Land subsidence is a global threat. In Europe, it impacts tens of millions of people by increasing flood risk and damage to the built environment. Land subsidence is the result of a combination of natural and human-induced subsurface processes, and there is considerable potential to mitigate the human-induced drivers through policy and legislation. We show how Europe is approaching the issues of measuring and addressing subsidence at a continental scale. We look ahead to the challenges of climate change and the energy transition in the context of amplifying the impacts of land subsidence, providing lessons learned from the European approach. Millions of people are impacted by land subsidence, which is accelerated by human-induced drivers. Across Europe, research and policy is focused on managing these drivers and mitigating their influence, with data and monitoring infrastructure playing a key role in tackling future challenges.

The Urban Geo-climate Footprint (UGF) project has been developed in the context of the Urban Geology Expert Group of Euro Geo Surveys, aimed to define a new methodology to classify and cluster cities by geological and climatic point of view. The basic assumption of the UGF approach is that cities with similar geological-geographical settings should have similar challenges to manage, due to both common geological issues and climate change subsoil-related effects. Following this approach, a holistic tool consisting in a complex spreadsheet has been developed and applied to more than 40 European cities, in collaboration with several Geological Surveys of Europe. It is demonstrated as the Urban Geo-climate Footprint tool is currently capable of providing a semi-quantitative quick representation of the pressures driven by geological and climatic complexity in the analysed cities, providing for the first time such classification for the urban environment. Through the wide application of this methodology several benefits could be reached as the general awareness increase of non-experts and the enhanced reading-the-landscape capacity of decision makers about the link between geological setting and the increase in pressures due to climate change and anthropogenic activity. Furthermore, the UGF approach would facilitate the possibility to exchange best practices among similar cities for planning purposes, and it would support the decision processes to define and differentiate policies and actions, also supporting policy and cooperative geoscience and climate justice.

At present, worldwide population and economic expansion boosts the demand for environmental resources and urban development. According to the 2022 United Nations World Population Prospect, the global population may reach up to 9.7 billion people by 2050 of which nearly 70% will be residing in urban areas. As a result, the urban setting will become increasingly complex and with more geological and climate negative effects exacerbated by the increasing population, the unequal distribution of economic and energy resources, and the over-exploitation of the environment.To face these worldwide issues, a global approach to knowledge is required with concerted actions by all countries and cities. One possible solution addressing this need could be achieved firstly by classifying cities throughout the world as complex systems defined by geological, subsoil-related climate impact, environmental, and anthropic factors considered in a more holistic way.To achieve this objective, the Urban Geo-climate Footprint (UGF) project, aimed to define a new methodology to classify and cluster cities by geological and climatic point of view.The basic assumption of the UGF approach is that cities with similar geological-geographical settings should have similar challenges to manage, due to both common geological issues and climate change subsoil-related effects. Following this approach, a holistic tool consisting in a complex spreadsheet has been developed and applied to several European cities, in collaboration with several Geological Surveys of Europe.It is demonstrated as the Urban Geo-climate Footprint tool is currently capable of providing a semi-quantitative quick representation of the pressures driven by geological and climatic complexity in the analysed cities, providing for the first time such classification for the urban environment.Through the wide application of this methodology several benefits could be reached as the general awareness increase of non-experts and the enhanced reading-the-landscape capacity of decision makers about the link between geological setting and the increase in pressures due to climate change and anthropogenic activity.Furthermore, the UGF approach would facilitate the possibility to exchange best practices among similar cities for planning purposes, and it would support the decision processes to define and differentiate policies and actions, also supporting policy and cooperative geoscience and climate justice.

