Advanced interpretation of subsidence in Murcia (SE Spain) using A-DInSAR data – modelling and validation

Subsidence is a natural hazard that affects wide areas in the world causing important economic costs annually. This phenomenon has occurred in the metropolitan area of Murcia City (SE Spain) as a result of groundwater overexploitation. In this work aquifer system subsidence is investigated using an advanced differential SAR interferometry remote sensing technique (A-DInSAR) called Stable Point Network (SPN). The SPN derived displacement results, mainly the velocity displacement maps and the time series of the displacement, reveal that in the period 2004–2008 the rate of subsidence in Murcia metropolitan area doubled with respect to the previous period from 1995 to 2005. The acceleration of the deformation phenomenon is explained by the drought period started in 2006. The comparison of the temporal evolution of the displacements measured with the extensometers and the SPN technique shows an average absolute error of 3.9±3.8 mm. Finally, results from a finite element model developed to simulate the recorded time history subsidence from known water table height changes compares well with the SPN displacement time series estimations. This result demonstrates the potential of A-DInSAR techniques to validate subsidence prediction models as an alternative to using instrumental ground based techniques for validation.

Relationship between piezometric level and ground deformations measured by means of DInSAR in the Vega Media of the Segura River (Spain)

Differential SAR Interferometry (DInSAR) is a remote sensing method with the well demonstrated ability to monitor geological hazards like earthquakes, landslides and subsidence. Among all these hazards, subsidence involves the settlement of the ground surface affecting wide areas. Frequently, subsidence is induced by overexploitation of aquifers and constitutes a common problem that affects developed societies. The excessive pumping of underground water decreases the piezometric level in the subsoil and, as a consequence, increases the effective stresses with depth causing a consolidation of the soil column. This consolidation originates a settlement of ground surface that must be withstood by civil structures built on these areas. In this paper we make use of an advanced DInSAR approach - the Coherent Pixels Technique (CPT) [1] - to monitor subsidence induced by aquifer overexploitation in the Vega Media of the Segura River (SE Spain) from 1993 to the present. 28 ERS-1/2 scenes covering a time interval of about 10 years were used to study this phenomenon. The deformation map retrieved with CPT technique shows settlements of up to 80 mm at some points of the studied zone. These values agree with data obtained by means of borehole extensometers, but not with the distribution of damaged buildings, well points and basements, because the occurrence of damages also depends on the structural quality of the buildings and their foundations. The most interesting relationship observed is the one existing between piezometric changes, settlement evolution and local geology. Three main patterns of ground surface and piezometric level behaviour have been distinguished for the study zone during this period: 1) areas where deformation occurs while ground conditions remain altered (recent deformable sediments), 2) areas with no deformation (old and non-deformable materials), and 3) areas where ground deformation mimics piezometric level changes (expansive soils). The temporal relationship between deformation patterns and soil characteristics has been analysed in this work, showing a delay between them. Moreover, this technique has allowed the measurement of ground subsidence for a period (1993-1995) where no instrument information was available.

Monitorización de la subsidencia del terreno en la Vega Media del río Segura mediante Interferometría SAR diferencial (DInSAR)

Ground subsidence caused by aquifer exploitation is a geotechnical hazard that affects wide areas, causing important economic damages. This phenomenon is due to soil consolidation produced by the increase of effective stress caused by piezometric depletion. In this work a Remote Sensing Technique called Coherent Pixel (CPT) is applied to monitor subsidence in the Vega Media of the Segura River during a period of eleven years.

Subsidence activity maps derived from DInSAR data: Orihuela case study

A new methodology is proposed to produce subsidence activity maps based on the geostatistical analysis of persistent scatterer interferometry (PSI) data. PSI displacement measurements are interpolated based on conditional Sequential Gaussian Simulation (SGS) to calculate multiple equiprobable realizations of subsidence. The result from this process is a series of interpolated subsidence values, with an estimation of the spatial variability and a confidence level on the interpolation. These maps complement the PSI displacement map, improving the identification of wide subsiding areas at a regional scale. At a local scale, they can be used to identify buildings susceptible to suffer subsidence related damages. In order to do so, it is necessary to calculate the maximum differential settlement and the maximum angular distortion for each building of the study area. Based on PSI-derived parameters those buildings in which the serviceability limit state has been exceeded, and where in situ forensic analysis should be made, can be automatically identified. This methodology has been tested in the city of Orihuela (SE Spain) for the study of historical buildings damaged during the last two decades by subsidence due to aquifer overexploitation. The qualitative evaluation of the results from the methodology carried out in buildings where damages have been reported shows a success rate of 100%.

