We present three studies about earthquake interactions and the nucleation phase of big earthquakes. The first part of this work deals with the northwestern Turkey, where two tectonic regimes exist, with the transform North Anatolian Fault and extension clusters around it. We show that these two systems interact, but respond differently to Izmit earthquake (1999) stimulation. Computations of the Coulomb stress changes induced by the Izmit earthquake indicate that strike-slip events respond to dynamic stresses, whereas the extension ones seem to be controlled by the static deformation of the crust. In the second part, we analyze a seismic sequence that occurred in 2008 in Greece. This analysis shows that subduction or strike-slip earthquakes of the sequence depict the overall motion of the southwestern Greece to the SSW, accompanied by the plunge and the southward retreat of the slab. This first deformation stage is followed, few months later, by the internal deformation of the Aegean plate, which occurs as N-S extension. This seismic sequence depicts the existence of dynamic coupling between the Hellenic subduction and the prolongation of the North Anatolian Fault. The aim of the last part was to shed some lights on the question: is there a systematic seismic phenomena preceding the occurrence of big earthquakes? To do that, we studied seismic activity preceding M≥6.5 earthquakes in some well-instrumented areas of the North Pacific. We show that most of the interplate earthquakes are preceded by an increase of the activity, unlike the intraplate ones. We also highlight a different behavior between strike-slip and subduction events: foreshocks of subduction earthquakes are located in a large area, preventing a cascade triggering.