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This study assesses hydrogeological hazards in the Saint-Vaast region, Belgium, impacted by three decades of deformation post-coal mine closure. Using Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) applied to 30 years of Synthetic Aperture Radar (SAR) data along with geological investigations and 13 years of piezometric well data, we analysed subsurface dynamics leading to environmental hazards in the region. We focused on identifying key periods of significant deformation pattern changes. The soft Wealden terrains (Lower Cretaceous) are characterized by alternating sandstones, clay, and sand facies, composing the sedimentary roof of an old mine drainage adit dug at 30 m depth. The presence of this mined adit structure is contributing to the current vulnerability of the region. Especially, when the abandoned mine drainage adit was filled with water following the cessation of pumping. Due to an increase in the water level in the Wealden aquifer below the gallery, natural groundwater flow paths and pressures have increased over time. At least two significant mudflow outbursts, in 2009 and 2018, occurred. This study shows that both events were correlated with changes in water level and deformation. Moreover, results suggest a new phase of rising water levels and ground uplift due to increased pressure in the Wealden aquifer. A crucial outcome of this research is the assessment of the potential for another similar incident soon, informed by the correlation analysis of water level and ground displacement time series.

Urban resilience is critical to allow cities to withstand the challenges of the 21st Century. One factor that is often overlooked in such assessments is the role of the subsurface. A novel methodology called the Urban Geo-climate Footprint (UGF) has been developed to classify cities quickly and comprehensively from geological and climatic perspectives. The method operates on the fundamental assumption that cities with similar geological-geographical settings will face similar challenges, due to both common geological issues and associated climate impacts. The UGF approach has been applied to 41 European cities in collaboration with 17 Geological Surveys of Europe, the results of the UGF analysis are presented along with a regional classification of the geological resilience indicators. The UGF tool provides a semi-quantitative representation of the pressures driven by geological and climatic complexity for the cities presented, providing for a first time such classification of the urban environment. The advantage of this methodology lies in increasing awareness among non-experts and decision-makers of the interplay between geological settings, climate change pressures, and anthropogenic activities. Furthermore, it facilitates the exchange best practices among city planners to increase resilience, supporting knowledge based decision making to promote actions and policies, that enhance geoscience-informed climate justice.

Interferometric Synthetic Aperture Radar (InSAR) technology has been used to detect the location and magnitude of ground deformation for the past 30 years, providing cost-effective measurements with a fine resolution and precision within centimeters under ideal conditions1. Persistent Scatterer InSAR Interferometry (PS-InSAR) is an InSAR algorithm that has been developed to overcome decorrelation due to changes in the physical characteristics of the surface over time that limit the InSAR applications 2,3.PS-InSAR processing has been used to identify multiple localized land subsidence in the Antwerp and Leuven areas in Belgium. In Antwerp, the harbour was gradually developed, leading to dock excavations in a compressible estuary polders environment and PS-InSAR was used to detect, map and study the ground displacements4. In Leuven, significant subsidence was observed through the city and the suburbs, potentially due to delayed consolidation in compressible, low permeability aquitards. One of the possible cause of these subsidence phenomena is related to variation in groundwater levels resulting in consolidation processes. To test this hypothesis, geomechanical calculations coupled to groundwater flow models are carried out to simulate the vertical displacements. The results are compared to PS-InSAR-derived subsidence observations for a better understanding of subsurface consolidation mechanisms.However, there are several practical and conceptual challenges that must be considered when comparing InSAR measurements to results from hydrogeological and geomechanical models. One issue is the choice of the appropriate modeling scale, as subsidence may occur locally but also regionally as influenced by groundwater pore pressure variations occurring at different scales. Another challenge lies in the selection of the appropriate conceptual assumptions linked to the groundwater flow and geomechanical models. Indeed, in addition, uncertainty in the model parameter values is a typical source of uncertainty in the model results. There may also be errors in the InSAR measurements due to various factors such as atmospheric effects and changes in the surface roughness. All these challenges must be taken into account when comparing InSAR measurements to model results.In conclusion, comparing InSAR measurements with hydrogeological and geomechanical modeling results can provide valuable insights into the actual mechanisms of subsidence. However, it is important to carefully consider the practical and conceptual challenges and limitations linked to this interesting comparison. References:1 Peng, M., Lu, Z., Zhao, C., Motagh, M., Bai, L., Conway, B. D., & Chen, H. (2022). Mapping land subsidence and aquifer system properties of the Willcox Basin, Arizona, from InSAR observations and independent component analysis. Remote Sensing of Environment, 271, 112894.2 Ferretti, A., Prati, C., & Rocca, F. (2000). Nonlinear subsidence rate estimation using permanent scatterers in differential SAR interferometry. IEEE Transactions on geoscience and remote sensing, 38(5), 2202-2212.3 Ferretti, A., Prati, C., & Rocca, F. (2001). Permanent scatterers in SAR interferometry. IEEE Transactions on geoscience and remote sensing, 39(1), 8-20.4 Declercq, P. Y., Gérard, P., Pirard, E., Walstra, J., & Devleeschouwer, X. (2021). Long-term subsidence monitoring of the Alluvial plain of the Scheldt river in Antwerp (Belgium) using radar interferometry. Remote Sensing, 13(6), 1160.

