Multiple causes of ground deformation in the Napoli metropolitan area (Italy) from integrated Persistent Scatterers DinSAR, geological, hydrological, and urban infrastructure data

Abstract

This study presents a Differential SAR Interferometry (DinSAR) analysis and review of ERS (1992–2001) and Radarsat (2003–2007) data on the city of Napoli (Italy). These data are processed using the Persistent Scatterers Interferometric synthetic aperture radar (PSInSAR) technique and post-processed by statistical selection and filtering with the aimto obtain, by combining ascending and descending geometries, the spatial distribution of the vertical and horizontal (east–west) components of the ground displacement velocity.We identify fivemain areas of subsidence affecting residential districts and strategic infrastructures (transportations and industrial plants). These are: a) Vomero–Arenella district; b) Scudillo–Stella district, c) Municipio Square; d) Garibaldi Square; and e) Poggioreale district. In these areas, the ground deformation rate is between −1.3 and −10.5 mm/yr and varies through time. In particular, in the investigated time period, the subsidence rate (i) persistently increases in the Scudillo–Stella and Poggioreale districts, (ii) abruptly increases in correspondence of underground construction activities (Municipio and Garibaldi squares), and (iii) decreases following the ground deformation style of the Campi Flegrei caldera (Vomero–Arenella district). More restricted areas of subsidence also occur in the northeastern, less urbanized, sectors of the Napoli metropolitan area. The subsidence triggering factors are investigated through a reviewof the available geological geomorphological, hydrological, and urban network information. With respect to other urban contexts, where the cause of subsidence is of natural or anthropogenic origin, Napoli shows a multiple association of triggering factors. These factors are: sub-soil excavations for the construction of transport infrastructures, filling/emptying cycles of large underground water reservoirs, gravity instability related to local morphological factors, raise of the water table with consequent hydrocompaction due to the stop of ground water withdrawal, and re-activation of volcano-tectonic faults associated to the uplift and subsidence phases (bradyseism) of the neighboring, active Campi Flegrei caldera, whose western sector includes a part of the Napoli urban area. We conclude that in a complex urban and geological setting like that of Napoli, ground deformations induced by anthropic and natural processes may coexist and should be monitored for a correct evaluation of the associated hazard and the management of the city planning activities. Finally, the combined review of satellite and geological data available for different urban districts worldwide is essential to identify the sources of ground deformation and analyze the time evolution of the related anthropic and/or natural processes.