Subsidence phenomena can occur naturally or by man-induced activities.
Due to the high porosity clay materials and peats are subjected to compaction that could result in differential settlements.
Limestones, dolomite, and gypsum may suffer a selective dissolution that originates typically along discontinuities. Natural cavities grow with time and the involved material may be weakened by weathering, and creep, with consequent risk of collapse.
Subsidence process related to hydrocompaction can typically interest loess, alluvial silts deposited by flood events in semi-arid basins, some tropical soils, and some artificial fills.
Also crustal sag can cause very low subsidence rate.
Man-made subsidence processes are related to civil engineers projects as tunneling or underground excavations, mining operations and environmental remediation works that include pumping, and oil & gas reservoir exploitation.
Wide subsiding areas developed where pumping activities interest sand aquifers interbedded with clay aquitards. Pumping from sand causes small, instantaneous, elastic, recoverable compaction of the sand. Compaction of clay is larger and inelastic, and it is non recoverable.
Houses or more in general infrastructures can be affected by slight to severe damages if located in correspondence of a subsiding area because of the development of low to high differential displacement rates.
InSAR-based displacement data provided by Fragile Srl can be very useful to perimeter and quantify the evolution in time and space of subsiding areas. It is also possible measure the induced deformations affecting houses and infrastructures involved in this deformation phenomenon.
InSAR results supplied by Fragile Srl can be successfully used for instance to understand which rate of deformation is caused by extraction activities and if plastic or elastic deformation occurred in the past.
InSAR analyses allow also the monitoring of the deformation induced by different extraction activities acted with regular frequencies.
Because SAR scenes cover large areas, InSAR analyses represent the unique techniques able to assess spatially extensive urban subsidence or uplift patterns.