Seismicity rate changes in association with the evolution of the stress field in northern Aegean Sea, Greece

Abstract

SUMMARY Seismicity rate changes in northern Aegean area were studied by applying the Dieterich (1994) Rate/State formulation. The study area was divided into four smaller ones that exhibit seismotectonic homogeneity and accommodate strong events with similar to identical focal mechanisms. Seismicity rate evaluation concerns the ‘study period’ between 1981 December 19 and 2010 August 31, whereas the reference seismicity rate was estimated for the ‘learning period’ lasting from 1970 January 1 to 1981 December 19. The coseismic slip of the strongest events (Mw≥ 5.8) that occurred during the study period was considered to contribute to the stress field evolution along with the continuous tectonic loading. Stress changes were calculated just before and after each strong event and their influence was then examined in connection with the occurrence rate of the smaller magnitude events above the individually determined magnitude of completeness in each subarea and for the respective time intervals. After defining the probability density function of seismicity distribution, a Rate/State model was used to combine static Coulomb stress changes (ΔCFF) with seismicity rates and to compare the observed with the expected rates of earthquake production for each time period and subarea. Different parameter values combinations were tested to evaluate the model sensitivity. Qualitative and quantitative correlations were performed for each one of the selected study periods. The modelling approach resulted to satisfactory correlation between real and synthetic seismicity rates and is expected to constitute a useful mean for the time-dependent seismic hazard assessment.