New constraints on extensional tectonics and seismic hazard in northern Attica, Greece: the case of the Milesi Fault

Northern Attica in Greece is characterized by a set of north dipping, subparallel normal faults. These faults were considered to have low tectonic activity, based on historical earthquake reports, instrumental seismicity, and slip rate estimates. This study presents new data for one of these faults, the Milesi Fault. We run GIS based geomorphological analyses on fault offset distribution, field mapping of post-glacial fault scarps, and ground penetrating radar profiling to image hanging-wall deformation. The first palaeoseismological trenching in this part of Greece allowed obtaining direct data on slip rates and palaeoearthquakes. The trenching revealed downthrown and buried palaeosols, which were dated by radiocarbon. The results of our investigations show that the slip rates are higher than previously thought and that at least four palaeoearthquakes with magnitudes of around M6.2 occurred during the last 4,000-6,000 years. We calculate an average recurrence interval of 1,000-1,500 years and a maximum throw rate of ~0.4-0.45 mm/a. Based on the new geological earthquake data we developed a seismic hazard scenario, which also incorporates geological site effects. Intensities up to IX must be expected for Northern Attica and the south- eastern part of Evia. Earthquake environmental effects like liquefaction and mass movements are also likely to occur. This scenario is in contrast to the official Greek seismic hazard zonation that is based on historical records and assigns different hazard zones for municipalities that will experience the same intensity by earthquakes on the Milesi Fault. We show that the seismic hazard is likely underestimated in our study area and emphasize the need to incorporate geological information in such assessments.This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/gji/ggv44