The research examined transmission tower systems as a coupled ice-earthquake problem rather than evaluating icing and earthquakes only as separate hazards. This focus addresses a gap identified by the authors in earlier work, which often concentrated on single-hazard scenarios. The analysis considered how ice density and the type of ground motion affect the nonlinear response and seismic fragility of transmission towers. Earthquake recordings were obtained from the Turkish Accelerometric Database and Analysis System, providing a strong-motion data set for the probabilistic evaluation.

Particular attention was given to pulse-like and long-period ground motions, two motion characteristics that the study compared with more general ground motions. These records were used to examine whether the dynamic response of iced towers depended not merely on earthquake intensity but also on the nature of the shaking. The study combined ground-motion information with structural analysis and damage assessment to evaluate how ice accretion alters the seismic behavior of transmission tower systems.

Damage patterns varied with both ice density and ground-motion type. Higher ice density correlated with more significant structural damage, particularly in the study’s Rare Earthquake scenarios. The effect of motion type was intensity-dependent: during high-intensity earthquakes, the probability of damage to ice-covered towers was significantly higher under pulse-like and long-period ground motions than under general ground motions. The reported amplification is therefore associated with the combined loading condition analyzed by the model, while the damage analysis shows that records with different dynamic characteristics can produce markedly different outcomes for iced structures.

These findings come from model-based structural and probabilistic analyses using the selected strong-motion records, rather than from observations of a specific tower collapse or a direct survey of damaged transmission infrastructure. The study does not establish the frequency with which damaging ice-earthquake combinations occur in the field, and it does not report field measurements of a particular failure. Its scope is instead the dynamic response, damage patterns and seismic fragility of transmission towers under coupled ice-covered and earthquake action. The authors present the results as theoretical and data-based support for designing transmission towers with higher seismic performance and for controlling safety risks in extreme conditions where icing and strong shaking may occur together.

Subject of Research: Seismic fragility of transmission towers under coupled ice and earthquake loading

Article Title: Seismic evaluation of transmission tower structures under coupled ice-earthquake action

Article References: Fang, D., Liu, S., Sun, W., & Wang, H. (2026). Seismic evaluation of transmission tower structures under coupled ice-earthquake action. Natural Hazards, 122(22), Article 690. https://doi.org/10.1007/s11069-026-08472-4

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08472-4

Keywords: transmission towers, ice accretion, earthquake hazards, ground motion, seismic fragility, structural dynamics, Türkiye, pulse-like motion, long-period motion, Seismic, evaluation, transmission

The technique behind the service, Interferometric Synthetic Aperture Radar, or InSAR, is elegant in principle. A satellite emits radar pulses toward the ground and records the phase of the reflected signal, which is proportional to the two-way travel distance between the sensor and the surface. By comparing the phase of two images acquired at different times, researchers can measure tiny changes in that distance along the satellite’s line of sight. Individual comparisons, called interferograms, are noisy on their own, but combining many of them yields cumulative displacement time series capable of revealing movements of just a few millimeters per year.

Applying this method in Svalbard, however, is far from straightforward. Snow cover causes the radar phase signal to decorrelate, so the team processed only images from snow-free periods, typically spanning June to October and, in favorable years, from late May to early December. The cold climate and perennially frozen ground produce heterogeneous, nonlinear deformation patterns that demand processing strategies different from those used for temperate mainland services such as InSAR Norway or the European Ground Motion Service, neither of which covers the archipelago. The result is a dataset tailored to permafrost terrain, something that has been lacking despite a growing body of smaller InSAR case studies in polar regions.

The service covers five study areas on Spitsbergen Island: Longyearbyen, Ny-Ålesund, Svea, Hornsund and Kapp Linné. These locations were chosen for their societal and scientific significance, hosting the main Norwegian settlements, research stations, tourist destinations and cultural heritage sites. Roughly sixty percent of Svalbard is glaciated, and most of the remaining terrain sits on permafrost beneath an active layer that freezes and thaws each year. Because the archipelago is among the fastest-warming Arctic regions, permafrost temperatures and active layer thickness are increasing, driving more frequent and faster mass movements as well as long-term subsidence from melting ground ice.

Technically, the products derive from Sentinel-1 C-band radar imagery at a wavelength of about 5.6 centimeters, acquired in the Interferometric Wide swath mode from both ascending and descending orbital geometries. The team applied a spatial multi-looking factor of 8 by 2 pixels, producing a ground resolution of roughly 30 meters, with temporal resolution matching the satellite revisit interval of 6 to 12 days depending on the period. The processing chain included removal of orbital and topographic phase components, filtering to suppress speckle and atmospheric effects, phase calibration, interferogram unwrapping and geocoding, all built around a Distributed Scatterer approach based on the Small Baseline Subset algorithm, which combines partially overlapping interferograms to increase redundancy and reduce noise.

