Modeling Earthquake Recurrence in the Himalayan Seismic Belt Using Time-Dependent Stochastic Models: Implications for Future Seismic Hazards

Interest in and pertinent studies related to the seismic hazard in the Himalayan region have increased significantly since the instrumental era, and each damaging earthquake encourages its reestimation. In the work presented herein, the non-Poissonian probabilities of exceedance of magnitudes in a specified time in the future were investigated for different elapsed times based on the recurrence time intervals of past earthquakes in the Himalaya, using the Weibull, log-normal, gamma, and inverse Gaussian stochastic models. The whole Himalayan arc is divided into four seismogenic source zones, viz. the Northwestern Himalayas (zone 1), the Central Seismic Gap Region (zone 2), the Eastern Nepal and Sikkim (zone 3), and the Eastern Himalayas (zone 4), by considering approximately 380 years of seismological data. The suitability of each stochastic model for each zone was estimated using the Kolmogorov–Smirnov (K–S) test, to describe the different physical processes responsible for earthquake occurrence. The results show that the gamma, inverse Gaussian, log-normal, and inverse Gaussian models were most suitable for zones 1–4, respectively, for M ≥ 6.0. The cumulative probability of recurrence intervals reaches up to 90% in 30 years for zones 1 and 2, 49 years for zone 3, and 41 years for zone 4. The estimated conditional probability reaches 90% in 30 years in zone 1, 35 years in zone 2, and 50 years in zones 3 and 4. The most suitable models for M ≥ 7.0 were found to be the log-normal for zones 1, 2, and 3 and gamma for zone 4. The cumulative probability for M ≥ 7.0 reaches 90% in 85 years in zone 1, 86 years in zone 2, 93 years in zone 3, and 148 years in zone 4. The estimated conditional probabilities reach 90% in 80 years in zone 1, 90 years in both zone 2 and 3, and 150 years in zone 4. It is strongly recommended that model suitability be evaluated in complex regions such as the Himalaya before proceeding with seismic hazard assessments. The heterogeneous and complex tectonics of the Himalayas, differentiated plate motions, different stress release patterns (spatially and temporally), and locking/unlocking of faults/thrusts are some of the reasons responsible for the different probabilistic models describing the earthquake occurrence phenomena in these four zones.