*Article* **Multi-Sensor SAR Geodetic Imaging and Modelling of Santorini Volcano Post-Unrest Response**

**Elena Papageorgiou 1, Michael Foumelis 2,\*, Elisa Trasatti 3, Guido Ventura 3, Daniel Raucoules <sup>2</sup> and Antonios Mouratidis <sup>1</sup>**


Received: 25 December 2018; Accepted: 24 January 2019; Published: 28 January 2019

**Abstract:** Volcanic history of Santorini over recent years records a seismo-volcanic unrest in 2011–12 with a non-eruptive behavior. The volcano deformation state following the unrest was investigated through multi-sensor Synthetic Aperture Radar Interferometry (InSAR) time series. We focused on the analysis of Copernicus Sentinel-1, Radarsat-2 and TerraSAR-X Multi-temporal SAR Interferometric (MT-InSAR) results, for the post-unrest period 2012–17. Data from multiple Sentinel-1 tracks and acquisition geometries were used to constrain the E-W and vertical components of the deformation field along with their evolution in time. The interpretation of the InSAR observations and modelling provided insights on the post-unrest deformation pattern of the volcano, allowing the further re-evaluation of the unrest event. The increase of subsidence rates on Nea Kameni, in accordance with the observed change of the spatial deformation pattern, compared to the pre-unrest period, suggests the superimposition of various deformation sources. Best-fitting inversion results indicate two deflation sources located at southwestern Nea Kameni at 1 km depth, and in the northern intra-caldera area at 2 km depth. A northern sill-like source interprets the post-unrest deflation attributed to the passive degassing of the magma intruded at 4 km during the unrest, while an isotropic source at Nea Kameni simulates a prevailing subsidence occurring since the pre-unrest period (1992–2010).

**Keywords:** volcano deformation; SAR interferometry; post-unrest deflation; inversion modelling; Santorini
