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Gerardo Herrera, Instituto Geológico y Minero de España (Spain)
Joaquin Mulas, Instituto Geológico y Minero de España (Spain)
Geraint Cooksley, Altamira Informtation (Spain)
Javier Duro, Altamira Informtation (Spain)
Alain Arnaud, Altamira Informtation (Spain)
Rogelio de la Vega-Panizo, ETS Ing. Minas-Univ. Politecnica Madrid (Spain)
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The combination of numerous SAR images performed by Stable Point Network (SPN) technique, allow the estimation of the deformation evolution with milimetric precision. Terrafirma is an ESA GMES project aimed at improving safety and reducing economic loss by using advanced differential interferometry (A-DInSAR) to measure terrain motion from satellite radar data. Within this framework SPN technique has been applied from 1995 to 2005 to study subsidence phenomena in the Vega Media of Segura River, Murcia (SE Spain). Accumulated sediments in this area constitute an aquifer that had been scarcely exploited in the past.
Nevertheless, the recent growing in population and changes in agricultural practices has favored the intense exploitation of this aquifer. During the 1992-1995 drought, excessive water pumping caused a decrease from 5 to 16 m in the water table causing a moderate subsidence in the metropolitan area of Murcia city. This phenomenon caused damages in more than 150 buildings and public structures that were evaluated over 50 million euros causing a high social alarm.
The geological materials that constitute the aquifer system of the Vega Media belong to a detritus packet that can reach a thickness of 250 m. A numerical modeling of ground consolidation has been performed using finite elements software program Zsoil v4 (2D), which allow the tense-deformational calculation with hydraulic coupling according to the water table evolution history. In 2001, a set 21 extensometers were installed in four areas of maximum theoretical settlement (south and southeast of the city). SPN ground deformation measurements have been compared with compressible layer thickness, piezometric level evolution, finite element model estimations of the deformation, and with available instrumental data. The results have lead to a greater understanding of the subsidence process and impacts, and, therefore, it has become a cost effective tool for land use planning and risk assessment.
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