My purpose in this commentary is to provide further context to Christensen (2026) in this issue of Seismica in order to fill some gaps so that readers better understand how the measurements are made, know what the analyses are based on, and know where the pitfalls in employing these results might lie. My experiences in reviewing and editing have revealed that many papers that focus on elastic or seismic anisotropy err as they are written often without understanding the basic principles. This problem is aggravated because some modern methods, such as Electron Backscatter Diffraction (EBSD), have made calculation of the anisotropy of metamorphic rocks readily accessible and production of figures perhaps too easy. I hope to both amplify and clarify the results archived in Christensen (2026) so they are not similarly misused and to provide readers with some tutorial background and more in-depth sources in order that they can avoid overinterpretation of anisotropy results more generally.
<p>The Normalized Difference Vegetation Index (NDVI) can be effectively used for monitoring the spatial and temporal dynamics of riparian vegetation. However, quantitative and efficient evaluations of the links between NDVI and bio-hydromorphological processes remain limited, particularly in river management contexts where dense in-channel vegetation can obstruct flow and reduce conveyance capacity. Using 200 cloud-free Sentinel-2 images (2015–2024) covering a 20-km reach of the Chikuma River (Japan), we evaluated the utility of high temporal resolution NDVI and greenness index (defined as NDVI <span class="inline-formula">></span> 0.2) as quantitative indicators of bio-hydromorphological dynamics and its implications for riverine management. The analysis focused on the relationships between NDVI dynamics, flood magnitude, relative elevation along lateral channel morphology, and seasonal vegetation variability within a frequently disturbed channel. The results show that NDVI fluctuations strongly correspond to flood disturbances at lower relative elevations, whereas vegetation at higher elevations remains relatively stable. The annual maximum greenness ratio was well described by a logistic model along the cross-sectional transects. Annual greenness ratio exhibited clear seasonal patterns, showing a late-summer (August–September) greenness peak. These spatiotemporal and seasonal NDVI characteristics demonstrate the potential of Sentinel-2 imagery to operationalize both the “when” (timing) of vegetation management and the “where” (priority zones defined by relative elevation), providing a transferable, remotely sensed basis for flood-risk mitigation in frequently disturbed riverine environments.</p>
Andres Felipe Peña Castro, Brandon Schmandt, Margaret Glasgow
et al.
Accurate estimation of earthquake source parameters—such as moment magnitudes, corner frequencies, and stress drops—is essential for improving seismic hazard assessments and understanding earthquake physics. In this study, moment magnitudes (MW) are calculated for 31,581 earthquakes associated with wastewater injection in the Raton Basin (located along the border between northern New Mexico and southern Colorado) between 2016 and 2024 using radiative transfer theory to fit coda decay envelopes. Our results show that it is feasible to estimate moment magnitudes down to MW ~1 with coda envelopes from a small local monitoring network. Significant differences were found between MW and local magnitudes (ML) for small earthquakes (M < 3.0). A linear relationship was optimized to convert ML to MW: MW = 0.7ML + 0.96 and MW = 0.73 ML + 0.99 (for the events reported by the U.S. Geological Survey), which can be applied in future studies of Raton Basin seismicity. We find that b-values calculated employing different methods and using ML are approximately 1.0, while those using MW range from 1.2 to 1.4. A larger estimate of the b-value could influence interpretations of the statistical behavior of earthquakes associated with injection and consequently seismic hazard assessments based on a magnitude–frequency distribution. The potential differences between local versus moment magnitude-based earthquake statistics should be considered in other seismically active regions.
