Seismotectonics of the northern Aegean area

Abstract

Data concerning the focal mechanism and the spatial distribution of earthquakes have been used to investigate the active tectonics of the northern Aegean and the surrounding area. A thrust region, which includes the northernmost part of the Aegean and at least part of the Marmara Sea, has been defined. An amphitheatrical Benioff zone dipping towards the thrust region from south, east and probably from west, at a mean angle of about 30°, has been detected. The thrust region is surrounded by a region of normal faulting. An eastward progression of the seismic activity in this normal faulting region between 1954 and 1971 has been observed. A correspondence between the earthquake occurrence in the thrust and normal faulting regions has also been observed. Each large shock produced by tensional mechanism in the region of normal faulting is preceded or followed by one or more shocks of compressional mechanism in the thrust region. The focal mechanism, the distribution of the earthquake foci with intermediate focal depth, as well as some magnetic and gravimetric observations can be interpreted by assuming that dense oceanic crust sinks in the northern part of this area and that the adjacent lithosphere moves by segmentation to fill the void with the consequence of producing tensile stresses associated with normal faulting. Such a mechanism of lithospheric interaction suggests that accretion probably takes place in this area.