Seismic hazard scenarios from the longest geologically constrained active fault of the Aegean

Abstract

Several seismic hazard scenarios are examined concerning the seismic potential of the North Aegean Basin (NAB), based for the first time purely on geological data. Detailed analysis of the bathymetry incorporated by seismic reflection profiling has recently revealed the neotectonic structure of the NAB and demonstrates that the dominant structure is a 160 km long NE–SW trending fault, comprising of four major segments. This is the longest geologically constrained active fault in the Aegean Sea. Following deterministic fault specific analyses, six major seismic sources are identified. Firstly, a ∼55 km oblique normal fault segment towards the southwestern end of the basin, that can accommodate a M=7.1 event. Such an event could produce a maximum vertical offset up to 3–4 m posing also a tsunami threat. Based on geological data a minimum throw rate of 1.2±0.2 mm/yr is estimated for this segment, implying a recurrence interval of 1100±350 yrs. Secondly, a sub-vertical ∼70 km long, E–W dextral trending shear zone northwards the southwestern corner of the N. Aegean basin that can generate a M=7.2 strike–slip event. Sources 3 and 4 towards the central and eastern segment of the fault are expected to produce seismic strike slip events of M=7.1, whereas the fifth source suggests the simultaneous activation of sources 3 and 4, producing a 105 km long rupture and a M=7.4 event. Finally, the sixth source implies a multi-segment rupture involving the entire 160 km long south marginal fault, producing a M max=7.6, which represents the worst-case scenario. This value limits all uncertainties posed on the maximum expected magnitude by other published estimates (ranging from M=7.2 up to 8.5) that are based solely on seismological and/or geodetic approaches.