DID THE GULF OF CORINTH OPENING OCCUR ON LARGE-OFFSET, LOW ANGLE NORMAL DETACHMENT FAULTS OR SMALLER-OFFSET, STEEPLY DIPPING NORMAL FAULTS?

Earthquake studies over the past 30 years have shown evidence for low-angle, north-dipping normal faults with dips of 5 to 30 degrees at a depth of 10 km controlling the long-term opening of the Gulf of Corinth (GOC) in Greece. The presence of low-angle normal faults have been challenged by other groups of seismologists who propose the low angle fault plane chosen may actually be the auxiliary plane and the active faults responsible for the present-day opening of the GOC are in fact smaller-offset, sets of normal faults with dips of 60-80 degrees. Some previous workers have also proposed that fault dips may have changed through time with an early phase of low-angle faulting following by a later phase of steeper faults. To resolve this controversy, I show mapping results of normal fault dips based on 1927 km of multi-channel seismic data collected in 2001 along with other published studies of faults in the on-shore and offshore areas in the GOC. The upward projection of the proposed low-angle, normal projects to the surface in a 5-km-wide area bounding the southern GOC although the upper 5 km of the fault projection is aseismic. On land studies show these faults which have much steeper dips at the surface (45-60) than their low-dipping down dip project inferred from earthquake studies. Compilation of offshore fault dips based on seismic lines shows three groups of faults: faults along the south coast uniformly dip northward at dips of 45° to 50°; faults in the center of the basin dip both north and south at dips of about 20° and about 50° and define a central horst block in the middle of the basin; faults in the north dip southward and are interpreted by most workers as being antithetic faults with smaller offsets than the main basin-controlling normal faults along the southern edge of the basin. Structural restorations are presented across the basin that are based on all faults dips measured or compiled in this study. These sections show limited extension and limited upper plate rotations and are therefore not supportive of larger extensions as expected for low-angle normal faults.