Seismic quiescence of the seismicity associated with the Turkey earthquake occurred on 6 February 2023 using epidemic-type aftershock sequence (ETAS) model

Abstract

This study investigates the seismic activity during the Kahramanmaraş earthquake sequence that occurred on 6 February 2023 in Turkey. ETAS model has been adopted to analyse earthquake occurrence rates based on the transformed origin times and residual point process. The analysis reveals a period of approximately 5 years of reduced seismic activity preceding the earthquake sequence, indicating lower earthquake occurrence rates compared to the model’s predictions. In simpler terms, the study identifies a period of relative quiet seismic activity before the sequence, which can be attributed to the release of stress in asperity formations. Asperity formations arise from the collision of the Arabian and Eurasian plates, causing irregular stress accumulations along the Eastern Anatolian Fault Zone. Temporal distribution of b-values shows a statistical decline of seismicity, indicating increased stress in these existing asperities, characterized by localized mechanical coupling and material homogeneity around the areas where two major earthquakes occurred in February 2023. Particularly significant is the assessment of Coulomb stress change resulting from a magnitude, M_W 7.8 mainshock on the left-lateral strike Eastern Anatolian Fault Zone. This event leads to an increase in Coulomb stress change of 0.8–0.9 bar at the highly stressed Sürgü and Çardak faults. This heightened stress ultimately triggered a magnitude, M_W 7.5 earthquake, further contributing to the aftershock activity observed after the 2023 Kahramanmaraş earthquake sequence. In the light of these findings, this research suggests investigating periods of seismic quiescence or low b-values before earthquake sequences and quantifying positive stress changes afterwards. Therefore, the ultimate goal should be to reduce vulnerability, enhance resilience, and prevent the loss of life and property by these recurring disasters in the study region and in other parts of seismically active regions of the world. Hence, the risk management practices may be implemented in the seismic risk areas by the governments/policy makers and urban area planners.