Surface displacement due to groundwater exploitation in the Lorca (Murcia, Spain) region.

Lowering of the groundwater table is a significant problem in Mediterranean coastal areas, leading to saltwater intrusion, drying of wetlands, and the disappearance of rivers (Coccossis and Hénocque, 2001). Aquifer overdraft has been a concern for the management of the water resources, due to the potential irreversible loss of aquifer storage caused by aquifer-system compaction, and associated land subsidence (Galloway and Hoffmann, 2007). From a mechanical point of view, groundwater extraction from a confined aquifer reduces groundwater pore pressure. Because the overburden remains unchanged, the effective stress on the grain matrix of the aquifer increases, and the volume of the confined aquifer decreases, resulting in compaction and triggering surface subsidence. Therefore, the control of land subsidence could serve as a proxy for the management of the pore pressure change and groundwater flows in underlying aquifers (Galloway and Hoffmann, 2007). Ground subsidence induced by overexploitation of aquifers is a common problem affecting urban areas and can be well characterized by radar interferometry (Tomas et al., 2005; Herrera et al., 2009 and 2010, Bru et al., 2010). Our main interest is the study of the ground deformation occurring in the Lorca area, where ground deformation data indicate large-scale deformation being of the highest rates of groundwater-related land subsidence recorded in Europe (>10cm/yr) (González and Fernández, 2011; Boni et al., 2015). This deformation study will be complemented by the development, improvement and implementation of the necessary tools that will allow modelling and interpretation of the observations, as well as to evaluate possible interactions with other phenomena, such as the potential to influence faulting on nearby faults.

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