The Kefalonia Transform Fault: a STEP in the making

Vertical tears in subducted slabs have recently been recognized in the majority of the global subduction zones. Surprisingly, the slab tears evolved into Subduction-Transform-Edge-Propagators (STEPs) in only very few regions, i.e. the conditions under which STEPs form are special. The presence of a vertical tear in a slab seldom leaves a clear tectonic imprint in the crust of the overriding plate. This is different for STEPs: their footprint in the tectonics of the Mediterranean and Pannonian basins attest to the relevance of STEP activity. It is therefore relevant to constrain the conditions that facilitate STEP initiation. We therefore study a candidate region for STEP initiation in the western Hellenic Subduction Zone: Govers and Wortel (2005) suggested that the offshore Kefalonia Transform Fault and its on-land continuation constitute a STEP Fault, which inspired regional studies of the geometry of the shallow (50-200 km depth) slab, but none of these were conclusive.