<p>This study investigated the computational benefits of using multi-fidelity statistical estimation (MFSE) algorithms to quantify uncertainty in the mass change of Humboldt Glacier, Greenland, between 2007 and 2100 using a single climate change scenario. The goal of this study was to determine whether MFSE can use multiple models of varying cost and accuracy to reduce the computational cost of estimating the mean and variance of the projected mass change of a glacier. The problem size and complexity were chosen to reflect the challenges posed by future continental-scale studies while still facilitating a computationally feasible investigation of MFSE methods. When quantifying uncertainty introduced by a high-dimensional parameterization of the basal friction field, MFSE was able to reduce the mean-squared error in the estimates of the statistics by well over an order of magnitude when compared to a single-fidelity approach that only used the highest-fidelity model. This significant reduction in computational cost was achieved despite the low-fidelity models used being incapable of capturing the local features of the ice-flow fields predicted by the high-fidelity model. The MFSE algorithms were able to effectively leverage the high correlation between each model's predictions of mass change, which all responded similarly to perturbations in the model inputs. Consequently, our results suggest that MFSE could be highly useful for reducing the cost of computing continental-scale probabilistic projections of sea-level rise due to ice-sheet mass change.</p>
<p>Studies of Earth rotation variations generally assume that changes in non-tidal oceanic angular momentum (OAM) manifest the ocean's direct response to atmospheric forces. However, fluctuations in OAM may also arise from chaotic intrinsic ocean processes that originate in local nonlinear (e.g., mesoscale) dynamics and can map into motions and mass variations at basin scales. To examine whether such random mass redistributions effectively excite polar motion, we compute monthly OAM anomalies from a 50-member ensemble of eddy-permitting global ocean/sea ice simulations that sample intrinsic variability through a perturbation approach on model initial conditions. The resulting OAM (i.e., excitation) functions, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mover accent="true"><mi mathvariant="italic">χ</mi><mo stretchy="false" mathvariant="normal">^</mo></mover><mi mathvariant="normal">O</mi></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="4209a2ebd874764d16b60e77545a25e3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-16-75-2025-ie00001.svg" width="16pt" height="15pt" src="esd-16-75-2025-ie00001.png"/></svg:svg></span></span>, are examined for their spread, spectral content, and role in the polar motion excitation budget from 1995 to 2015. We find that intrinsic <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mover accent="true"><mi mathvariant="italic">χ</mi><mo stretchy="false" mathvariant="normal">^</mo></mover><mi mathvariant="normal">O</mi></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="5a07498b9a02c6f507300fc609dd0ab6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-16-75-2025-ie00002.svg" width="16pt" height="15pt" src="esd-16-75-2025-ie00002.png"/></svg:svg></span></span> signals are comparable in magnitude to the forced component at all resolved periods except the seasonal band, amounting to <span class="inline-formula">∼</span> 46 % of the total oceanic excitation (in terms of standard deviation) on interannual timescales. More than half of the variance in the intrinsic mass term contribution to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mover accent="true"><mi mathvariant="italic">χ</mi><mo stretchy="false" mathvariant="normal">^</mo></mover><mi mathvariant="normal">O</mi></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="b692688346d4fcfacee2f6152b71e819"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-16-75-2025-ie00003.svg" width="16pt" height="15pt" src="esd-16-75-2025-ie00003.png"/></svg:svg></span></span> is associated with a single global mode of random bottom pressure variability, likely generated by nonlinear dynamics in the Drake Passage. Comparisons of observed interannual polar motion excitation against the sum of known surficial mass redistribution effects are sensitive to the representation of intrinsic <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mover accent="true"><mi mathvariant="italic">χ</mi><mo stretchy="false" mathvariant="normal">^</mo></mover><mi mathvariant="normal">O</mi></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="0f3a73f3fbed0a489e998628e7d4569c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-16-75-2025-ie00004.svg" width="16pt" height="15pt" src="esd-16-75-2025-ie00004.png"/></svg:svg></span></span> signals: reductions in the observed excitation variance can be as high as 68 % or as low as 50 % depending on the choice of the ensemble member. Chaotic oceanic excitation thus emerges as a new factor to consider when interpreting low-frequency polar motion changes in terms of core–mantle interactions or employing forward-modeled OAM estimates for Earth rotation predictions.</p>