Two complementary product types capture ground dynamics at different timescales. Seasonal products document cumulative short-term displacements within each snow-free period, using image pairs separated by 6 to 48 days, with time series spanning 2016 to 2024 for the ascending geometry and 2018 to 2024 for the descending geometry. These products are suited to identifying rapid changes of up to a couple of decimeters within a single season, such as active layer dynamics or slope movement. Interannual products, by contrast, use image pairs separated by roughly one year and document slow, gradual displacement trends of up to a few centimeters per year, such as subsidence from permafrost degradation or downslope creep.

The scientific payoff is already visible in the results. On slopes, the magnitude of maximum seasonal displacements varies with the rich diversity of periglacial landforms, including solifluction sheets, rock glaciers, rock slope instabilities and debris-covered glaciers, allowing regional-scale mapping of their distribution and kinematics. In flat, sediment-filled valley bottoms, the cyclic subsidence and heave patterns recorded during thawing and refreezing of the active layer vary with sediment frost susceptibility, offering a proxy for mapping ground ice content. The timing of the transition from subsidence to heave even provides an indicator of seasonal freeze-onset in years with little autumn snow cover.

The interannual products add another dimension. In lowland coastal areas, they reveal long-term subsidence likely caused by melting ice at the top of the permafrost, and the time series allow researchers to distinguish areas with relatively linear trends from those showing accelerating or decelerating movement. Fast-moving features such as rock glaciers tend to decorrelate over the long intervals used for interannual pairs, but slower phenomena like solifluction are well captured. Together, the two product families support geohazard assessment, land-use planning, infrastructure management and the protection of cultural heritage sites, while also serving as potential climate change indicators, since ground dynamics respond directly to environmental drivers.

The service was designed with users in mind from the start. Over a three-year development phase funded by the Norwegian Space Agency and the Geological Survey of Norway, the team held workshops and surveys involving stakeholders including the Governor of Svalbard, the Longyearbyen Community Council, the Norwegian Polar Institute and the University Centre in Svalbard, shaping product specifications around real operational needs. The results are freely accessible through a web-based visualisation tool at svalbard.insar.no, released in February 2026, and distributed as CSV files via the Zenodo repository, making the data usable by everyone from polar researchers to local planners.

Looking ahead, the team intends InSAR Svalbard as a long-term service rather than a static release, with regular updates as new Sentinel-1 images arrive and plans to expand coverage toward the full archipelago. Future data sources may include L-band radar from the NASA-ISRO NISAR mission and ESA’s upcoming ROSE-L mission, expected no earlier than 2028, which could improve signal stability over complex surfaces and capture faster-moving processes, though coverage and schedule limitations mean alternatives must still be explored. The researchers hope the platform will set a baseline for similar services across the polar north, potentially evolving into a pan-Arctic ground motion service designed for cold-climate conditions, a capability that existing continental services, built for temperate terrain, cannot yet provide.

Subject of Research: Satellite InSAR monitoring of surface displacement and permafrost dynamics in Svalbard

Article Title: Brief communication: InSAR Svalbard Ground Motion Service – observing surface displacements in the High Arctic

Article References: Bredal, M., Rouyet, L., Wendt, L., Hindberg, H., Stødle, D., Lauknes, T. R., van Oostveen, J., Larsen, Y., Aslan, G., Hauglin, E., Dehls, J., Sundal, A., Odh, A., & Moldestad, D. A. (2026). Brief communication: InSAR Svalbard Ground Motion Service – observing surface displacements in the High Arctic. Earth Observation, 1(1), 121-128. https://doi.org/10.5194/eo-1-121-2026

Image Credits: AI Generated

DOI: 10.5194/eo-1-121-2026

Keywords: InSAR, Svalbard, permafrost, Sentinel-1, ground motion, remote sensing, Arctic, geohazards, thaw subsidence, frost heave, radar interferometry, climate change

The research focuses on so-called coherency functions, statistical tools that quantify how strongly ground motions at two separated points on the ground surface are correlated as a function of frequency and distance. When waves propagate through the heterogeneous Earth, scattering, differences in arrival times known as wave passage effects, and local site conditions all erode this correlation, particularly at high frequencies. Because engineers cannot know the exact ground motion at every foundation point in advance, they rely on empirical coherency models fitted to dense instrument arrays, such as the SMART-1 array in Taiwan and the Lotung large-scale seismic experiment, to generate statistically consistent sets of spatially varying ground motion time histories for analysis.

