Spatial analysis of seismic parameters and their correlation with active faults in northwest Zagros

Abstract

The scientific basis for seismic risk assessment, safe engineering designs, and disaster risk reduction policymaking is the determination of seismicity parameters, and inaccuracy in these parameters can lead to overestimation or underestimation of risk. In Iran, which is a seismically active country, determining these parameters is essential. In this research, seismicity parameters in the northwest of the Zagros were first calculated for the entire region using three methods: CUVI, maximum curvature, and Kijko and Sellevoll (1992). Subsequently, their spatial variations were examined with a focus on the latter two methods within a geographic grid. The results indicated that the spatial distribution of seismic activity is strongly influenced by the location of the region’s major faults, including the Main Recent Fault, Mountain Front Flexural Fault, High Zagros Fault, and Zagros Front Fault. Seismic productivity (a-value) is significantly higher in areas near the Mountain Front Flexural Fault and the Zagros Front Fault, reaching over 3.8 in some central and western grids (maximum curvature method), while in sections farther from these faults and closer to the High Zagros Fault, this value sometimes drops to around 2.1. This pattern aligns with the number of complete earthquakes, identifying areas adjacent to the frontal faults as the most active zones. The b-value parameter also shows a close relationship with the type of faulting; very low values (less than 0.55) are mainly observed near the flexural and frontal faults, indicating a higher likelihood of large earthquakes in these mature compressive belts, whereas western areas influenced by secondary faulting and the Main Recent Fault exhibit higher b-values (around 0.85–0.90). These spatial heterogeneities, which are directly dependent on the position and behavior of the Zagros's major faults, highlight the need to revise uniform seismic hazard models. Zones with a combination of high a-value and low b-value along the frontal faults were identified as the highest-risk areas, requiring priority in GPS monitoring, paleoseismological studies, and immediate updates to probabilistic seismic hazard assessments (PSHA) for cities such as Kermanshah and its surroundings.