Spatio-temporal variations of seismicity parameters before and after the 2023 Kahramanmaraş earthquake, Türkiye

In this paper, the spatial and temporal variations in seismicity parameters before and after Mw 7.8 and Mw 7.7 on February 6th, 2023, in the Kahramanmaraş region with 45,568 events recorded by the AFAD network have been investigated. After the declustering technique based on the Urhammer method (1986), a background catalog of 17,342 independent earthquakes was obtained. This enables an assessment of long-term tectonic behavior. From the magnitude-depth distribution, it is evident that most of the seismicity is shallow and restricted to the upper crust. Temporal changes in magnitude completeness show stable long-term behavior, apart from a temporary increase in 2023 due to network saturation from the intense aftershock sequence. From the frequency-magnitude analysis, a low b-value of about 0.83 indicates high levels of differential stress and a mechanically coherent fault system. This is consistent with high levels of seismic productivity. From the spatial analysis of b-value and Z-value, it is evident that both parameters clearly show changes before and after the earthquake. Before the mainshock, a significant decrease in b-value and Z-value indicates a zone of stress accumulation and seismic quiescence. This zone corresponds to the area of the mainshock. After the mainshock, an increase in b-value and Z-value indicates stress release and microfracturing. From the analysis of seismicity parameters before and after the earthquake, it is evident that high-quality analysis of seismicity provides useful insights for seismic hazard assessment.