A central motivation of the study is to validate the spectral correction factors recommended in ASCE Standard 4-98, the American Society of Civil Engineers standard for the seismic analysis of safety-related nuclear structures, and the coherency model developed by Norman Abrahamson in 2005 for the Electric Power Research Institute. These corrections account for the fact that the motion actually experienced by a large foundation is smoother, and generally weaker at high frequencies, than the free-field motion recorded in the soil away from the structure. This averaging effect, sometimes called the foundation input motion reduction, depends on the size and stiffness of the foundation, the properties of the underlying soil, and the assumed degree of incoherency in the incoming wave field.

To carry out the investigation, the team implemented several widely used coherency functions in code_aster, the open-source finite element software developed by EDF for advanced structural analysis. The models compared include classical formulations such as the Harichandran-Vanmarcke model, the Hao-Oliveira-Penzien model, the Der Kiureghian model and the Abrahamson and co-workers empirical functions derived from the Lotung experiment. Using these functions, the researchers generated ensembles of spatially varying ground motions compatible with target free-field response spectra for both rock and soil site profiles, following established simulation techniques for multivariate stochastic processes.

In the first part of the study, the authors analysed a rigid square foundation subjected to spatially varying ground motion that includes wave incoherency. From the computed foundation motions they derived foundation response spectra, which describe the maximum response a single-degree-of-freedom oscillator would experience at the base of the structure. By comparing these spectra with the corresponding free-field response spectra, they determined reduction factors, that is, ratios quantifying how much the foundation motion is attenuated relative to the free field at each frequency. These numerically derived factors were then benchmarked against the spectral corrections prescribed in the EPRI 2005 methodology and ASCE Standard 4-98.

The results reveal a striking sensitivity: the foundation response spectra can change considerably depending on which coherency model and which ground motion parameters are assumed. Because each empirical model was calibrated on different arrays, site conditions and frequency ranges, they do not produce identical descriptions of the wave field, and these differences propagate directly into the computed reduction factors. For practitioners, this means that the choice of incoherency model is not a technical detail but a decision that can materially influence the seismic demand calculated for safety-critical structures, particularly in the frequency range above a few hertz where incoherency effects are strongest.

The second part of the paper extends the analysis to a full reactor building of a nuclear power plant, coupling the spatially varying excitation with a soil-structure interaction model. Soil-structure interaction refers to the mutual influence between the flexibility of the supporting soil and the dynamic response of the structure: soft soils can lengthen the effective period of the building system and dissipate energy through radiation damping, while the massive foundation filters and averages the incoming wave field. When the ground motion is also spatially incoherent, these two mechanisms interact, and the resulting structural response can differ substantially from what a conventional analysis with identical motion at all support points would predict.

The findings show that the effect of incoherency is remarkable for secondary systems within the reactor building that are sensitive to frequencies larger than 10 hertz. Secondary systems include piping, cable trays, equipment and other components anchored to the structure, whose response is governed by the floor motion spectra at their attachment points rather than by the ground motion itself. Because incoherency predominantly suppresses high-frequency content in the foundation input motion, floor response spectra at these higher frequencies can be reduced, which may ease the design burden for high-frequency equipment, but the magnitude of this reduction depends again on the coherency model selected.

The work was carried out within an international collaborative framework, with support from the German Academic Exchange Service (DAAD), the European Commission’s METIS program under Horizon 2020, and the German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection through the CRUAS-19 project. This combination of academic and industrial partners reflects the practical stakes of the research: nuclear regulators and operators in Europe and elsewhere are increasingly requiring that wave incoherency be explicitly accounted for in site-specific seismic assessments, and reliable, validated modelling tools are essential for that task.

For the earthquake engineering community, the study delivers a clear message about uncertainty and standardisation. The spectral corrections embedded in ASCE Standard 4-98 and the EPRI methodology represent decades of accumulated empirical knowledge, but the new results show that they should be applied with an awareness of the sensitivity of the outcome to the underlying coherency assumptions. As dense seismic arrays continue to record data worldwide, and as site-specific coherency functions are developed for individual nuclear sites, the authors’ open-source implementation in code_aster offers a transparent pathway for engineers to test alternative models, quantify the spread of predicted foundation and floor response spectra, and ultimately make more robust safety decisions for the large semi-rigid structures that society depends upon most.

Subject of Research: Effect of spatial ground motion coherency models on soil-structure interaction analysis of large semi-rigid structures such as nuclear reactor buildings

Article Title: Influence of different spatial coherency models in soil-structure interaction analyses of large semi-rigid structures

Article References: Soyluk, K., Zouatine, M., Sadegh-Azar, H., Zentner, I., Kudawoo, D., & Khemakhem, A. (2026). Influence of different spatial coherency models in soil-structure interaction analyses of large semi-rigid structures. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02664-w

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02664-w

Keywords: spatial variability, soil-structure interaction, coherency model, nuclear power plant, reactor building, seismic analysis, ground motion, wave incoherency, foundation response spectra, ASCE Standard 4-98, code_aster, earthquake engineering