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Regional patterns of seismic b-values variations in the Himalayan region (71.6°E – 95.5°E and 37.5°N – 26.6°N)

Ram Krishna Tiwari1* ,  Anil Subedi1 ,  Dilip Parajuli1 ,  Santosh Dharel1 ,  Anil Neupane1 ,  Hari Subedi1 ,  Bishow Raj Timsina1 ,  Harihar Paudyal1
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1 Department of Physics, Birendra Multiple Campus, Tribhuvan University, Bharatpur, Chitwan, Nepal
JSE, 025210006
Submitted: 25 May 2025 | Revised: 5 July 2025 | Accepted: 8 July 2025 | Published: 28 July 2025
© 2025 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
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Abstract

This study conducts a detailed seismic hazard assessment of the Himalayan region. It focuses on studying how b-values, based on the Gutenberg–Richter law, vary throughout location and time. These fluctuations assist measuring tectonic stress and provide insights into the region’s seismic activity. This research focuses on five Himalayan sub-regions: Far Western, Western, Central-I, Central-II, and Eastern. It incorporates earthquake data spanning 1964 – 2023 obtained from the International Seismological Centre. The data were de-clustered using the Reasenberg method and examined by Maximum Likelihood Estimation. The results demonstrated considerable spatial variability in b-values across the Himalayan sub-regions. The Far Western Himalayas displayed the greatest b-value (0.93 ± 0.02), indicating frequent smaller earthquakes and lesser tectonic stress. In contrast, the Eastern (0.68 ± 0.02) and Central-I (0.69 ± 0.03) regions had the lowest b-values, implying more stress accumulation and a greater risk of future strong earthquakes. Temporal fluctuations, as a decrease in b-values preceding to the 2015 Gorkha earthquake (Mw 7.8) and a subsequent increase in Central-II (1.19 ± 0.03), highlighted the retention and release cycles. The Eastern Himalayas, particularly the Dhubri-Chungthang fault zone seismic gap in Bhutan, are considered a key high-risk zone. This region, with b-values ranging from 0.65 to 0.75, has remained unruptured since the 1934 Bihar-Nepal earthquake (Mw 8.4). The findings showed the influence of the continual convergence of the Indian and Eurasian plates (~20 mm/year) on strain heterogeneity. This study underlines the vital demand for intensive seismic monitoring, resilient infrastructure, and disaster readiness in low b-value areas to alleviate catastrophic risks in one of the globe’s most tectonically active regions.

Keywords
b-value
Gutenberg–Richter law
Himalayan region
Funding
None.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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