Spatio-temporal ground-movement measurements and mappings have been carried out in the Campine coalfield in Belgian Limburg since the closure of the mines to document post-mining effects. MT-InSAR measurements are compared to groundwater head changes in the overburden and to height data from the closest GNSS stations. Radar interferometry is used to estimate the extension and the velocity of ground movements. In particular, the MT-InSAR technique has been applied to SAR acquisitions of the satellites ERS-1/2 (1991–2005), ENVISAT (2003–2010), COSMO-SkyMed (2011–2014), and Sentinel-1A (2014–2022). The images were processed and used to highlight a switch from subsidence to uplift conditions in the western part of the coal basin, while the eastern part had already been affected by a rebound since the beginning of the ERS-1/2 acquisitions. Following the closure of the last active colliery of Zolder in 1992 and the subsequent cease of mine-water pumping, a recharge of mine-water aquifers occurred in the western part of the basin. This process provoked the change from subsidence to uplift conditions that was recorded during the ENVISAT period. In the center of the coal-mining area, measured uplift velocities reached a maximum of 18 mm/year during the ENVISAT period, while they subsided at −12 mm/year during the ERS-1/2 period. Mean velocities in the western and eastern parts of the coalfield area have decreased since the last MT-InSAR measurements were performed using Sentinel-1A, while the Zolder coal mine continues to rise at a faster-than-average rate of a maximum of 16 mm/year. The eastern part of the coalfield is still uplifting, while its rate has been reduced from 18 mm/year (ERS-1/2) to 9 mm/year (Sentinel-1A) since the beginning of the radar–satellite observations. Time-series data from the two GNSS stations present in the study area were used for a local comparison with the evolution of ground movements observed by MT-InSAR. Two leveling campaigns (2000, 2013) were also used to make comparisons with the MT-InSAR data. The station’s measurements and the leveling data were in line with the MT-InSAR data. Overall, major ground movements are obviously limited to an extension of the actual underground-mining works and rapidly diminish outside of them.

