Deformation Time Series Monitoring of Nisyros Volcano (Greece) During Unrest And Rest Period.
Derdelakos, Konstantinos1; Papageorgiou, Elena2; Parcharidis, Issaak1; Benekos, George1
1Harokopio University of Athens, GREECE; 2National Research Council of Italy, ITALY

The Hellenic Volcanic Arc, which stretches from Aegina and Methana in the west over Milos and Santorini and terminates at Kos and Nisyros in the east of Aegean Sea, is a result of northeastward-directed subduction (started around 4 Ma at the beginning of Pliocene) of the African plate beneath the Aegean microplate. Santorini volcano in the central sector of the arc and Nisyros in the eastern sector, are the two active volcanoes of the arc. Nisyros shows an unrest phase during 1996-97 accompanied by intensive seismic activity in the broader area at the beginning of 1996 and lasted through the end of 1997 and returned to the background level at the beginning of 1998. Spaceborne radar interferometry has already shown its ability in mapping ground deformation, like co-seismic deformation, as well as long-term movements as is the ground deformation in volcanoes, landslides and subsidence. This technique can be used to identify ground-surface deformation associated with movement of magma and/or hydrothermal fluids beneath volcanoes. Ground deformation monitoring is one of the main parameters that should be considered to assess volcanic hazard. In the current study the multi-reference synthetic aperture radar (SAR) interferometric technique was applied in order to study the evolution of ground deformation during the unrest period (1996-1997) and the post period of 2003-2010. Two different data sets of common acquisition geometry of radar scenes covering the mention periods were used. Specifically, SAR data obtained from ERS-1 & -2 and ENVISAT satellites were used with a total lifespan of 18 years. Concerning the unrest period 18 ERS-1 & -2 SAR SLC scenes in ascending orbit, 46 in descending covering the period of 1992-2001. For the rest period 27 ENVISAT ASAR SLC (ERS like) scenes in ascending orbit and 23 in descending covering 2003-2010. Due to the inability to find sufficient number of point-targets, natural or man-made, Persistent Scatterers Interferometry (PSI) technique failed to deliver acceptable results. Therefore, in order to reveal the deformation history Singular Value Decomposition (SVD) method was applied, allowing to measure ground deformation time-series on pixel basis.