Stela Simeonova

Strong earthquake with moment magnitude MW7.5 hit the city of İzmit, Turkey with devastating effect in August 1999. The earthquake occurred in the North Anatolian Fault (NAF),and was followed by an intensive aftershock activity. It is assumed that the studied earthquake is a part of a seismic sequence that started in 1939 along the North Anatolian Fault. Over a period of 60 years or more, a series of large earthquakes moved progressively from east to west by the fault. The analysis of the space-temporal pattern of seismic clusters (foreshocks and aftershocks) distribution of the 1999 Turkey earthquake, is presented in the research. The properties of aftershock sequence (distinct cluster in space and time) allow for a time-dependent prediction of aftershock probabilities. Aftershock activity can sometimes cause more destruction than the main earthquake, due to factors such as radiation pattern, location and the cumulative nature of building damage. If the distribution of aftershocks over time is considered as a non-stationary Poisson process, the maximum likelihood method is used to estimate the parameters of the modified formula of Omori - power-low decay. A transformation from the time scale t to a frequency-linearized time scale τ is applied to test the correspondence between different statistical models and the occurrence of an aftershock sequence. As a final step of the study, a criterion - Akaike’s information criterion is used to determine the best model for the temporal distribution of aftershocks. The results of the study show that the precursor aseismic gap before the August 1999 MW7.5, Turkey earthquake is not observed. The aftershock sequence shows a complex temporal pattern - one secondary aftershock sequence with a different value of p – parameter.