<p>A combination of historical levelling surveys, recent Global Navigation Satellite System (GNSS) campaign, and Persistent Scatterers Interferometry (PSI) measurements reveal that the harbour of Antwerp in Belgium has been sinking for the last 77 years. By integrating recently acquired data using PSI and historic databases, this study aims to provide the longest possible time series of data coverage for ground deformation in Antwerp. All data on subsidence in the area is assessed using multiple techniques and has been coherently included in a Geographic Information System (GIS). The long-term impact of ground subsidence on the harbour potentially has both natural and human-caused sources.</p> <p>The oldest dataset is a map of altitude changes in Belgium, based on a comparison of two first-order levelling surveys conducted in 1946-1948 and between 1976-1980 (Pissart and Lambot, 1989). The iso-displacement map for the entire country was calculated by subtracting the elevation map of the second levelling network from the first. The harbour of Antwerp was crossed by two iso-displacement lines of -20 and -10 mm, representing the overall displacement values over 31 years. This historical data demonstrates that there was a minor sinking in the region likely linked to natural consolidation when the anthropogenic changes in the harbour had not been made.</p> <p>As the second dataset, three PSI datasets including ERS1/2, Envisat, and Sentinel-1A spanning the area in the periods 1991-2005, 2003-2010, and 2016-2019 respectively were collected and post-processed. The rate of subsidence in the Antwerp harbor and its city centre differs noticeably from one another, based on this data set. The average velocity of PS data in the city centre is 0.002, -0.06, and -0.6 mm/year and in the harbour is -0.83, -2.71, and -1.62 mm/year during the three time spans (Declercq et al., 2021). This study extends Sentinel-1A processing until 2022.</p> <p>Among the 33 permanent Real-Time Kinematic (RTK) GNSS stations, there are three available stations to monitor the deformation of the region. ANTW (ANTWerp) and ATWR (AnTWeRp) are 70 meters away from each other and both are located within the city centre, and BEZA (BErendrecht-ZAndvliet-Lillo) is in the northeast of harbour. The vertical velocities at the locations of ANTW, ATWR, and BEZA during the periods 2003-2018, 2018-present, and 2010-present, are measured as -0.5, -1.9, and –2.2 mm/year respectively.</p> <p>First, occurring at a rate of a sub-millimetre per year between 1946 and 1980 as measured in the levelling survey, land subsidence has recently increased substantially, reaching a maximum rate of -7 mm/year observed by the PSI technique. The previous low rate of subsidence as measured by the levelling shows that the natural consolidation of Holocene sediments probably occurred from the beginning. However, this sinking has increased recently, as shown by the most recent PSI and GNSS data. This is probably mostly a man-induced process linked to the consolidation of the constructed backfill and its underlying layer due to its overpressure, together with the consolidation of the most compressible and less permeable layers (aquitards) due to pore pressure decrease induced by groundwater pumping in the aquifers.</p> <p> </p>

The Urban Geo Footprint (UGF) is a project currently developed in the framework of the EuroGeoSurvey Urban Geology Expert Group (UGEG) and specifically focused on the geo-environmental pressures in urban areas. The main goal of the study is to set up a classification tool (UGF) aimed to identify the main geological features that could influence and/or interfer with (ongoing) anthropic activities within urban catchments. The following main drivers are defined in the «UGF framework»: Geology, Climate, Geohazards, Geomorphology, Subsoil anthropic pressure. Each driving factor is articulated in quantitative and indexed (using scores) parameters. At the present early stage all these parameters are going to be indexed and weighted based on two levels of investigation: “basic” and “advanced”. The final result for each city is the “UGF INDEX” coming from the combination of all the drivers specific scores. The higher the index value, the higher the geotechnical and environmental complexity of the urbanized catchment. The expected outcomes of the UGF urban areas indexing are: * A classification of cities according to their geological setting and climatic features, eventually allowing their clustering and supporting sharing of knowledge and capabilities among urban areas. * Better understanding of geo-environment processes possibly interacting with urban subsurface and ground infrastructures, thus also encouraging and support cities’ subsurface resilience for sustainable (future) growth. * Help for better assessing the ‘economic’ and ‘social well-being’ benefits (i.e. in terms of ‘geological resilience’) that could derive from urban planning associated to subsoil knowledge. * A fact-sheet referred to the subsoil of each city, to be progressively updated. Other objectives of the project are: * Contributing to develop a method for the comparison of data from different environmental urban contexts. * Improving the European collaboration and, therefore, the exchange of ideas on good practices to increase urban areas’ resilience. * Improving citizens' awareness of both the resources and the threats associated with geology. * Produce a tool for decision makers support (e.g. urban planning, hazards prevention) in order to obtain economical and social well-being benefits.

