Abstract:
Results from the application of Persistent Scatterers Interferometry in Lisbon Metropolitan Area revealed two
previously unknown subsiding urban areas: one (Laranjeiras) is located in the center of Lisbon; another
(Vialonga) is to be found toward the North, in an industrial region crossed by Lisbon's main highway and
railway lines. The two subsiding sectors are bordered by sharp velocity gradients, and the subsidence pattern
appears partially delimited by mapped geologic faults. Surface geology and urbanization alone are unable to
explain the phenomena. In the Vialonga area, the historical record of water pore pressure shows a clear
decline of the levels (up to 65 m in 27 years), providing evidence of over-exploitation of groundwater
resources. Limited information from wells drilled inside and outside the subsidence area points to a spatial
correlation between the subsidence and the water pressure levels, and suggests that faults could be acting as
hydraulic barriers in the aquifer system. The surface subsidence detected is probably caused by compaction of
a clay-rich Oligocene-aged aquitard, led by over-exploitation of adjacent aquifers. The same Oligocene
aquitard layer is present in the Laranjeiras area, immediately bellow a multi-layered sand–clay–limestone
Miocene aquifer, but further work is needed to diagnose the possibility of over-exploitation of groundwater
here. In this work we were able to independently confirm the PSI results, by comparing autonomous PSI
results processed for the same geographical areas, and by comparing PSI with leveling and continuous GPS
derived subsidence velocities, whose close match provided further ground validation of the space-borne PSI
technique.
© 2011 Elsevier Inc. All rights reserved
