Recent kinematics of Crete, observed by InSAR, reveal complex, curved-forearc deformation and aquifers changes

Located on the overriding plate of the Hellenic subduction margin, the 250 km-long island of Crete offers a unique opportunity to study curved-forearc deformation. The African-Eurasian plate-convergence of ~40 mm/yr (~80 %) is primarily accommodated aseismically, but intense seismicity is recorded at the plate-interface and a reverse splay faults along the Hellenic trough; frequent M6+ earthquakes and (at least one) tsunami-genic event, causing up to 10 m of paleoshoreline uplift in western Crete, are reported. Global Navigation Satellite System (GNSS) data revealed N-S shortening of ~2 mm/yr within western Crete due to pure plate convergence. Further east, the curved subduction trench accommodates increased oblique slip, causing E-W extension of ~2 mm/yr in eastern Crete.

Recently, the European Ground Motion Service published dense InSAR surface deformation data in East and Up direction of whole Europe. The InSAR time-series comprise positioning samples every six days, respectively, every ~50 m, and, in Crete, exhibit long-wavelength deformation signals caused by deep-rooted, tectonic sources that are overlaid by (often seasonally-modulated) signals originating in shallow aquifers. We analyze these time-series in space and time and validate the results using available GNSS rates, a seismic catalog and an active fault data base. Preliminary results suggest a slight eastward tilt of Crete, which is not confirmed by published GNSS rates, and has to be investigated further. Spatially-confined uplift of up to ~5 mm/yr are observed at the karstic Omalos plateau, and up to ~30 mm/yr subsidence in the Messara basin, both probably related to groundwater replenishment/abstraction. Relative eastward motion increases towards eastern Crete, particularly in the fault zones embracing Mirabello bay and east of it, thus confirming the aforementioned E-W extension, and towards the southern coast.