Estimation of earthquake recurrence parameters for the Himalayan seismic belt: a comprehensive analysis

In this study, we conducted a comprehensive assessment of earthquake recurrence parameters along the Himalayan seismic belt (HSB), defined by coordinates 25°-35° N and 72°-98° E. Our analysis covered the estimation of critical earthquake hazard parameters, including Gutenberg-Richter (GR) parameters ‘b’ and ‘a’ values, mean seismic activity rate (λ), maximum regional magnitude (Mmax), return periods, and probabilities of distinct earthquake magnitudes. We utilized an extensive earthquake dataset spanning the period from 825 B.C. to 2023, which was categorized by depth into three ranges: shallow (h = 0–25 km), intermediate (h = 25–70 km), and deep (h ≥ 70 km). The dataset was homogenized based on moment magnitude (MW) and declustered to remove dependent events. Using the maximum likelihood technique, we estimated hazard parameters, integrating data from both historical and instrumental periods. The seismic source zones were classified into 34, 27, and 5 zones for depth intervals h = 0–25 km, h = 25–70 km, and h ≥ 70 km, respectively, based on seismic activity, focal mechanisms, and seismotectonic features. Geographical maps were generated for these zones at different depths to visualize variations in hazard parameters. Our findings highlighted significant differences in seismic hazard levels across the HSB, reflecting the complex crustal heterogeneities and tectonic intricacies of the region. Zones 16, 18, 26, 29, and 33 in the shallow depth range exhibited Mmax values of MW ≥8.0. In the intermediate depth range, zones 19, 22, and 24 showed potential for Mmax values in the range of MW 7.0-7.7. For the deep zones, zone 5 indicated a similar potential. The return periods for MW 7.0 earthquakes varied across the source zones and in the shallow depth range, it ranged from 35 to 94 years. For the intermediate depth range, return periods were between 329 and 789 years, and for the deepest zones, it ranged from 72.8 to 1300 years. Furthermore, the assessment of probabilities (> 0.70) has been performed for different zones across all depth ranges. This study underscores pronounced spatial disparities in seismic hazard levels along the Himalayan seismic belt, highlighting the need for detailed regional seismic hazard assessments to better understand and mitigate earthquake risks in this seismically active region.