Spatial variability of earthquake hazard parameters, return periods and probabilities of earthquake occurrences in the eastern Himalayan seismic belt

Abstract

We present a brief atlas of the geographical distribution of earthquake hazard parameters, return periods and probabilities of exceedance of medium to large earthquakes in a hazardous region of the eastern Himalayan seismic belt. A maximum likelihood procedure is applied for the purpose that allows earthquake data during 1500–2019 containing the mixed files of both the historical as well as instrumental era. The results reveal a high activity rate (λ) in eastern Nepal and Arunachal Himalaya, and a low value in the Bhutan-middle Arunachal-Assam Himalaya. A high b-value (or β-value) associated with eastern Nepal and its vicinity, Shillong Plateau and eastern Arunachal Himalaya reveals low crustal stress, while a low b-value associated with Bhutan, middle Arunachal, western Assam and east of the Lhasa reveals high differential crustal stress. The high values of Mmax (Mw > 8.0) are perceived in eastern Nepal, eastern Arunachal Himalaya, Shillong Plateau and south of Lhasa in Tibet. The return periods and probability of exceedance for magnitude Mw 6.0, 6.5 and 7.0 during the next 10-, 20- and 50-years are calculated and correlated with the prevailing tectonics and seismicity of the area. The low return periods (10–20 years) and high probabilities (>0.8) for magnitudes Mw 6.0–6.5 are associated with eastern Nepal, Shillong-Kopli Fault-Arunachal Himalaya, Eastern Himalayan Syntaxis and Yadong-Gulu rift in Tibet revealing potential regions for future earthquake hazard. These hazard maps are highly useful to prepare earthquake hazard mitigation plan in high hazard regions.