Interferometric Synthetic Aperture Radar (InSAR) provides essential information dealing with different natural hazards caused by hydrogeological processes turned into subsidence (Lu et al., 2010). Among all geodetic techniques for monitoring land surface deformation, InSAR has demonstrated the most precise observations in both high spatial and temporal resolution (Dehghani et al., 2009). Different cities of Belgium are subject to land subsidence mostly induced by groundwater over-exploitation. In this study, we present Persistent Scatterer (PS-InSAR) over Belgium to highlight land surface deformation between 2003 to 2010. To this purpose, large-scale interferometry is accomplished by applying the PS-InSAR algorithm on three tracks of ENVISAT ASAR radar images covering the entire country. To provide an integrated land surface velocity map from several single acquisitions, eight stacks of ENVISAT ASAR C-band frames of Single Look Complex (SLC) data acquired from track 380, 423, and 466 spanning from 2003 to 2010 are used. Time series of deformation and mean velocity map are two products of applying PS-InSAR on the dataset. Joining single interferograms generated from successive frames along their acquisition tracks makes a randomly directed phase ramp in the mean velocity map due to atmospheric effects. The atmospheric effect composed of vertical and turbulent components is one of the most important error sources in using space-based deformation monitoring approaches. Monitoring land surface deformations, the atmospheric artifacts could mask real values of deformation phase calculated by different InSAR methodologies (Yu et al., 2018). To address this problem, different methods having different degrees of accuracy are widely suggested in the literature (Xiao et al., 2021). The patchy active deforming areas over Belgium along with a variety of atmospheric conditions through time and very slow ground deformation velocities make it a perfect case study for applying different proposed approaches for reducing the atmospheric effects. These approaches could be categorized into two main groups: i) those which are method-dependent and reduce all stochastic residual noise through processing, and ii) those which are based on external data such as meteorological features. The main advantage of the first group is that using them will not require any external data. However, the drawback is that the high spatial variability of the atmospheric artifact is disregarded by applying them. Overcoming this drawback, using professional GPS data is the most accurate method of the second group. Zenith Total Delay (ZTD) measurements are provided with the highest temporal resolution by GPS; therefore, additional uncertainties are inhibited (Yu et al., 2018). Using this method is an ongoing part of this study, but before that the Generic Atmospheric Correction Online Service for InSAR (GACOS) has been applied. The GACOS procedure is a developed package in the TRAIN software. Applying this procedure to the interferograms showed no tangible changes in them. In this study which is being carried out as part of the BRAIN BESLSPO project: "monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements (LASUGEO)", we benefit from ZTD files which are by-products of GNSS processing to mitigate atmospheric effects.

