Comparing geological and Persistent Scatterer Interferometry data of the Sele River coastal plain, southern Italy: Implications for recent subsidence trends

Many coastlines around the world are subsiding, often due to tectonic causes. In tectonically active areas, the exploitation of natural resources has caused acceleration of subsidence rates. In these cases, it is difficult to separate the many different components of the subsidence process. We try to fill this gap, using both remote sensing data and geological evidence, in an area located in southern Italy (Sele River plain) and characterized by the presence of both human activities and natural processes.The coastal sector of the Sele plain shows a complex subsidence pattern, as testified by Persistent Scatterer Interferometry (PS InSAR) data related to a period of about two decades (1992-2010), that we put in correlation with stratigraphical data from both outcrops and boreholes (ca. 250). The Quaternary infill of the coastal sectors of the plain is not laterally isotropic and homogeneous because of the presence of layers of clastic sediments with different degrees of compaction. Dunal and beach sands, back-ridge (lagoonal and palustrine) silty clays, palaeosols and thick peaty layers are the main facies of this sedimentary prism. The back-ridge depressions hosted palustrine and marshy environments and were artificially drained in the last centuries. The main output of the PS-InSAR analysis is a map of vertical ground deformation (VGD), which has been a useful tool to understand the causes of the subsidence process if combined with geological data from field and boreholes. In fact, the overlay of the SAR interferometry VGD map with the geomorphological and stratigraphical features shows that the subsidence is higher in the northern sector of the plain, where the Quaternary alluvial-coastal deposits are thicker because of the structural asymmetry of the graben. The maximum subsidence rate, however, can be observed in the central part of the plain, in correspondence of the Sele, Tusciano and Picentino river mouths and in the coastal belt. This could be related to the thickness of loose sediments (>20 m) and to the presence of still compacting clay-rich sediments. In the southernmost sector the rates are the lowest recorded in the plain due to the minor thickness of Holocene deposits and to the presence of very thick sedimentary bodies of travertine. The understanding of subsidence patterns may represent a basic tool for future studies about the assessment of the coastal inundation hazard and related risk mitigation in the Sele River plain. Such a tool may reinforce the methodological approach to risk assessment in similar morphological settings. (C) 2019 Published by Elsevier B.V.