New constraints on the activity and evolution of the young Aigion-Erineos Fault System, Gulf of Corinth, Greece

The study of young active faults provides an important opportunity to constrain the early phases of fault growth and linkage. In addition, such structures often pose an underestimated seismic hazard as they can have limited geomorphic and structural expression. The Aigion - Erineos fault system (AEFS) is a young active normal fault on the south coast of the Gulf of Corinth rift zone in Central Greece that provides a key link between the Gulfs of Corinth and Patras. However, significant uncertainties remain regarding the key characteristics of this fault system, including its geomorphic expression, throw, slip rate, age and the degree to which its constituent fault segments are linked. Here we combine geomorphic field observations and structural measurements, DEM and topographic analyses, short-interval ground motion data, and offshore seismic data to produce the most complete characterisation of the AEFS to-date. Our findings show a complex geomorphic expression of the AEFS with 5 active fault segments, arranged in an en-echelon structure and partially to fully linked together. We show the Aigion Fault segment (AF) has an initiation age of 200-240 ka, but there has been a significant increase in slip rate since 80 ka.  Consequently, we suggest the AF has a slip rate of ca. 5-6 mm/yr, greater than the time-averaged rate estimated by McNeill et al., 2007 of 3.5 ± 1 mm/yr. Data from the European Ground Motion Service (EGMS) illustrate that the field derived fault traces of the AEFS correspond closely with an abrupt, linear transition from uplift to subsidence seen from satellite measurements, suggesting the possible presence of ongoing aseismic deformation. The three fault segments to the west of the AF (the Fassouleika, Selianitika, Erineos segments) are suggested to have initiated after 80 ka and may be as young as 25 ka and are now partially to fully linked with the AF. We obtain maximum slip rates for these segments of between 5 and 9 mm/yr. To the east an offshore fault segment is likely to be soft-linked with the AEFS and has a well constrained slip rate of 2.7 mm/yr through the Holocene. Our results suggest the linked fault system has a total length of ca. 20 km, with a potential maximum credible earthquake size of Mw = 6.6.