New constraints on active normal faulting in the South Gulf of Evia, Greece

In many areas of active faulting, the continuity of normal faults with a short or incomplete historical earthquake record and subtle topographic expression is not fully understood: as a result the seismic potential of these faults is often underestimated. The Southern Gulf of Evia rift, Greece is an example of a poorly explored normal fault bounded system, where the location and spatiotemporal evolution of the major basin bounding faults is not well constrained. We integrate geomorphic and structural field data, topographic analyses and geodetic data to constrain the locations, footwall geometries and structural evolution of 8 major extensional structures bounding the Southern margin of the South Gulf of Evia. We propose that this fault system comprises two isolated fault groups containing both partially and fully linked segments. These fault linkage scenarios suggest that the eastern fault group may have a total linked length of ca. 40 km with a maximum credible earthquake size of Mw 7.0. Further, we reconcile new analysis of vintage sparker seismic reflection data previously acquired and interpreted in the 1980s, with onshore geomorphic indicators of tectonic uplift to provide new constraints on the continuity of active normal faults offshore, including the major normal fault zones bounding the northern margin of the rift. By comparing our reconstructions of footwall relief with the seismic reflection and Ocean Bottom Seismometer (OBS) data, we suggest footwall uplift to hanging wall subsidence ratios of 1:2-1:3 and total slip rates in the order of 2-3 mm/yr. Finally, based on the correlation of seismic stratigraphy with a global eustatic sea level curve and a comparison of estimated sediment fluxes into the Gulf with measured sediment volumes in the South Gulf, we propose updated Pleistocene-Holocene ages for the basin stratigraphy and suggest possible timescales for fault evolution and linkage along the rift margins.