<p>Climate change metrics result from analytical simplification of complex and diverse climate models that are generally not deeply investigated by Life Cycle Assessment communities. We investigated the Sixth Assessment Report of the Intergovernmental Panel on Climate Change to properly gather updated metric equations, climate parameters and associated uncertainties. Metrics are mainly designed with a single gas pulse emission at <span class="inline-formula"><i>t</i><sub>0</sub></span> whereas multi-gas and multi-time pulse emissions are mostly encountered in LCA modelling. Therefore, common static and relative metrics might not suit dynamic climate change assessments (dCCA) that differentiate pulse timing and gas contributions over time. This study focuses on absolute and dynamic metrics – cumulative radiative forcing (AGWP or <span class="inline-formula">Δ<i>F</i></span>) and global temperature change (AGTP or <span class="inline-formula">Δ<i>T</i></span>) – applied to well-mixed greenhouse gases. Cumulative radiative forcing assessment at 20, 100, 500 years appears sufficient. Global temperature change metrics have some advantages that offset their higher uncertainties. (1) Degree Celsius unit better suits peak warming targets. (2) Positive and negative peaks, as well as long-term temperature change, partly alleviate the time horizon decision issue while assessing product systems. (3) Graphical representations are comparable to simultaneously depict short- and long-lived climate forcers. In future assessment reports, IPCC is invited to recall climate equations and updated parameters values in a pedagogical way and to adopt peak and long-term temperature change metrics. dCCA recommendations are to plot <span class="inline-formula">Δ<i>F</i></span> and <span class="inline-formula">Δ<i>T</i></span> temporal profiles of product systems up to 600 years and use suggested metrics. This should enable going towards climate neutrality with more clarity, transparency and understanding.</p>
<p>Increasing evidence highlights the disruptive effects of compound climate extremes on global crop yields under climate change. Existing studies predominantly rely on the whole growing–season scale and relative thresholds, and limit the ability to capture crop physiological sensitivities and yield responses that vary critically across growth stages. Here, we analyzed the spatiotemporal variations, dominant drivers, and potential impacts on the yields of concurrent heat–drought and chilling–rain events for single– and late–rice in southern China from 1981 to 2018. Specifically, we carefully distinguished three sensitive growth stages of rice and stage–specific climate stress types and thresholds based on rice physiology. Temporally, single–rice experienced a significant increase in concurrent heat–drought events, while late–rice experienced a modest rise in chilling–rain events. Spatially, the hotspots of concurrent heat–drought events varied greatly across the three growth stages. These spatial patterns are driven primarily by differences in crop phenology across locations, rather than by the occurrence of extreme climate conditions. The concurrent chilling–rain events of late–rice were widespread within the planting regions, with a higher incidence in certain areas. Path analysis identified heat stress as the primary driver of heat–drought impacts (particularly in jointing–booting and heading–flowering stages), whereas chilling and rain stress exerted comparable effects for late–rice. Our assessment of compound event impacts and sensitivity on rice yield revealed significant growth–stage differences, with comparable yield losses from both concurrent heat–drought and chilling–rain events. Single–rice showed the highest sensitivity to heat–drought events during the grain filling stage, whereas the late–rice exhibited greater sensitivity during the heading–flowering stage. The historical impact on yield diverged markedly across growth stages, with the largest having occurred in the grain filling stage, particularly for heat–drought events. Our study provided important information on compound agroclimatic extremes, in the context of southern China's rice production system, and the results provide important information for risk management and adaptation strategies under climate change.</p>
Studying the spatial response of a single-axis magnetometer could be the key parameter to optimize the ultimate performances of magnetic heads of detection. Indeed, the problem of non-orthogonality, misalignment, and 3D spatial response could be improved based on the knowledge of the 3D sensor spatial response. In that way, we have investigated the latter for our giant magneto-impedance (GMI) magnetometer, as a far-field pattern, by using a three-axis Helmholtz coil system. Firstly, we calibrate our device and secondly, we apply a specific 3D magnetic field to obtain this pattern. The latter helps to observe the directional or angular dependence of the sensor sensitivity versus the applied magnetic field, as we exemplified. The results confirm the excellent directivity of our off-diagonal GMI magnetometer. The evaluation of the associated error compared to an ideal vector magnetometer is also given and discussed.
Theoretical calculations of the temperature-dependent magnetization in FeGd alloys were done with the use of Heisenberg-type atomistic spin Hamiltonian and Monte Carlo algorithms. The random allocation of atoms in the desired crystal structure was used for simulations of magnetically amorphous alloys. Performed calculations for the two different crystal structures have shown an important role of coordination number on the observed critical temperature and compensation point. Moreover, the value of the exchange interaction between Fe and Gd sublattices plays a key role in the simulations—an increase in the Fe–Gd exchange constant provides an increase in critical temperature for each concentration of elements, which explains the higher temperature stabilization of Gd moments. It was shown that obtained temperature-dependent magnetization behavior is consistent with experimental observations, which confirms the applicability of the atomic model used to study FeGd or other magnetic alloy structures.
