Magnitude and causes of long-term subsidence of the Po Plain and Venetian region

In the Po Plain (Northern Italy), the natural component of subsidence can be split into: (1) a long-term component controlled by tectonics and geodynamics, active on time periods of about 106 yr; (2) a shortterm component, controlled by climatic changes (glacial cycles), acting on periods of 103-104 yr, plus sediment compaction and loading of deltas. The magnitude of the long-term component of subsidence in the Venetian coastal area has been estimated using stratigraphic data from industrial wells. Thickness and absolute age of the Pleistocene base allow the calculation of long term subsidence rates of about 1.0 mm yr-1. Long term subsidence in the Venice area and in the Po Plain is triggered by the flexure of the Adriatic plate subducting under the Apennines, as suggested by the interpretation of the CROP M-18 seismic line. Analysis of 14C ages of recent sediments provides a constraint on total natural subsidence rates in the area of Venice, with average values of around 1.3 mm yr-1. The deglaciation component is therefore limited to some 0.3 mm yr-1. It is concluded that the most significant part of the natural subsidence of the Venetian coastal area is related to the north-eastward retreat of the Adriatic subduction, a process inducing subsidence in the whole Po Plain basin and part of the Alps.