Kinematic Decomposition of Three Decades of Multi-Mission DInSAR Time Series Reveals Persistent Ground Deformation Geometry at Campi Flegrei Caldera

Understanding the spatio-temporal structure of ground deformation in caldera systems remains a major challenge because multiple processes may coexist and interact across different spatial and temporal scales. The Campi Flegrei caldera provides an exceptional natural laboratory to investigate these dynamics through long-term geodetic observations. Here, we integrate three decades of multi-mission Differential Interferometric Synthetic Aperture Radar (DInSAR) data to retrieve the spatio-temporal evolution of the ground displacement field. We analyse the resulting dataset using a kinematic decomposition in which the deformation field is expressed as the sum of (i) a time-invariant spatial pattern modulated by a time-dependent amplitude and (ii) a spatially variable constant-velocity component. Our results show that the observed deformation is largely governed by a dominant spatial pattern that remains remarkably stable through time, while its temporal amplitude reproduces both subsidence and uplift phases. In addition, a secondary constant-velocity component, with amplitudes of only a few mm yr−1, is required to account for residual spatial variability, particularly in the south-eastern sector of the caldera. A transition in deformation behaviour around 2012–2013 is associated with a south-westward expansion of the dominant deformation pattern. The inferred dominant spatial patterns are consistent with a persistent deformation source located at a depth of approximately 3–4 km, whereas the secondary spatially variable constant-velocity field is compatible with a deeper expansion process. These findings indicate that long-term caldera deformation can be effectively represented within a low-dimensional kinematic framework. This approach provides a robust basis for the interpretation of geodetic time series and for the identification of changes in deformation regime in restless caldera systems.