New Constraints on Active Normal Faulting in the South Gulf of Evia, Greece: Geometry, Evolution, and Seismic Hazard of the South Coastal Fault System

Abstract In many areas of active faulting, the continuity of normal faults with short or incomplete historical earthquake records and more subdued topographic expressions is not fully understood and consequently the seismic potential of these faults is often underestimated. One example of a poorly understood normal‐fault bounded system is the South Gulf of Evia rift, Greece, where the location and evolution of the major basin bounding normal faults is not well constrained. We integrate geomorphic and structural field data, including the documentation of uplifted marine terraces, wavecut notches and beachrock, with topographic analyses, geodetic data and analysis of river long profiles to constrain the locations, footwall geometries and structural evolution of 8 active normal faults bounding the Southern margin of the South Gulf of Evia. By combining these data sets we resolve vertical ground motion and fault growth over a range of timescales from 10 5 –10 6 yrs to the past 12 kyrs. We propose that this fault system is formed of two fault groups comprised of both partially and fully linked segments. By comparing reconstructions of footwall relief with previously interpreted sparker seismic reflection and OBS data in the eastern offshore region of the Gulf, we suggest total slip rates in the order of 2–3 mm/yr for the eastern faults. These fault linkage scenarios suggest that the western faults may have a total linked length of ca. 20 km, whilst the eastern faults may have a total linked length of ca. 43 km with a maximum credible earthquake size of Mw 7.0.