Modeling the two- and three-dimensional displacement field in Lorca, Spain, subsidence and the global implications

Land subsidence associated with overexploitation of aquifers is a hazard that commonly affects large areas worldwide. The Lorca area, located in southeast Spain, has undergone one of the highest subsidence rates in Europe as a direct consequence of long-term aquifer exploitation. Previous studies carried out on the region assumed that the ground deformation retrieved from satellite radar interferometry corresponds only to vertical displacement. Here we report, for the first time, the two- and three-dimensional displacement field over the study area using synthetic aperture radar (SAR) data from Sentinel-1A images and Global Navigation Satellite System (GNSS) observations. By modeling this displacement, we provide new insights on the spatial and temporal evolution of the subsidence processes and on the main governing mechanisms. Additionally, we also demonstrate the importance of knowing both the vertical and horizontal components of the displacement to properly characterize similar hazards. Based on these results, we propose some general guidelines for the sustainable management and monitoring of land subsidence related to anthropogenic activities.Peer ReviewedPostprint (published version

Tracking hidden crisis in India's capital from space: implications of unsustainable groundwater use.

Funder: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZNational Capital Region (NCR, Delhi) in India is one of the fastest-growing metropolitan cities which is facing a severe water crisis due to increasing water demand. The over-extraction of groundwater, particularly from its unconsolidated alluvial deposits makes the region prone to subsidence. In this study, we investigated the effects of plummeting groundwater levels on land surface elevations in Delhi NCR using Sentinel-1 datasets acquired during the years 2014-2020. Our analysis reveals two distinct subsidence features in the study area with rates exceeding 11 cm/year in Kapashera-an urban village near IGI airport Delhi, and 3 cm/year in Faridabad throughout the study period. The subsidence in these two areas are accelerating and follows the depleting groundwater trend. The third region, Dwarka shows a shift from subsidence to uplift during the years which can be attributed to the strict government policies to regulate groundwater use and incentivizing rainwater harvesting. Further analysis using a classified risk map based on hazard risk and vulnerability approach highlights an approximate area of 100 square kilometers to be subjected to the highest risk level of ground movement, demanding urgent attention. The findings of this study are highly relevant for government agencies to formulate new policies against the over-exploitation of groundwater and to facilitate a sustainable and resilient groundwater management system in Delhi NCR

Modeling the two- and three-dimensional displacement field in Lorca, Spain, subsidence and the global implications

Land subsidence associated with overexploitation of aquifers is a hazard that commonly affects large areas worldwide. The Lorca area, located in southeast Spain, has undergone one of the highest subsidence rates in Europe as a direct consequence of long-term aquifer exploitation. Previous studies carried out on the region assumed that the ground deformation retrieved from satellite radar interferometry corresponds only to vertical displacement. Here we report, for the first time, the two- and three-dimensional displacement field over the study area using synthetic aperture radar (SAR) data from Sentinel-1A images and Global Navigation Satellite System (GNSS) observations. By modeling this displacement, we provide new insights on the spatial and temporal evolution of the subsidence processes and on the main governing mechanisms. Additionally, we also demonstrate the importance of knowing both the vertical and horizontal components of the displacement to properly characterize similar hazards. Based on these results, we propose some general guidelines for the sustainable management and monitoring of land subsidence related to anthropogenic activitie

New GPS Time Series Analysis and a Simplified Model to Compute an Accurate Seasonal Amplitude of Tropospheric Delay