Twenty-year advanced DInSAR analysis of severe land subsidence: The Alto Guadalentín Basin (Spain) case study

A twenty-year period of severe land subsidence evolution in the Alto Guadalentín Basin (southeast Spain) is monitored using multi-sensor SAR images, processed by advanced differential interferometric synthetic aperture radar (DInSAR) techniques. The SAR images used in this study consist of four datasets acquired by ERS-1/2, ENVISAT, ALOS and COSMO-SkyMed satellites between 1992 and 2012. The integration of ground surface displacement maps retrieved for different time periods allows us to quantify up to 2.50 m of cumulated displacements that occurred between 1992 and 2012 in the Alto Guadalentín Basin. DInSAR results were locally compared with global positioning system (GPS) data available for two continuous stations located in the study area, demonstrating the high consistency of local vertical motion measurements between the two different surveying techniques. An average absolute error of 4.6 ± 4 mm for the ALOS data and of 4.8 ± 3.5 mm for the COSMO-SkyMed data confirmed the reliability of the analysis. The spatial analysis of DInSAR ground surface displacement reveals a direct correlation with the thickness of the compressible alluvial deposits. Detected ground subsidence in the past 20 years is most likely a consequence of a 100–200 m groundwater level drop that has persisted since the 1970s due to the overexploitation of the Alto Guadalentín aquifer system. The negative gradient of the pore pressure is responsible for the extremely slow consolidation of a very thick (> 100 m) layer of fine-grained silt and clay layers with low vertical hydraulic permeability (approximately 50 mm/h) wherein the maximum settlement has still not been reached.

Regional subsidence modelling in Murcia city (SE Spain) using 1-D vertical finite element analysis and 2-D interpolation of ground surface displacements

Subsidence is a hazard that may have natural or anthropogenic origin causing important economic losses. The area of Murcia city (SE Spain) has been affected by subsidence due to groundwater overexploitation since the year 1992. The main observed historical piezometric level declines occurred in the periods 1982–1984, 1992–1995 and 2004–2008 and showed a close correlation with the temporal evolution of ground displacements. Since 2008, the pressure recovery in the aquifer has led to an uplift of the ground surface that has been detected by the extensometers. In the present work an elastic hydro-mechanical finite element code has been used to compute the subsidence time series for 24 geotechnical boreholes, prescribing the measured groundwater table evolution. The achieved results have been compared with the displacements estimated through an advanced DInSAR technique and measured by the extensometers. These spatio-temporal comparisons have showed that, in spite of the limited geomechanical data available, the model has turned out to satisfactorily reproduce the subsidence phenomenon affecting Murcia City. The model will allow the prediction of future induced deformations and the consequences of any piezometric level variation in the study area.

Subsidence damage assessment of a Gothic church using differential interferometry and field data

The Santas Justa and Rufina Gothic church (fourteenth century) has suffered several physical, mechanical, chemical, and biochemical types of pathologies along its history: rock alveolization, efflorescence, biological activity, and capillary ascent of groundwater. However, during the last two decades, a new phenomenon has seriously affected the church: ground subsidence caused by aquifer overexploitation. Subsidence is a process that affects the whole Vega Baja of the Segura River basin and consists of gradual sinking in the ground surface caused by soil consolidation due to a pore pressure decrease. This phenomenon has been studied by differential synthetic aperture radar interferometry techniques, which illustrate settlements up to 100 mm for the 1993–2009 period for the whole Orihuela city. Although no differential synthetic aperture radar interferometry information is available for the church due to the loss of interferometric coherence, the spatial analysis of nearby deformation combined with fieldwork has advanced the current understanding on the mechanisms that affect the Santas Justa and Rufina church. These results show the potential interest and the limitations of using this remote sensing technique as a complementary tool for the forensic analysis of building structures.

Imaging Land Subsidence Induced by Groundwater Extraction in Beijing (China) Using Satellite Radar Interferometry

Beijing is one of the most water-stressed cities in the world. Due to over-exploitation of groundwater, the Beijing region has been suffering from land subsidence since 1935. In this study, the Small Baseline InSAR technique has been employed to process Envisat ASAR images acquired between 2003 and 2010 and TerraSAR-X stripmap images collected from 2010 to 2011 to investigate land subsidence in the Beijing region. The maximum subsidence is seen in the eastern part of Beijing with a rate greater than 100 mm/year. Comparisons between InSAR and GPS derived subsidence rates show an RMS difference of 2.94 mm/year with a mean of 2.41 ± 1.84 mm/year. In addition, a high correlation was observed between InSAR subsidence rate maps derived from two different datasets (i.e., Envisat and TerraSAR-X). These demonstrate once again that InSAR is a powerful tool for monitoring land subsidence. InSAR derived subsidence rate maps have allowed for a comprehensive spatio-temporal analysis to identify the main triggering factors of land subsidence. Some interesting relationships in terms of land subsidence were found with groundwater level, active faults, accumulated soft soil thickness and different aquifer types. Furthermore, a relationship with the distances to pumping wells was also recognized in this work.

