that it compares well with test particle simulation results. The study is applied to whistler-mode chorus waves in the radiation belt’s electrons, but can be easily extended to a wide range of systems.
#AdvancingField #TechnicalAdvancement
[Phys. Rev. E 111, L033201] Published Tue Mar 18, 2025
The natural process of locking away carbon dioxide (CO2) appears to be in decline—and climate change will accelerate as a result, a University of Strathclyde study warns.
Over the last 40 years, the majority of the world's lakes have changed color, according to a new study. The research team analyzed 32 million satellite observations from over 67,000 lakes. Major changes in the lake ecosystems are thought to be the cause.
Between 15,000 and 8,000 years ago, the Earth experienced significant climatic changes, including the rapid retreat of ice sheets and rising sea levels, during the Glacial–Holocene transition. This period featured abrupt climatic events such as the Bølling–Allerød warm period and the Younger Dryas (YD) cold reversal, highlighting shifts from glacial to interglacial conditions.
Author(s): Thomas Chuna and Michael S. Murillo
A considerable number of semiempirical and first-principles models have been created to describe the dynamic response of a collisionally damped charged-particle system. However, known challenges persist for established dynamic structure factors (DSFs), dielectric functions, and conductivities. For i…
[Phys. Rev. E 111, 035206] Published Mon Mar 17, 2025
Could lumpy metallic rocks in the deepest, darkest reaches of the ocean be making oxygen in the absence of sunlight?
SummaryHigh-resolution seismic tomographic images of active fault zones are essential for linking physical processes and observations during large ruptures. The 1999 Izmit and Düzce earthquakes offer a valuable opportunity to study local fault geology, fault structure, and rupture characteristics. By analyzing seismic data from the aftershocks of these earthquakes and long-term seismic observations in the region, I computed P-wave velocity variations along ∼160 km long ruptured segments of the NAF at km-scale resolution.The large velocity perturbations (±10 per cent) at depths of less than 5 km are associated with known geological structures alongside the fault zone. Lower velocities are observed in the Çınarcık, Izmit, Adapazarı, and Düzce basins, while higher velocities are associated with the metamorphic and ultramafic rocks of the Armutlu-Almacık zone.A sharp velocity contrast (±10 per cent) is observed along the 1999 Izmit rupture zone at depths of less than 5 km, but this contrast diminishes at greater depths. The Izmit rupture zone does not hold a large-scale bi-material interface but instead exhibits heterogeneties on shorter length scales. The low-velocity fault zones, ∼3 km thick, detected only in a limited section of the rupture zone.The Almacık block, with its high-velocity core (6.0–6.6 km/s) extending to a depth of about 13 km, plays a crucial role in shaping the multiple branches of the NAF and in the partitioning of strain. The rupture arrests of both 1999 Izmit and Düzce earthquakes occurred in the transition of Düzce and Karadere faults, where a transtensional structure develops at depth of 8-12 km within the zone along the northern boundary of the Almacık block.There appears to be a link between the coseismic slip during the Izmit earthquake and P-wave velocity gradient along the fault zone. Nonetheless, this apparent correlation requires further evaluation through dynamic rupture simulations.
SummaryA problem of growing importance in earthquake forecasting is how to compare probabilistic forecasting models with deterministic physical simulations and extract physical insights from their differences. Here we compare the time-independent Uniform California Earthquake Rupture Forecast Version 3 with a long earthquake catalog simulated by the multi-cycle Rate-State Quake Simulator (RSQSim). Shaw et al. (2018) generated a million-year rupture catalog for California from RSQSim simulations based on UCERF3 fault geometries and slip rates and found that the shaking hazard from the synthetic catalog was in good agreement with the UCERF3 hazard maps. We take this model-to-model comparison to the more granular level of individual faults and ruptures. We map RSQSim ruptures from the Shaw18 catalog onto equivalent UCERF3 ruptures by maximizing the mapping efficiency and ensuring that every RSQSim realizations is associated with a unique UCERF3 rupture. The full UCERF3 logic tree is used to approximate the prior distributions of individual rupture rates and fault subsection participation rates as independent gamma distributions. We formally test the ontological null hypothesis (ONH) that the empirical RSQSim rupture counts are statistically consistent with the UCERF3 rate distributions, given the sampling uncertainty of the RSQSim catalog and the epistemic uncertainty of the UCERF3 model. Testing individual rupture rates provides little evidence either for or against the ONH, owing to the predominance of large ruptures with low recurrence rates. However, at the subsection level, the statistically significant discrepancies are much more common than expected under the ONH. We obtain a 25% failure rate at the 5% significance level and a 15% failure rate at 1% level. The false discovery rates estimated by q-value calculations are low, so we can be confident that the same subsections would likely fail if tested against an independent million-year catalog generated by the same RSQSim model. Bayesian recalibration of the UCERF3 priors using the empirical RSQSim rates yields Gamma posterior distributions that can be derived analytically. The results of testing and recalibration, taken together, quantify how well RSQSim rupture rates agree with, and differ from, the UCERF3 forecast rates. We find that some of the discrepancies can be attributed to the differences in slip rates that drive the models, whereas others are governed by the RSQSim fault dynamics absent from UCERF3.
