EARTHQUAKE MECHANISMS OF THE ADRIATIC SEA AND WESTERN GREECE - IMPLICATIONS FOR THE OCEANIC SUBDUCTION-CONTINENTAL COLLISION TRANSITION

We present 21 focal solutions (magnitude >5.5) reliably computed by bo dy-wave modelling for the western Hellenic are from Yugoslavia to the southern Peloponnese. Mechanisms located within the Aegean show normal faulting, the T-axis trending N-S in the centre and parallel to the a ctive boundary in the external part. Mechanisms associated with the Ke ffalinia fault are consistent with dextral strike-slip motion. Reverse mechanisms located along the active boundary are remarkably consisten t and do not depend on the nature of the active boundary (continental collision or oceanic subduction). The consistency in azimuth of the sl ip vectors and of the GPS velocity relative to Africa, all along the a ctive boundary, suggests that the deformation is related to the same m otion. The discrepancy between seismic-energy release and the amount o f shortening confirms that the continental collision is achieved by se ismic slip on faults but the oceanic subduction is partially aseismic. The northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent e volution of the active subduction.