Combined Seismicity Pattern Analysis, DGPS and PSInSAR studies in the broader area of Cephalonia (Greece)

Abstract

Ground deformation studies based on Differential GPS (DGPS) measurements and Permanent Scatterer Interferometric (PSI) analysis have been conducted on the islands of Cephalonia and Ithaca covering the period 1992 to 2010. DGPS measurements for the period 2001 to 2010 revealed horizontal clockwise rotation of Cephalonia and velocities ranging from 3 to 8mm/yr with the largest values occurring at the western and southern parts of the island. Considering its vertical deformation, two periods are distinguished on the basis of DGPS and PSI: The first one (1992 to 2003) shows generally an almost linear slight subsidence (around 1mm/yr) which is consistent with expected neotectonic movements of the island. The second one (2003 to 2010) has been tentatively attributed to dilatancy in which reversal to uplift (2–4mm/yr) occurred mainly along the southern and southeastern parts of the island, while larger magnitudes (>4mm/yr) took place at the western part. These non-linear high rates of uplift started at about mid-2005, and were of increasing rate at the southern part, but of decreasing rate at the western part; they may indicate a major regional crustal deformation process in an environment that has previously supported offshore large magnitude earthquakes. Parallel analysis of the observed seismicity in the broader area identified two seismically critical areas on the basis of the decelerating–accelerating seismicity: a major one south of Cephalonia and west of Zakynthos, and another minor one at the NW part of Peloponnese. Critical time estimates of the occurrence of a future strong seismic event in the above critical areas were also made based on: (i) accelerating seismicity, and (ii) the temporal analysis of the seismicity.