SummaryConstraining the knowledge of deep aquifer structure in the Angad Basin (Northeastern Morocco) remains one of the major challenges for successful borehole drilling projects. This study demonstrates how integrating gravity and electrical data can enhance subsurface geological imaging and provide valuable insights into geological structures relevant to groundwater exploration. Various gravity enhancement techniques, including vertical gradient, horizontal gradient, upward continuation, logistic filter, tilt angle, and Euler Deconvolution, have been applied to gravity data in the Angad Basin to identify gravity anomalies and tectonic discontinuities. The resulting gravity maps reveal two elongated depressions trending in the NE-SW direction: the Beni Drar depression in the north and the Oujda depression in the south. Both depressions are delineated by strong gravity gradients, indicating the presence of faults. Multiscale analysis of gravity lineaments highlighted sharper features and identified two principal orientations: N070°–085° and N040°–050°, with the latter being more predominant. Faults striking in the N120°–140° are less prominent. These fault systems play a crucial role in dividing the bedrock into distinct horst and graben structures, aligning with the regional tectonic phases observed in northeastern Morocco. The faults are generally sub-vertical, with estimated depth values ranging from 1 000 to 2 680 meters for 42 per cent of the lineaments. Additionally, the reinterpretation of Vertical Electrical Soundings (VES) using 2D inversion methodology provides insight into subsurface resistivity variations. The 2D resistivity sections generated from this process illustrate vertical and lateral variations in electrical resistivity over distances of up to 30 km and depths of up to 2 km, revealing the geological layers that form the aquifer. These resistivity sections confirm the presence of multiple faults that significantly influence the structural configuration of the study area, validating the geometry of the two depressions previously identified through gravity data. The 2D gravity modeling further corroborates and reinforces the findings from the resistivity section inversion, demonstrating that the shape of the residual gravity anomaly curve closely aligns with the morphology of the Jurassic roof structure. The results of this study highlight the complementarity and effectiveness of these two geophysical methods in advancing our understanding of the deep geological structure of the Angad Basin, particularly within the Jurassic limestone, which serves as the region's primary deep aquifer. These findings provide valuable insights for future hydrogeological research in the area.
SummaryUnderstanding the Earth's magnetic field through regional records of secular variation is essential for deciphering its short-term behaviour. This study presents an archaeomagnetic and rock-magnetic investigation of archaeological artefacts from Vadnagar, Gujarat, and introduces India's first continuous palaeosecular variation (PSV) curve for the last four millennia. Detailed rock magnetic analyses were applied to investigate the suitability of the artefacts for intensity measurements. The geomagnetic field intensity was calculated using the Thellier-Thellier method modified by Coe, with cooling rate and anisotropy of the thermoremanent magnetization (ATRM) corrections. A total of 80 independent fragments were analyzed, from which 66 gave positive responses, resulting in a success rate of 83 per cent after the application of corrections and quality selection criteria. Seven new archaeointensities were calculated, with values ranging from 33.58 ± 2.0 to 43.37 ± 1.9 µT. The new intensities were integrated with previously published data in order to construct India's first PSV curve from 2250 BCE to 2000 CE at the geographical Centre of India (20.5937° N, 78.9629° E) using two different modelling approaches. The first approach employs a bootstrap algorithm, yielding relatively smooth intensity variations, while the second utilizes a transdimensional Bayesian framework, producing sharper variations with occasionally greater amplitudes. The PSV curve developed using the bootstrap algorithm was compared with global models, showing precise temporal alignment only from 400 BCE to 200 CE. This indicates the necessity of new reliable archaeointensity data from dated artefacts in order to acquire a rigorous explanation of geomagnetic field intensity change during the past and gain a deeper understanding of local geomagnetic field variations in India.
