Stochastic modelling of earthquake recurrence interval for North-East, India (Eastern-Himalayas) and its vicinity using Weibull, Gamma and Lognormal distribution

Abstract

Northeastern India is a tectonically complex and seismically active region that has experienced several damaging earthquakes. Statistical analysis of earthquake recurrence can provide supporting insights into regional seismic behaviour.Despite its seismic significance, time-dependent statistical characterization of earthquake recurrence in this region remains limited, particularly using established renewal models applied in a comparative framework. In this study, cumulative probabilities and conditional probabilities (hazard rates) were estimated for earthquakes with magnitudes Mw > 3.6, 4, 5, and 6 to examine which renewal model best describes earthquake recurrence in Northeastern India. Weibull, Gamma, and Lognormal distributions were applied to earthquake recurrence intervals. All three models provide a reasonable first-order description of recurrence behavior, with the Weibull distribution yielding a comparatively better statistical fit, followed by the Gamma distribution, while the Lognormal distribution shows weaker performance. Based on the Weibull model, characteristic recurrence intervals are estimated to be approximately 46, 58, 180, and 540 years for Mw > 3.6, 4, 5, and 6 earthquakes, respectively. Over a 70-year period, the estimated conditional probabilities increase within lower and upper time bounds for each magnitude class, indicating higher likelihoods with increasing elapsed time since the last event. In conclusion, the results suggest that renewal-based statistical models, particularly the Weibull distribution, can provide a preliminary characterization of earthquake recurrence behavior in Northeastern India, though the estimates are subject to the assumptions and limitations inherent in such models. The present study is intended as a preliminary investigation. Future work incorporating physically based models (e.g., Brownian Passage Time), higher magnitude thresholds, and more rigorous treatment of dependent seismicity is required to improve the robustness and hazard relevance of time-dependent seismic assessments in the region.