Comparison of ETAS parameter estimates across different time windows within the North and East Anatolian Fault Zones, Turkey

Abstract

Located at the intersection of major lithospheric plates, Turkey is characterized by significant seismic activity, particularly along the North Anatolian Fault (NAF) and East Anatolian Fault (EAF). This paper employs the Epidemic-Type Aftershock Sequence (ETAS) model, fitted using the BFGS quasi-Newton method, to study earthquake triggering processes along these faults from 1990 to 2023. Our findings show distinct temporal variations in seismicity parameters along these faults. Along the NAF, the ETAS model highlighted a lower background seismicity rate ($\mu$) and aftershock productivity ($K_0$) compared to the EAF. In contrast, the EAF exhibits lower magnitude sensitivity ($\alpha$), indicating that smaller earthquakes are more likely to trigger aftershocks, due to weaker dependence on mainshock magnitude. The aftershock decay rate ($p$) is notably faster in the NAF, suggesting quicker post-event stabilization. Our analysis across different time windows reveals significant non-stationarities in ETAS parameters, indicating that seismic behaviors along these faults do not strictly follow historical patterns. This temporal variability highlights the challenges in short-term seismic forecasting using historical data alone. A detailed comparison of ETAS parameters across time frames showcases the necessity for incorporating dynamic modeling approaches to improve earthquake forecasting in seismically active regions.