SummaryIn this study, we illustrate the application of a 3D reflection oriented workflow for full waveform inversion (FWI) to the offset data from the Sleipner field. The data set is having maximum offset of less than 2000 m, and has been pre-processed with a low-cut filter below 6 Hz, imposing strong challenges for the FWI application. To tackle these challenges, a reflection oriented full waveform inversion is applied to the data set, which utilize joint full waveform inversion (JFWI) to constrain the low wavenumber updates at the deepest part of the reconstructed model. It consists of two steps, an impedance model building serving as a prior reflector information followed by a velocity model building. In this case, JFWI workflow is taking advantage of the pseudo-time formulation to honor the zero offset travel time, fast and robust asymptotic preconditioner for impedance model building, and graph space optimal transport misfit function to mitigate cycle skipping. To show the effects of limited offset, conventional FWI is performed. In this case, it is clear that the meaningful updates coming from the diving waves are restricted to the shallow part no deeper than 500 m of depth, while no meaningful perturbation are observed beyond the diving waves penetration. Taking advantage of the meaningful shallow updates, diving wave only inversion is performed prior to the impedance model building, and then followed by the JFWI workflow. The results of the field data application show that JFWI is able to produces meaningful velocity updates both in shallow part and the deeper part. The result is supported by satisfactory fit of the calculated data based on the JFWI model compared to the observed data. In addition, the velocity model fits the low wavenumber trend of the well log data. A subsequent run of conventional FWI is performed starting from JFWI model, in order to improve the resolution of the velocity model. The results is able to introduce higher wavenumber content to the velocity model, producing satisfactory fit with the observed data, and matching the well log data.
SummaryIt is well known that nonlinear site effects may arise in soils during strong ground motion. This translates into a decrease in propagation velocity, shift of resonance frequencies, increased material damping, and lessened ground motion amplification. In this study, we introduce a time-frequency resonance analysis (TFRA) technique to unveil nonlinear site response by computing broadband resonance frequencies derived from waveforms recorded across a wide range of ground motions at 567 stations of the Kiban Kyoshin network (KiK-net) in Japan. The found resonance frequencies follow closely those computed from surface to borehole spectral ratios. Furthermore, we quantify the coseismic frequency changes, which shift towards lower values as the earthquake ground shaking increases. At some stations, the extracted resonance frequencies attain up to a 60% decrease, representing a shear modulus reduction (μ/μmax) of 0.16 (84% decrease) assuming a homogeneous layer over a halfspace model. To ensure independence from specific seismic events, we establish peak ground acceleration (PGA) thresholds corresponding to 5% and 10% frequency shifts to identify regions where sites are prone to soil nonlinearity. We find that for a 5% frequency shift, some sites require a relatively small PGA (∼ 30 cm/s2) to trigger this effect, with most places needing a PGA ∼ 50 cm/s2. Furthermore, the computed μ/μmax values are categorized by the time-averaged shear-wave velocity to a depth of 30 and 5 meters (VS30 and VS05), which are proxies commonly used in earthquake engineering studies for characterizing site effects. We do not observe a clear correlation between the time-averaged shear-wave velocity to a certain depth and the computed shear modulus reduction (nonlinear site effect). Furthermore, no evident correlation was found between the nonlinear site effect and the earthquake magnitude, the distance from the earthquake to the site. This study suggests that nonlinear soil behavior is site-specific. This complicates the use of proxies or equations to take into account these effects, making it difficult to include soil nonlinearity in regional seismic hazard studies.
Publication date: Available online 4 March 2025
Source: Advances in Space Research
Author(s): Zihan Sun, Yiduo Quan, Naigang Hu, Na Li, Yiqun Zhang
Publication date: Available online 4 March 2025
Source: Advances in Space Research
Author(s): V.V. Demyanov, E.I. Danilchuk, Baocheng Zhang, D.Venkata Ratnam, Y.V. Yasyukevich
Publication date: Available online 4 March 2025
Source: Advances in Space Research
Author(s): Mahdi Momeni, Yenca Migoya-Orué
Publication date: Available online 4 March 2025
Source: Advances in Space Research
Author(s): Jun Tang, Lang Xu, Chaoqian Xu, Liang Zhang
With sea traffic set to rise in a warming Arctic, researchers are helping sailors plot a safer course through sea ice and icebergs thanks to more reliable satellite-based forecasts.
A new analysis of earthquake rupture directivity provides essential insights for seismic hazard and risk assessments in urban areas, particularly concerning the Main Marmara Fault near Istanbul in western Türkiye.
Hydrology experts at Flinders University are calling for urgent investigations into the operation of bore-fields that access fresh groundwater on Pacific islands, including Kiribati, where rising sea levels are already putting local water supplies at risk.
Author(s): N. I. Petrov
Lightning is a source of x-ray and gamma radiation, one of the most powerful natural photon emissions on Earth. In the paper, based on recently published measurement data, we explain the experimental results and state that the observed high-energy radiation is generated by synchrotron and cyclotron …
[Phys. Rev. E 111, 035205] Published Fri Mar 14, 2025
