Temporal, Spatial, and Depth-Dependent Seismicity of Takhar, Afghanistan: Insights from b-Value Variations and Seismic Moment Release

Understanding the temporal, spatial, and depth-dependent characteristics of seismicity is essential for evaluating earthquake processes and seismic hazard in tectonically complex regions. This study investigates the seismicity of Takhar Province and its surrounding region, Afghanistan, using a catalogue of 5,076 earthquakes recorded between 1926 and 2025. The earthquake catalogue was processed by removing duplicate and incomplete records and homogenizing magnitude information to moment magnitude (Mw). The Gutenberg–Richter relationship was applied to characterize earthquake-size distributions and variations in the b-value across temporal, spatial, and depth domains. The overall b-value was estimated at 1.18 ± 0.02, with a magnitude of completeness (Mc) of approximately 4.6. Spatial analysis revealed substantial heterogeneity, with b-values ranging from approximately 0.8 to 2.2 and relatively low values concentrated in several parts of Takhar. Temporal analysis showed a distinctly non-uniform pattern, characterized by relatively quiet intervals interrupted by episodes of enhanced seismic activity. Temporal b-values also varied among major seismic sequences. Cumulative seismic moment revealed abrupt increases associated with major earthquakes, reflecting episodes of rapid seismic moment release. Depth-dependent variations in b-value demonstrated significant vertical heterogeneity in seismic deformation. Overall, the results indicate that Takhar exhibits a complex and heterogeneous seismic regime across time, space, and depth within the broader Hindu Kush–Pamir tectonic system. The findings provide useful statistical constraints for understanding earthquake-generating processes and improving regional seismic-hazard assessment.