New results on the contemporary plate tectonics in the Aegean region from seismological investigations

Abstract

The morphology of the Hellenic Wadati-Benioff zone and of the seismically active fracture zones in the overlying continental wedge is considered in this study. Comparative analysis of our previous results on seismogenic properties like seismic activity, energy and b-value, 3-D P-wave velocity anomaly patterns and the stress field distribution in the Aegean region imply that the physical conditions in the E and W parts of the region are different. Evidences for heated material in the eastern part of the region stem from a large low velocity anomaly around Rhodes island at depths 50–150 km. Further indications are: the delayed start of the present subduction cycle, upper boundary of the seismic gap at about 50 km shallower, relatively few earthquakes and moderate seismic energy release. In addition, in the deepest part of the eastern flank we have relatively high seismic activity, high b-value and low energy release. The stress pattern in the Aegean shows that the convergence between the African and the Eurasian plates is in the SW-NE direction. The stress regime in the Hellenic Wadati-Benioff zone indicates that the major forces which dominate the contemporary plate tectonics in the region are the SW-NE convergence between the African and Eurasian plates, the loading of the overriding plate onto the sinking one and the slab pull. The impact of these forces on the subduction process changes with depth - the slab pull increases while the others decrease. Two additional forces involved in the geodynamics of subduction are a W-E shortening of the 40–80 km layer in the western subduction flank due to interaction of the slab with the Apulian platform and a horizontal compression trending north in the deepest portion of the eastern flank. The latter is related to interaction with heated mantle material. The geometry of the seismically active deep structures influences the space distribution of the stress field which has the role of channeling the maximum or minimum compressive stresses.