Sedimentary rocks can record signals produced by highly complex processes. These signals are generated by a progressive deposition of sediments which can be affected, mainly through the climate system, by regular astronomical cycles (i.e. Milankovitch cycles), and by irregular oscillations like the El Nin tilde o-Southern Oscillation. Also, usually through biological, chemical and/or physical post-depositional processes, the sedimentary records can be affected by pattern-creating heterogeneous processes. The noise in the signals further complicates the records, and the deposition rate (or sedimentation rate) can fluctuate, which greatly reduces the effectiveness of the classical stationary time-series analysis methods commonly used in cyclostratigraphy (i.e. the study of the cycles found in the sedimentary records).& nbsp; & nbsp; & nbsp; & nbsp;Faced with this multiplicity of processes, a common approach used in cyclostratigraphy is to reduce each signal to more manageable sub-signals, either over a given range of frequencies (e.g., by filtering), or by considering a continuum of constant frequencies (e.g., using transforms). This makes it possible to focus on the features of interest, commonly astronomical cycles. However, working with sub-signals is not trivial. Firstly, sub signals have a certain amount of cross-cancellation when they are summed back to reconstruct the initial signal. This means that in filters and in transforms, wiggles that are not present in the initial signal can appear in the sub-signals. Secondly, the sub-signals considered often cannot be summed to reconstruct the initial signal: this means that there are processes affecting the signal which remain unstudied.& nbsp; & nbsp; & nbsp; & nbsp; & nbsp;It is possible to take cross-cancellation into account and to consider the entire content of a signal by dividing the signal into a decomposition: a set of sub-signals that can be added back together to reconstruct the original signal. We discuss here how to reframe commonly used time-series analysis techniques in the context of decomposition, how they are affected by cross-cancellation, and how adequate they are for comprehending the whole signals. We also show that decomposition can be carried out by non-stationary time-series methods, which can minimise cross-cancellation, and have now reached sufficient maturity to tackle sedimentary records signals. We present novel tools to adapt non-stationary decomposition for cyclostratigraphic purposes, based on the concepts of Empirical Mode Decomposition (EMD) and Instantaneous Frequency (IF), mainly: (1) a fast Ensemble Empirical Mode Decomposition (EEMD) algorithm, (2) quality metrics for decomposition, and (3) plots to visualise instantaneous frequency, amplitude and frequency ratio.& nbsp; & nbsp; & nbsp; We illustrate the use of these tools by applying them on a greyscale signal from the site 926 of the Ocean Drilling Program, at Ceara Rise (western equatorial Atlantic), especially to identify and characterise the expression of astronomical cycles. The main goal is to show that by minimising cross-cancellation, we can apply in real signals what we call the wiggle-in-signal approach: making the sub-signals in the decomposition more representative of the expression, wiggle by wiggle, of all the processes affecting the signal (e.g., astronomical cycles). We finally argue that decomposition could be used as a practical standard output for time-series analysis interpretation of cyclostratigraphic signals.

The empirical power law relation (PR) between resonance frequency (f0), obtained from H/V spectral ratio analysis of ambient noise, and sediment thickness (h), obtained from boreholes, is frequently used in microzonation studies to predict bedrock depth. In this study, we demonstrate (i) how to optimally construct a PR by including the error on the picked f0 in the regression, and (ii) how to evaluate a regression quality by identifying the under- or overestimation of the sediment thickness prediction. We apply this methodology on f0 data derived from 74 ambient noise recordings acquired above boreholes that reach the Brabant Massif bedrock below Brussels (Belgium). Separating the f0 data into different subset based on the cover geology does not significantly improve the bedrock depth prediction because the cover geology in Brussels has common base layers. In Brussels, the PR relation h = 88.631.f0−1.683 is the best candidate to convert f0 to depth, with a prediction error of 10%. The Brussels PR was subsequently applied on a local survey (404 measurements; 25 km2) in southern Brussels with the aim to study Brussels’ Brabant Massif bedrock paleorelief. By linking the obtained paleorelief, Bouguer gravity data and aeromagnetic data, a NNW-SSE oriented, 20 m-high subsurface ridge could be identified. This ridge stands out because of differential erosion between less-resistant and hard quartzitic rock formations of the Brabant Massif. This subsurface ridge deflects the local radiation of seismic energy resulting in an anomaly in the otherwise regional consistent azimuthal dependency of the resonance frequency. We conclude that adding a polarisation analysis to a microzonation survey analysis allows detecting anomalous features in the paleorelief.

PSInSAR analyses across Belgium using ERS 1–2, ENVISAT, TerraSAR-X and Sentinel 1 allowed to follow several ground movements areas during the last three decades. Several areas of regional importance are affected by land subsidence processes that have been observed during this period (i.e. the alluvial plain of the Schelde estuary in Antwerpen, a large area in the West Flanders province and one around Merchtem area). Other land subsidence areas associated to old coal mining both in Flanders (Campine basin) and Wallonia (Hainaut and Liège province) are affected by progressive uplifting conditions linked to the mining aquifer piezometric rebound. It is extremely important to follow the spatio-temporal behavior of these phenomena to forecast their influences and their effects on the urban developments.

