Space and time distribution of the intermediate focal depth earthquakes in the Hellenic arc

Abstract

Accurately determined focal coordinates of earthquakes which occurred in the Hellenic arc between 1964 and 1979 have been used to check the suggestion made ten years ago for a Benioff zone in the Hellenic arc. These recent data leave no doubt that the foci of the intermediate focal depth earthquakes in the Hellenic arc form a well-developed Benioff zone of amphitheatrical shape which dips from the convex (eastern Mediterranean) to the concave (Aegean) part of the arc. Evidence, based on the time distribution of the intermediate focal depth earthquakes in the Hellenic arc during the last two centuries, indicates that this deep seismic activity follows a periodic pattern. Quiescence periods of the order of six decades are followed by very active periods of about two decades. If this periodicity, which seems to be compatible with recent ideas on the deep tectonics of the area, is true, a new period of high-rate intermediate focal depth activity is expected to break in about twenty five years.