Fault population recognition through microseismicity in Mygdonia region (northern Greece)

Seismicity in the broader area of Mygdonia basin in northern Greece is lately characterized by the absence of strong events along active seismogenic faults known to have been activated in the past. Small to moderate magnitude earthquakes not exceeding ML4.8 have occurred in the last three decades. In this study, earthquakes occurred in 2000 and 2013 and recorded by the Hellenic Seismological network were investigated. Available Pand Sseismic wave arrivals were used for relocation in order to obtain accurately determined earthquake focal coordinates. For this scope, a Wadati diagram was constructed and a Vp/Vs ratio equal to 1.78 as well as time delays were included in the Hypoinverse process for the estimation of the focal coordinates. In the case of strong spatial or temporal clustering among earthquakes, the HypoDD algorithm was also employed for further improving location accuracy. The relocated seismicity was used in order to reveal the structural and geometrical properties of the local fault population and identify seismogenic faults deprived of a clear surface expression. For this reason, cross sections perpendicular to the main axis of the rupture zones were created, and finally a correlation between the kinematic properties and the current stress field was attempted. It is evident that in the absence of strong earthquakes, microseismicity is the only, however fundamental information to be exploited for the identification of active faults and the hazard assessment since small earthquakes are concentrated in areas with a significant potential for a future strong earthquake.