Uso do zoneamento ambiental do Médio Rio Grande na sub-bacia hidrográfica do Ribeirão Bocaina - Passos/MG

Este trabalho é parte integrante do Projeto Grande Minas - União pelas Águas, que realizou o Zoneamento Ambiental das Sub-bacias Hidrográficas dos Afluentes Mineiros do Médio Rio Grande. Após a obtenção dos produtos finais do zoneamento, entra-se agora, na fase de “Implementação”, ou seja, de sua aplicação direta para contribuir no processo de gestão dos recursos hídricos das sub-bacias hidrográficas da área de estudo. Neste trabalho estuda-se, especificamente, a sub-bacia hidrográfica do Ribeirão Bocaina, considerada uma das 34 sub-bacias que envolvem a Bacia Hidrográfica dos Afluentes Mineiros do Médio Rio Grande e situa-se no município de Passos-MG, possuindo uma área de 457,9 km². O trabalho busca dar uma contribuição para a gestão dos recursos hídricos nesta sub-bacia, que vem sofrendo com a degradação do seu recurso hídrico. O objetivo é disponibilizar instrumentos cartográficos para subsidiar a gestão dos recursos hídricos e, com isto, contribuir com a sua preservação e uso sustentável. A sistemática metodológica envolve uma análise dos aspectos legais da área de estudo; a construção de um Banco de Dados Digital georreferenciado com informações sobre os meios físico, biótico e socioeconômico da sub-bacia e a produção de uma carta derivada, de cunho interpretativo e de fácil leitura, que possa ser utilizada diretamente pelo gestor público nas tomadas de decisões. A base digital produzida conta com uma série de mapas digitais, dentre eles: mapas climáticos, de solos, declividades, geomorfológico, geológico, de sistemas aquíferos, hidrográfico, uso e ocupação do solo. Com relação à carta derivada, destaca os terrenos que apresentam maior predisposição à alterações diretas nos recursos hídricos.

Acompanhamento da construção de uma captação de água subterrânea

Tese de mestrado, Geologia Aplicada (Hidrogeologia) Universidade de Lisboa, Faculdade de Ciências, 2016

Whole rock analytical techniques and glas analytical techniques of silicic magmas from the South East Rift, Manus Basin

There has been much recent interest in the origin of silicic magmas at spreading centres away from any possible influence of continental crust. Here we present major and trace element data for 29 glasses (and 55 whole-rocks) sampled from a 40 km segment of the South East Rift in the Manus Basin that span the full compositional continuum from basalt to rhyolite (50-75 wt % SiO2). The glass data are accompanied by Sr-Nd-Pb, O and U-Th-Ra isotope data for selected samples. These overlap the ranges for published data from this part of the Manus Basin. Limited increases in Cl/K ratios with increasing SiO2, La-SiO2 and Yb-SiO2 relationships, and the oxygen isotope data rule out models in which the more silicic lavas result from partial melting of altered oceanic crust or altered oceanic gabbros. Rather, the data form a coherent array that is suggestive of closed-system fractional crystallization and this is well simulated by MELTS models run at 0.2 GPa and QFM (quartz-fayalite-magnetite buffer) with 1 wt % H2O, using a parental magma chosen from the basaltic glasses. Although some assimilation of altered oceanic crust or gabbro cannot be completely ruled out, there is no evidence that this plays an important role in the origin of the silicic lavas. The U-series disequilibria are dominated by 238U and 226Ra excesses that limit the timescale of differentiation to less than a few millennia. Overall, the data point to rapid evolution in relatively small magma lenses located near the base of thick oceanic crust; we speculate that this was coupled with relatively low rates of basaltic recharge. A similar model may be applicable to the generation of silicic magmas elsewhere in the ocean basins.

