Surface deformation analysis in Northeast Italy by using PS-InSAR and GNSS data

In the present study, we exploited the potential of satellite-based geodetic data for detecting and measuring surface displacement in Northeast Italy. In this contest, we focused mainly on 1) the estimation of the interseismic deformation during the satellites’ observation period, 2) the detection and analysis of the main deformation patterns, and 3) the correlation of the signals to the active tectonic structures. Despite the low convergence rates (~ 1.5-3 mm/yr), Northeast Italy is an active tectonic area, as testified by the instrumental and historical seismicity. The Adria-Eurasia convergence is mainly accommodated by the thrusts and strike-slip faults of the Southeastern Alps and the External Dinarides, located in the northern and northeastern sectors of the study area. The Venetian-Friulian plain and the Adriatic coasts, affected by active subsidence, dominate the southern region. We used the Stanford Method for Persistent Scatterers (StaMPS) applied to Sentinel-1 SAR images acquired along the ascending and descending orbit tracks between 2015 and 2019. Based on a stack of single-master differential interferograms, we detected coherent and temporally stable pixels based on amplitude and phase noise analysis. After applying spatial-temporal filters and additional post-processing operations to refine the measurements, we used Adria-fixed GNSS velocities derived by permanent stations in the study area to calibrate the InSAR velocities. The outcome consists of Line-OF-Sight (LOS) mean ground velocity maps derived by displacement time series along the radar directions for each satellite track. The combination of the LOS datasets yields vertical and east-west velocity maps, which are mostly in agreement with GNSS data and previous geodetic studies. Based on our measurements, we observe a significant positive velocity gradient of 1 mm/yr across the westernmost sector of the Alpine system, suggesting an aseismic motion of the root of the Bassano-Valdobbiadene thrust. The positive vertical gradients (~1 and up to 2 mm/yr) across the Alpine-Dinaric systems in the central and eastern sectors and the eastward motion that increases northeastward (1-2 mm/yr) may be related to the active Alpine-Dinaric thrusts and strike-slip faults. We also suggest that the detected westward motion of the Friulian plain (around Udine) might be attributed to the presence of tectonic structures characterized by transcurrent-transpressive kinematics. Finally, we detect other signals, such as the significant subsidence (2-4 mm/yr) along the coasts and on the southern Venetian-Friulian plain, confirming the correlation between subsidence and the geological setting of the study area. In conclusion, our study confirms the potential of MT-InSAR and GNSS data for the estimation of the surface deformations in response to active tectonics, even in areas characterized by low deformation rates, such as Northeast Italy.