Seismic quiescence and b-value anomalies preceding the 6th February 2023 earthquake doublet (MW 7.8, MW 7.6) in Kahramanmaraş, Türkiye: a comprehensive analysis of seismic parameters along the East Anatolian Fault Zone

Abstract

This study investigates seismic quiescence (Z-value) and b-value anomalies preceding the 6th February 2023 earthquake doublet in Kahramanmaraş, Türkiye (M_W 7.8, M_W 7.6), via compiled earthquake catalog from various sources, including Tan (Nat Hazard 21: 2059 2073,2021), KOERI, ISC, and USGS. We converted the catalog to both moment magnitude scale (M_W) and das magnitude scale (M_Wg) and conducted a comparative analysis—following which we adhered to the magnitude scale (M_W) for further study. Temporal completeness was assessed using the cumulative visual inspection method (CVI), while magnitude completeness was determined through the maximum curvature method (MAXC). The estimation of the b-value was carried out using the maximum likelihood method (MLM). Analyzing the spatial distribution of b-value revealed a low b-value region (b < 1) well before the events. Similarly, the temporal decline in the b-value curve was noted before the occurrence of the Türkiye earthquakes (M_W 7.8, M_W 7.6). Furthermore, the spatial distribution of the z-value indicated seismic quiescence, with the epicenters of the recent Kahramanmaraş, Türkiye, earthquakes (M_W 7.8, M_W 7.6) located in the positive z-value region which considerably aligned with the observed decrease in seismic activity from 2015 to 2023. Utilizing the Gumbel extreme value approach, we estimated seismic parameters, including maximum likelihood magnitudes, average recurrence intervals, and the probability of different magnitude occurrences for four sections of the East Anatolian Fault Zone (EAFZ): Amanos fault section, Pazarcık fault section, Erkenek fault section, and Çardak fault section. The study anticipates that the maximum annual earthquake magnitude for the Amanos fault segment exceeds that of the Pazarcık, Erkenek, and Çardak fault sections. Similarly, it expects the Amanos fault segment to experience major earthquakes (M_W ≥ 6.5) more frequently compared to the Pazarcık, Erkenek, and Çardak fault sections. Over the next century, the study projects a higher probability of major earthquakes for the Amanos fault segment compared to the Pazarcık, Erkenek, and Çardak fault segments. This study emphasizes the significance of these parameters in seismic hazard analysis, providing essential insights for evaluating seismic hazards in the East Anatolian fault region.