Geochemistry and stable isotope record of the hydtrothermally altered lower sheeted dike complex in ODP Hole 140-504B

Drilling during Legs 137 and 140 of the Ocean Drilling Program deepened Hole 504B, the only hole to penetrate through the volcanic section and into the underlying hydrothermally altered sheeted dike complex, by 438.1 m to a total depth of 2000.4 meters below seafloor. This paper presents the secondary mineralogy, bulk-rock sulfur contents, and stable isotopic (O, S) compositions, plus oxygen isotopic compositions of secondary minerals from the lower sheeted dike complex drilled during Legs 137 and 140. Various evidence indicates higher temperatures of hydrothermal alteration in the lower dikes than in the upper dikes, including: the local presence of secondary clinopyroxene in the lower dikes; secondary anorthite and hornblende in the lower dikes vs. mainly actinolite and albite-oligoclase in the upper dikes; generally increasing Al and Ti contents of amphibole downward in the dike section; and greater 18O depletions of the lower dikes (d18O = 3.6-5.0 per mil) compared with the upper dikes. Early high-temperature alteration stages (T = 350°-500°C) resulted in 18O depletions and losses of metals (Cu, Zn) and sulfur from the rocks. Local incorporation of reduced seawater sulfate led to elevated d34S values of sulfide in the rocks (up to 2.5 per mil). Quartz + epidote formed in crosscutting veins at temperatures of 310°-320°C from more evolved fluids (d18O = 1 per mil). Late-stage lower-temperature (~250°C) reactions producing albite, prehnite, and zeolites in the rocks caused slight 18O enrichments, but these were insufficient to offset the 18O depletions caused by earlier higher-temperature reactions. Addition of anhydrite to the rocks during seawater recharge led to increased S contents of rocks that had previously lost S during axial hydrothermal alteration, and to further increases in d34S values of total S in the rocks (up to 12 per mil). Despite the evidence for seawater recharge to near the base of the sheeted dike complex, the paucity of late zeolites in the lower dikes suggests that late-stage, off-axis circulation was mainly restricted to the volcanics and shallowest dikes, or to localized high-permeability zones (faults) at depth.

(Table 1) Lithium contents and isotopic composition in sediments from DSDP Holes 64-477 and 64-477A

Lithium isotopic compositions of hydrothermally altered sediments of Deep Sea Drilling Project (DSDP) site 477/477A, as well as high temperature vent fluids of the Guaymas Basin, have been determined to gain an understanding of lithium exchange during fluid-sediment interaction at this sediment-covered spreading center. Unaltered turbidite of the basin has a d6Li value of -10%, 5-7% heavier than fresh oceanic basalts. Contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value (-8%). Below the sill, sediments altered by a deep-seated hydrothermal system show strong depletions in lithium, while lithium isotopic compositions vary greatly, ranging from -11 to +1%. The shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals. The complexity of the isotope profile is attributed to inhomogeneity in mineral composition, the tortuous pathway of fluids and the temperature effect on isotopic fractionation. The range of lithium concentration and d6Li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment-free mid-ocean ridge systems. The lack of a distinct expression of sediment input is explained in terms of a flow-through system with continuous water recharge. The observations on the natural system agree well with the results of laboratory hydrothermal experiments. The experimental study demonstrates the importance of temperature, pressure, water/rock ratio, substrate composition and reaction time on the lithium isotopic composition of the reacted fluid. High temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as Guaymas are a source of lithium to the ocean. The ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones.

(Table 1) Gravity and pressure within the Sleipner area relative to ones at the reference station in 2002 and 2005

At Sleipner, CO2 is being separated from natural gas and injected into an underground saline aquifer for environmental purposes. Uncertainty in the aquifer temperature leads to uncertainty in the in situ density of CO2. In this study, gravity measurements were made over the injection site in 2002 and 2005 on top of 30 concrete benchmarks on the seafloor in order to constrain the in situ CO2 density. The gravity measurements have a repeatability of 4.3 µGal for 2003 and 3.5 µGal for 2005. The resulting time-lapse uncertainty is 5.3 µGal. Unexpected benchmark motions due to local sediment scouring contribute to the uncertainty. Forward gravity models are calculated based on both 3D seismic data and reservoir simulation models. The time-lapse gravity observations best fit a high temperature forward model based on the time-lapse 3D seismics, suggesting that the average in situ CO2 density is about to 530kg/m**3. Uncertainty in determining the average density is estimated to be ±65 kg/m**3 (95% confidence), however, this does not include uncertainties in the modeling. Additional seismic surveys and future gravity measurements will put better constraints on the CO2 density and continue to map out the CO2 flow.

Geohydrologic setting of and seepage from a water-supply canal, Indianapolis, Marion County, Indiana /

"November 1979."