Horizontal and vertical deformation of the Earth’s crust is due to a variety of different geophysical processes that take place on various spatiotemporal scales. The quality of the observations from spaced-based geodesy instruments such as Global Positioning System (GPS) and differential interferometric synthetic aperture radar (DInSAR) data for monitoring these deformations are dependent on numerous error sources. Therefore, accurately identifying and eliminating the dominant sources of the error, such as troposphere error in GPS signals, is fundamental to obtain high quality, sub-centimeter accuracy levels in positioning results. In this work, I present the results of double-differenced processing of five years of GPS data, between 2008 and 2012, for sparsely distributed GPS stations in southeastern Ontario and western Québec. I employ Bernese GPS Software Version 5.0 (BSW5.0) and found two optimal sub-networks which can provide high accuracy estimation of the position changes. I demonstrate good agreement between the resulted coordinate time series and the estimates of the crustal motions obtained from a global solution. In addition, I analyzed the GPS position time series by using a complex noise model, a combination of white and power-law noises. The estimated spectral index of the noise model demonstrates that the flicker noise is the dominant noise in most GPS stations in our study area. The interpretation of the observed velocities suggests that they provide an accurate constraint on glacial isostatic adjustment (GIA) prediction models. Based on a deeper analysis of these same GPS stations, I propose a model that accurately estimates the seasonal amplitude of zenith tropospheric delay (ZTD) error in the GPS data on local and regional spatial scales. I process the data for the period 2008 through 2012 from eight GPS stations in eastern Ontario and western Québec using precise point positioning (PPP) online analysis available from Natural Resource Canada (NRCan) (https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php). The model is an elevation-dependent model and is a function of the decay parameter of refractivity with altitude and the seasonal amplitude of refractivity computed from atmospheric data (pressure, temperature, and water vapor pressure) at a given reference station. I demonstrate that it can accurately estimate the seasonal amplitude of ZTD signals for the GPS stations at any altitude relative to that reference station. Based on the comparison of the observed seasonal amplitudes of the differenced ZTD at each station and the estimates from the proposed model, it can provide an accurate estimation for the stations under normal atmospheric conditions. The differenced ZTD is defined as the differences of ZTD derived from PPP at each station and ZTD at the reference station. Moreover, I successfully compute a five-year precipitable water vapor (PWV) at each GPS site, based on the ZTD derived from meteorological data and GPS processing. The results provide an accurate platform to monitor long-term climate changes and inform future weather predictions. In an extension of this research, I analyze DInSAR data between 2014 and 2017 with high temporal and spatial resolution, from Kilauea volcano in Hawaii in order to derive the spatial and temporal pattern of the seasonal amplitude of ZTD. I propose an elevation-dependent model by the data from a radiosonde station and observations at a surface weather station for modeling the seasonal amplitudes of ZTD at any arbitrary elevation. The results obtained from this model fit the vertical profile of the observed seasonal amplitude of ZTD in DInSAR data, increasing systematically from the elevation of the DInSAR reference point. I demonstrate that the proposed model could be used to estimate the seasonal amplitude of the differenced ZTD at each GPS station within a local network with high accuracy. The results of this study concluded that, employing this model in GPS processing applications eliminates the need for the meteorological observations at each GPS site

Assessment of landslide susceptibility in Structurally Complex Formations by integration of different A-DInSAR techniques

Instability events are recurring phenomena in Southern Italy due to its geological history and tectonic-geomorphological evolution leading to the occurrence of several formations identified as Structurally Complex Formations (SCFs; Esu, 1977) in a territory mainly composed of densely populated areas also in mountainous and hilly regions. SCFs are clay-dominant terrains that, usually, give origin from very-slow to extremely-slow phenomena (Cruden and Varnes, 1996) with a long evolutionary history made up of multiple reactivations that makes difficult their identification, monitoring and susceptibility evaluation. The study has been carried out from point-wise (Bisaccia, Costa della Gaveta and Nerano cases) to wide areas (Palermo province case) where crops out SCFs as the Termini sandstones Formation (CARG, 2011), the Varicoloured Clays of Calaggio Formation (Ciaranfi et al., 1973), the Varicoloured Clays Unit (Mattioni et al., 2006) the Sicilide Unit (Vitale and Ciarcia, 2013 and references therein), the Numidian Flysch (Johansson et al., 1998) and the Corleone Calcarenites (Catalano R. et al., 2002). The aim of this thesis is to produce updated Landslide Inventory Maps and, whenever possible, Landslide Susceptibility Maps following a new approach during the landslide mapping and landslide monitoring stages. The Landslide Inventory Maps have taken into account the combination of geological, geomorphological, and stereoscopic surveys, as well as engineering geological investigations, namely conventional techniques. In addition innovative Advanced-Differential Interferometry Synthetic Aperture Radar (A-DInSAR) techniques have been used: the Coherent Pixels Technique – CPT (Mora et al., 2003; Blanco et al., 2008), the Intermittent Small BAseline Subset – ISBAS (Sowter et al., 2013) and the Ground-Based Synthetic Aperture Radar. Finally, the Weight of Evidence method (van Westen, 1993) has been chosen to generate the Landslide Susceptibility Maps only for the point-wise studies. In the case of Nerano (Province of Naples), the ISBAS analysis on ENVISAT images (for the period 2003-2010) has been carried out and compared with inclinometric and rainfall data. These have revealed several reactivations of a rotational slide + earth flow (Cruden and Varnes, 1996) that involves reworked clay olistostromes and limestone olistoliths inside the Termini sandstones Formation; even in recent years the landslide, despite many engineering works, has given evidence of a continuing activity. The results highlight a very slow movement in the detachment zone (<1 mm/yr), which assumes slightly higher values in the accumulation area (5 mm/yr). The Landslide Susceptibility Map confirms the high levels in the flow track and the accumulation area. In Bisaccia (Province of Avellino), a conglomeratic slab undergoes a Deep Seated Gravitational Slope Deformation (DSGSD; Pasuto and Soldati, 2013 and references therein) due to the bedrock consolidation, made of the Varicoloured Clays of Calaggio Formation. Here the CPT processing on ENVISAT images (covering the period between 2002 and 2010), displays a vertical displacement for the town center, suffering a progressively increasing velocity from the southern (4.2 mm/yr) to the northern (15.5 mm/yr) portion of the slab that localizes four different sectors. The pattern is confirmed from the building damage map. The landslides susceptibility reaches the highest values in the adjacent valleys and at the edges of each sector. Multiple datasets have been employed for the Costa della Gaveta case-study (Province of Potenza), these encompass: ENVISAT, TerraSAR-X and COSMO-SkyMed constellations together with Ground Based Synthetic Aperture Radar (GBSAR). The A-DInSAR data have been compared with stereoscopic analysis and the available rainfall and inclinometric data. The analysis allows for the identification of 16 landslides (complexes and earth flows; Cruden and Varnes, 1996) developed in the Varicoloured Clays Unit that show, according to all the existing instruments, velocities between 1.5 and 30 mm/yr. The western side of Costa della Gaveta slope is the portion which suffers the highest landslides susceptibility levels. In the Province of Palermo (northwestern Sicily) information deriving from A-DInSAR processing, specifically the ISBAS technique, have been focused on three subareas (Piana degli Albanesi, Marineo and Ventimiglia di Sicilia) for a total extension of 182 Km2 where standard A-DInSAR algorithms showed limitations due to the widespread presence of densely vegetated areas. The radar-detected landslides have been validated through field geomorphological mapping and stereoscopic analysis proving to be highly consistent especially with slow phenomena. The outcome has allowed to confirm 152 preexisting landslides, to detect 81 new events and to change 133 previously mapped landslides, modifying their typology, boundary and/or state of activity. The study demonstrates how a better knowledge of landslide development and their cause-effect mechanisms provided by new Earth Observation techniques is useful for Landslide Inventory and Susceptibility Maps. The research project has been carried out at the University of Naples "Federico II", including nine months (September 2013 – May 2014) spent in the United Kingdom, at the British Geological Survey under the supervision of Dr. Francesca Cigna and Dr. Jordan Colm and at the University of Nottingham (Department of Civil Engineering), under the supervision of Dr. Andrew Sowter where the ISBAS technique has been recently developed

