Seismic structure and the active Hellenic subduction in the Ionian islands

In the region of the Ionian Islands of western Greece, the active margin of the Hellenic domain passes from oceanic subduction in the south to contine ntal collision in the north, linked by the right-lateral Cephalonia transfo rm fault. A slightly landward dipping interface revealed at 13 km depth by a single previous line in the channel between Cephalonia and Zante has been suggested as the interplate subduction boundary. New marine multichannel r eflection profiles and OBS refraction and wide-angle reflection data confir m the reflector as a regional feature. These data evidence its extension to the south, where large, low-angle thrust earthquakes occur offshore to Zan te. The new profiles establish a coincidence between the focal depths of th ese large subduction events and the imaged bright reflective level, confirm ing its tentative interpretation as the interplate boundary, which generall y appears with a positive reflection polarity. In this context, the Ionian Islands outcrop corresponds to a shallowing of the interplate boudary from south to north. Ln the south, offshore Zante, the interplate boundary compr ises a stratified zone that may be considered as the sedimentary cover of t he Ionian Basin oceanic-like crust, which forms the lower plate hen. The sh allower position and single-cycle reflection character of the interplate fu rther north suggest that the lower plate could there be the Apulian paleoma rgin to that basin. (C) 2000 Elsevier Science B.V. All rights reserved.