The StratigrapheR package proposes new concepts for the generation of lithological logs, or lithologs, in R. The generation of lithologs in a scripting environment opens new opportunities for the processing and analysis of stratified geological data. Among the new concepts presented: new plotting and data processing methodologies, new general R functions, and computer-oriented data conventions are provided. The package structure allows for these new concepts to be further improved, which can be done independently by any R user. The current limitations of the package are highlighted, along with the limitations in R for geological data processing, to help identify the best paths for improvements. Introduction StratigrapheR is a package implemented in the open-source programming environment R. StratigrapheR endeavors to explore new concepts to process stratified geological data. These concepts are provided to answer a major difficulty posed by such data; namely a large amount of field observations of varied nature, sometimes localized and small-scale, can carry information on large-scale processes. Visualizing the relevant observations all at once is therefore difficult. The usual answer to this problem in successions of stratified rocks is to report observations in a schematic form: the lithological log, or litholog (e.g., Fig. 1). The litholog is an essential tool in sedimentology and stratigraphy and proves to be equally invaluable in other fields such as volcanology, igneous petrology, or paleontology. Ideally, any data contained in a litholog should be available in a reproducible form. Therefore, the challenge at hand is what we would call "from art to useful data"; how can we best extract and/or process the information contained in a litholog, designed to be as visually informative as possible (see again Fig. 1). 28 29 30 31 32 33 34 44 45a 45b 45c 46 47 48 49 51 35 52a 52b 60a 60b 60c 61 HIATUS lamellar stromatoporoids branching stromatoporoids lamellar tabulate corals branching tabulate corals brachiopods crinoids receptaculitids small fenestrae large fenestrae

The coupled effects of climate change, sea-level rise, and land sinking in estuaries/alluvial plains prone to inundation and flooding mean that reliable estimation of land movements/subsidence is becoming more crucial. During the last few decades, land subsidence has been monitored by precise and continuous geodetic measurements either from space or using terrestrial techniques. Among them, the Persistent Scaterrer Interferometry (PSInSAR) technique is used on the entire Belgian territory to detect, map and interpret the identified ground movements observed since 1992. Here the research focuses on one of the biggest cities in Belgium that became the second European harbour with giant docks and the deepening of the Scheldt river allowing the navigation of the largest container vessels. The areas along the embankments of the Scheldt river and the harbour facilities are associated to Holocene fluviatile deposits overlain by recent landfills. These sedimentary deposits and human-made landfills are affected by important and ongoing land subsidence phenomena. The land subsidence process is highlighted by an annual average Line of Sight (LOS) velocity of about −3.4 mm/year during the years 1992–2001 (ERS1/2 datasets), followed by an annual average LOS velocity of about −2.71 mm/year and −2.11 mm/year, respectively, during the years 2003–2010 (ENVISAT) and 2016–2019 (Sentinel 1A). The Synthetic Aperture Radar (SAR) imagery data indicate a progressive decrease in the average annual velocities on a global scale independently of important local variations in different districts along the Scheldt river. On the contrary, the city centre and the old historic centre of Antwerp are not affected by negative LOS velocities, indicating stable ground conditions. A geological interpretation of this difference in settlement behaviour between the different areas is provided.

A land subsidence affecting several towns at the joining limits of the Belgian Provinces of East Flanders, Antwerp and Flemish Brabant is followed during the last three decades. ERS 1–2, ENVISAT, TerraSAR-X and Sentinel-1A satellites SAR scenes were processed from 1992 till October 2020 to map the land subsidence evolution. The subsidence corresponds to a surface area of 220 km 2 during the ERS 1/2 time interval distributed over three distinct subsidence bowls. During the ENVISAT and TerraSAR-X time interval, only one residual subsidence bowl was mapped affecting a surface area of about 70 km 2 . Several towns (Londerzeel and Steenhuffel) remained in the center of the subsidence bowl. The annual average negative velocity values range between −5.99 and −0.5 mm/year. During the Sentinel-1A period, the subsidence bowl has lost half of its surface reaching 36 km 2 . The LOS velocity values have also decreased during the period 2016–2020.