<p>Rock slope failures in the Lake District, UK, have been associated with deglacial processes after the Last Glacial Maximum, but the controls and timing of the failures remain poorly known. A cirque headwall failure was investigated to determine failure mechanisms and timing. The translated wedge of rock is thin and lies on a steep failure plane, yet the friable strata were not disrupted by downslope movement. Fault lines and a failure surface, defining the wedge, were used as input to a numerical model of rock wedge stability. Various failure scenarios indicated that the slope was unstable and would have failed catastrophically if not supported by glacial ice in the base of the cirque. The amount of ice required to buttress the slope is insubstantial, indicating likely failure during the thinning of the cirque glacier. We propose that, as the ice thinned, the wedge was lowered slowly down the cirque headwall, gradually exposing the failure plane. A cosmogenic <span class="inline-formula"><sup>10</sup></span>Be surface exposure age of <span class="inline-formula">18.0±1.2</span> ka from the outer surface of the wedge indicates Late Devensian de-icing of the backwall of the cirque, with a second exposure age from the upper portion of the failure plane yielding <span class="inline-formula">12.0±0.8</span> ka. The <span class="inline-formula">18.0±1.2</span> ka date is consistent with a small buttressing ice mass being present in the cirque at the time of regional deglaciation. The exposure age of <span class="inline-formula">12.0±0.8</span> ka represents a minimum age, as the highly fractured surface of the failure plane has experienced post-failure mass-wasting. Considering the chronology, it appears unlikely that the cirque was reoccupied by a substantial ice mass during the Younger Dryas stadial.</p>
Vertical motions, especially in the active continental margins such as Kuril-Kamchatka transition zone, are still pure studied. One of the factors significantly affecting the amplitudes and directions of vertical motions is mantle convections. Estimates of the amplitudes of vertical motions in region have been obtained by means of numerical modeling of the mantle convection made by the method of finite elements. The values of emergences in the area of Sakhalin Island and the Kuril Ridge from 0–3 to 13 m were obtained with the accepted rates of mantle convection from 1 to 5 mm/year. The results obtained should be taken into account when reconstructing neotectonic history of the region and assessing the geodynamic situation in the region of the Sea of Okhotsk.
<p>Depressions – inwardly draining regions – are common to many landscapes. When there is sufficient moisture, depressions take the form of lakes and wetlands; otherwise, they may be dry. Hydrological flow models used in geomorphology, hydrology, planetary science, soil and water conservation, and other fields often eliminate depressions through filling or breaching; however, this can produce unrealistic results. Models that retain depressions, on the other hand, are often undesirably expensive to run. In previous work we began to address this by developing a depression hierarchy data structure to capture the full topographic complexity of depressions in a region. Here, we extend this work by presenting the Fill–Spill–Merge algorithm that utilizes our depression hierarchy data structure to rapidly process and distribute runoff. Runoff fills depressions, which then overflow and spill into their neighbors. If both a depression and its neighbor fill, they merge. We provide a detailed explanation of the algorithm and results from two sample study areas. In these case studies, the algorithm runs 90–2600 times faster (with a reduction in compute time of 2000–63 000 times) than the commonly used Jacobi iteration and produces a more accurate output. Complete, well-commented, open-source code with 97 % test coverage is available on GitHub and Zenodo.</p>
J. J. Lindsay, H. S. R. Hughes, C. M. Yeomans
et al.
Large Igneous Provinces, and by extension the mantle plumes that generate them, are frequently associated with platinum-group element (PGE) ore deposits, yet the processes controlling the metal budget in plume-derived magmas remains debated. In this paper, we present a new whole-rock geochemical data set from the 135 Ma Paraná-Etendeka Large Igneous Province (PELIP) in the South Atlantic, which includes major and trace elements, PGE, and Au concentrations for onshore and offshore lavas from different developmental stages in the province, which underwent significant syn-magmatic continental rifting from 134 Ma onwards. The PELIP presents an opportunity to observe magma geochemistry as the continent and sub-continental lithospheric mantle (SCLM) are progressively removed from a melting environment. Here, we use an unsupervised machine learning approach (featuring the PCA, t-SNE and k-means clustering algorithms) to investigate the geochemistry of a set of (primarily basaltic) onshore and offshore PELIP lavas. We test the hypothesis that plume-derived magmas can scavenge precious metals including PGE from the SCLM and explore how metal concentrations might change the metal content in intraplate magmas throughout rifting. Onshore lavas on the Etendeka side of the PELIP are classified as the products of deep partial melts of the mantle below the African craton but without significant PGE enrichment. Offshore lavas on both continents exhibit similarities through the multi-element space to their onshore equivalents, but they again lack PGE enrichment. Of the four onshore lava types on the Paraná side of the PELIP, the Type 1 (Southern) and Type 1 (Central-Northern) localities exhibit separate PGE-enriched assemblages (Ir-Ru-Rh and Pd-Au-Cu, respectively). It follows that there is a significant asymmetry to the metallogenic character of the PELIP, with enrichment focused specifically on lavas from the South American continent edge in Paraná. This asymmetry contrasts with the North Atlantic Igneous Province (NAIP), a similar geodynamic environment in which continent-edge lavas are also PGE-enriched, albeit on both sides of the plume-rift system. We conclude that, given the similarities in PGE studies of plume-rift environments, SCLM incorporation under progressively shallowing (i.e., rifting) asthenospheric conditions promotes the acquisition of metasomatic and residual PGE-bearing minerals, boosting the magma metal budget.