Nisyros Island is a Quaternary composite volcano located close to the eastern termination of the South Aegean Volcanic Arc. Large destructive earthquakes have been reported in the study area. Nevertheless, seismic activity during the last decades is moderate to low, consisting of both shallow and intermediate depth earthquakes. The main regions of the broader area with observed spatiotemporally clustered seismicity are between Nisyros and Karpathos, east of Kos and in the gulf of Symi. Major events of intermediate depth have occurred near Karpathos and Rhodes Islands while the most significant zone of deep earthquakes is identified in the western Nisyros basin. Evidence for a non-systematic temporal co-incidence of deep events at different regions as well as increase in shallow seismicity after the occurrence of a strong deep event have been observed. Moment tensor inversion , using recordings in local and regional distances, was applied to determine the focal mechanisms of recent moderate events. The solutions, obtained by minimizing the difference between observed and synthetic waveforms, revealed that shallow events are mainly related to normal faulting, whereas intermediate depth events to reverse faulting with important strike-slip component. A tomography study was performed, using manually located events, and identified two areas of high V _p/V _s ratio and low velocity perturbations. The first is located SW of Nisyros and can be attributed to magma intrusion of deeper composition containing fluids and melts. The second, reaching 15 km depth, is possibly related to the magmatic chambers that feed the Yali and Strongyli volcanic centers.