Subsidence of Campi Flegrei (Italy) detected by SAR interferometry

Seven ERS SAR images of the Napoli area acquired from 1993 to 1996 were used to create six differential interferograms. Although the ambiguity height of the selected couples is high, because of the adverse characteristics of the area, the interferograms exhibit a relatively low level of coherence, even for couples sampling short time intervals. According to the estimated accuracy, no deformation is observed on Vesuvio volcano. The best interferogram, corresponding to the period Feb. 14, 1993 - Apr. 3, 1996, shows that the centre of the Campi Flegrei caldera, near Pozzuoli harbour, subsided by about three fringes (84 mm) during the three years interval. This result is consistent with the value of 28 +/- 2 mm/year obtained from routine levelling surveys over the same period in the same area. The deflation that started after the 1983-1984 seismic and inflation crisis is thus still significant. The modelling of the fringe pattern, assuming a spherical deflating source within an elastic half-space medium, predicts a source centred about 800 m Southwest of Pozzuoli at a depth of 2.7 +/- 0.3 km. For the studied time window, the maximum subsidence predicted by the model is 25 mm/year.