Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms

Abstract

Fault plane solutions for earthquakes in the central Hellenic arc are analysed to determine the deformation and stress regimes in the Hellenic subduction zone in the vicinity of Crete. Fault mechanisms for earthquakes recorded by various networks or contained in global catalogues are collected. In addition, 34 fault plane solutions are determined for events recorded by our own local temporary network on central Crete in 2000–2001. The entire data set of 264 source mechanisms is examined for types of faulting and spatial clustering of mechanisms. Eight regions with significantly varying characteristic types of faulting are identified of which the upper (Aegean) plate includes four. Three regions contain interplate seismicity along the Hellenic arc from west to east and all events below are identified to occur within the subducting African lithosphere. We perform stress tensor inversion to each of the subsets in order to determine the stress field. Results indicate a uniform N-NNE direction of relative plate motion between the Ionian Sea and Rhodes resulting in orthogonal convergence in the western forearc and oblique (40–50∘) subduction in the eastern forearc. There, the plate boundary migrates towards the SE resulting in left-lateral strike-slip faulting that extends to onshore Eastern Crete. N110∘E trending normal faulting in the Aegean plate at this part is in accordance with this model. Along-arc extension is observed on Western Crete. Fault plane solutions for earthquakes within the dipping African lithosphere indicate that slab pull is the dominant force within the subduction process and responsible for the roll-back of the Hellenic subduction zone.