The strain field in northwestern Greece and the Ionian Islands: results inferred from GPS measurements

Recent crustal movements detected by the analysis of repeated satellite geodetic measurements reflect the ongoing geodynamic processes in the Alpine-Mediterranean area. Superimposed on the large-scale counterclockwise rotation of the African plate, complex dynamic processes are affecting the lithospheric fragments between the African and Eurasian plates. Key features to better understand the driving forces and associated seismic activity in the Africa/Eurasia collision zone are the Calabrian and Hellenic arcs. In this paper geodynamic investigations along the West Hellenic arc are discussed. They are based on two epochs (1989 and 1993) of satellite geodetic measurements carried out using the US Global Positioning System (GPS). The results are presented in terms of relative displacements and strain rates. Within the time span of 4 years southwestern Greece has moved to the southwest relative to southeastern Italy by an average of 120 mm, increasing from 80 mm at Lefkada, in the center of the Ionian Islands, to 160 mm at the Peloponnesus. The maximum strain rate is 0.18 μstrain/a located in the vicinity of Lefkada, where anomalously high earthquake activity is observed. The data provide strong evidence for dextral strike-slip motion on the order of 25 mm/a along the Kephalonia Fault Zone (KFZ). The deformation field of the KFZ is interpreted as a transition zone between the kinematics of the Apulian platform and the West Hellenic fold and thrust belts.