Seismicity Properties as a Marker of the Active Plate Convergence in the western Hellenic Arc

The western Hellenic Arc is one of the most seismically active regions in the western Eurasia. Large, shallow and intermediate depth earthquakes take place there with maximum magnitudes up to 7.5 occurring around Kythira isl. between Peloponnese to the north and Crete isl. to the south. This is also supported by historical seismicity data which indicate that some of the large shocks were tsunamigenic, that is very possibly they were associated with dip-slip faulting. In the north section of the western Hellenic Arc, particularly between Zakynthos isl. and Peloponnese, the upper bound of earthquake magnitude appears to be relatively low not exceeding 6. This is attributed to the high degree of crustal heterogeneity as seismological, sedimentary and tectonic data imply. However, the highly heterogeneous structure of the seismogenic layer favours the incidence of foreshock activity. The lateral distribution of large earthquake rupture zones, the spatial distribution of moderate and low magnitude earthquakes as well as focal mechanisms are used to improve the delineation of the active plate margin in the region. The result is independently examined from bathymetry and field observations regarding evidence of active faulting on land. Additional evidence comes from the propagation field of strong historical tsunamis. Volcanism is not existant in the western Hellenic Arc in contrast to the central and eastern segments of the Arc. This is possibly interpreted by the relatively more shallow position of the foci of large intermediate depth earthquakes which does not favour melting of the upper mantle material.