Seismicity and active faulting around the metropolitan area of Athens, Greece

The existence of active faults near large cities poses significant risk to the life and property of its inhabitants as well as to its public infrastructure. Here, we investigate the interplay between seismicity, active faulting, and interseismic strain accumulation within a radius of ∼ 50 km from the metropolitan area of Athens, the capital of Greece. We find that during the period 2011–2018, a total of 4722 earthquakes were recorded, the majority of which had local magnitudes < 3:0 with only four events being of moderate magnitude (M_L 4.1– 4.3). Precise relative locations with horizontal and vertical errors of ≤ 1 and 2 km, respectively, were obtained for 2666 of these events using the double-difference algorithm. Earthquake relocation was compared to the surface traces of 31 active and 49 “less-active” normal faults drawn from high-resolution (∼ 5 m pixel size) digital elevation models and complemented by analysis of geodetic data from 30 permanent Global Positioning System (GPS) stations. Joint analysis of these datasets suggests that microseismicity mostly clusters along the “less-active” faults, whereas the faults associated with impressive postglacial scarps (indicating recent activity) and historic seismicity are mostly quiet. Interestingly, GPS data indicate that both fault types currently accumulate elastic strain that ranges from 0.5 to 2.3 mm/yr. Based on their estimated rupture area, more than half of the recorded faults (N 54) are capable of generating earthquakes with moment magnitudes between 6.0 and 6.6. Although some of these sources are characterized by impressive postglacial scarps, many others have long earthquake recurrence intervals (i.e., have not ruptured during the past ∼ 16 ka) and are associated with intense microseismicity and elastic strain accumulation, calling for future investigations on their seismogenic potential.