Gujarat and adjacent regions, located along the western margin of the Indian plate, are among the most seismotectonically active areas in the Indian Peninsula and have experienced significant seismic events such as the 1819 Allah Bund (MW 7.8) and the 2001 Kachchh (MW 7.6) earthquakes. This study employed a maximum likelihood approach to quantitatively assess key earthquake hazard parameters in 15 identified seismogenic source zones. The targeted parameters are the maximum possible magnitude (mmax), seismic activity rate (λ), Gutenberg-Richter b-value, earthquake return periods, and probabilities of future seismic events. A unified, Poissonian and complete earthquake catalogue was compiled to facilitate this analysis from 1819 to 2021, with a magnitude range of MW 2.0–7.8. The estimated maximum magnitudes (mmax) exhibited a range of MW 4.61–8.25, with the lowest occurring in Zone 6 (northern Cambay rift) and the highest in Zone 1 (Allah Bund). The b-value range was found equal to 0.47–0.88, with the minimum value in Zone 7 (northern Mainland) and the maximum in Zone 3 (Gedi Fault) revealing a pronounced differential crustal stress regime. The range for the seismic activity rate (λ) for a threshold magnitude of MW 3.6 was between 0.03 and 0.60 events per year, with the lowest rate in Zone 2 (northern Kachchh) and the highest in Zone 4 (the 2001 Kachchh earthquake). The shortest return periods are observed in zone 4 (e.g., 7.5 years for MW 5.5 and 60 years for MW 7.0) for a particular threshold magnitude, indicating a heightened frequency of substantial seismic events in this zone relative to that of other zones. The occurrence probabilities for different magnitudes over the next 20, 50, and 100 years indicate the highest likelihoods in Zone 4, with a 56% probability for a MW 7.0 event within 50 years and 80% within 100 years. The combination of low return periods (< 50 years) and high probabilities of occurrence (> 75%) specified Zones 1 (Allah Bund), 4 (2001 Bhuj earthquake), and 12 (Rajkot-Paliyad) as the most hazardous areas in the study region. The spatial variability of the estimated earthquake hazard parameters elucidates the heterogeneous seismic hazard levels across various zones, providing essential insights for future seismic hazard assessments and developing risk mitigation strategies.

Estimation of earthquake recurrence parameters for a delimited seismic source model in Gujarat and the adjacent region of the Western Indian plate margin

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2025年7月29日

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P. Chauhan,
R. B. S. Yadav,
A. Kijko

摘要

Gujarat and adjacent regions, located along the western margin of the Indian plate, are among the most seismotectonically active areas in the Indian Peninsula and have experienced significant seismic events such as the 1819 Allah Bund (M_W 7.8) and the 2001 Kachchh (M_W 7.6) earthquakes. This study employed a maximum likelihood approach to quantitatively assess key earthquake hazard parameters in 15 identified seismogenic source zones. The targeted parameters are the maximum possible magnitude (m_max), seismic activity rate (λ), Gutenberg-Richter b-value, earthquake return periods, and probabilities of future seismic events. A unified, Poissonian and complete earthquake catalogue was compiled to facilitate this analysis from 1819 to 2021, with a magnitude range of M_W 2.0–7.8. The estimated maximum magnitudes (m_max) exhibited a range of M_W 4.61–8.25, with the lowest occurring in Zone 6 (northern Cambay rift) and the highest in Zone 1 (Allah Bund). The b-value range was found equal to 0.47–0.88, with the minimum value in Zone 7 (northern Mainland) and the maximum in Zone 3 (Gedi Fault) revealing a pronounced differential crustal stress regime. The range for the seismic activity rate (λ) for a threshold magnitude of M_W 3.6 was between 0.03 and 0.60 events per year, with the lowest rate in Zone 2 (northern Kachchh) and the highest in Zone 4 (the 2001 Kachchh earthquake). The shortest return periods are observed in zone 4 (e.g., 7.5 years for M_W 5.5 and 60 years for M_W 7.0) for a particular threshold magnitude, indicating a heightened frequency of substantial seismic events in this zone relative to that of other zones. The occurrence probabilities for different magnitudes over the next 20, 50, and 100 years indicate the highest likelihoods in Zone 4, with a 56% probability for a M_W 7.0 event within 50 years and 80% within 100 years. The combination of low return periods (< 50 years) and high probabilities of occurrence (> 75%) specified Zones 1 (Allah Bund), 4 (2001 Bhuj earthquake), and 12 (Rajkot-Paliyad) as the most hazardous areas in the study region. The spatial variability of the estimated earthquake hazard parameters elucidates the heterogeneous seismic hazard levels across various zones, providing essential insights for future seismic hazard assessments and developing risk mitigation strategies.