Response of saline reservoir to different phaseCO₂-brine: experimental tests and image-based modelling

Geological CO₂ storage in saline rocks is a promising method for meeting the target of net zero emission and minimizing the anthropogenic CO₂ emitted into the earth’s atmosphere. Storage of CO₂ in saline rocks triggers CO₂-brine-rock interaction that alters the properties of the rock. Properties of rocks are very crucial for the integrity and efficiency of the storage process. Changes in properties of the reservoir rocks due to CO₂-brine-rock interaction must be well predicted, as some changes can reduce the storage integrity of the reservoir. Considering the thermodynamics, phase behavior, solubility of CO₂ in brine, and the variable pressure-temperature conditions of the reservoir, there will be undissolved CO₂ in a CO₂ storage reservoir alongside the brine for a long time, and there is a potential for phase evolution of the undissolved CO₂. The phase of CO₂ influence the CO₂-brine-rock interaction, different phaseCO₂-brine have a unique effect on the properties of the reservoir rocks, Therefore, this study evaluates the effect of four different phaseCO₂-brine reservoir states on the properties of reservoir rocks using experimental and image-based approach. Samples were saturated with the different phaseCO₂-brine, then subjected to reservoir conditions in a triaxial compression test. The representative element volume (REV)/representative element area (REA) for the rock samples was determined from processed digital images, and rock properties were evaluated using digital rock physics and rock image analysis techniques. This research has evaluated the effect of different phaseCO₂-brine on deformation rate and deformation behavior, bulk modulus, compressibility, strength, and stiffness as well as porosity and permeability of sample reservoir rocks. Changes in pore geometry properties, porosity, and permeability of the rocks in CO₂ storage conditions with different phaseCO₂-brine have been evaluated using digital rock physics techniques. Microscopic rock image analysis has been applied to provide evidence of changes in micro-fabric, the topology of minerals, and elemental composition of minerals in saline rocks resulting from different phaseCO₂-br that can exist in a saline CO₂ storage reservoir. It was seen that the properties of the reservoir that are most affected by the scCO₂-br state of the reservoir include secondary fatigue rate, bulk modulus, shear strength, change in the topology of minerals after saturation as well as change in shape and flatness of pore surfaces. The properties of the reservoir that is most affected by the gCO₂-br state of the reservoir include primary fatigue rate, change in permeability due to stress, change in porosity due to stress, and change topology of minerals due to stress. For all samples, the roundness and smoothness of grains as well as smoothness of pores increased after compression while the roundness of pores decreased. Change in elemental composition in rock minerals in CO₂-brine-rock interaction was seen to depend on the reactivity of the mineral with CO₂ and/or brine and the presence of brine accelerates such change. Carbon, oxygen, and silicon can be used as index minerals for elemental changes in a CO₂-brine-rock system. The result of this work can be applied to predicting the effect the different possible phases of CO₂ will have on the deformation, geomechanics indices, and storage integrity of giant CO₂ storage fields such as Sleipner, In Salah, etc