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Contrary to most of the earlier theories that great earthquakes (M w 8.5 or even larger) may occur anywhere along the Indian plate boundary assuming uniform strain accumulation, this paper proposes two types of gaps with discriminatory characteristics. The new gaps were initially identified from earthquakes of magnitude 6, whose return periods in Himalaya vary between 20 and 30 years and are well within the period of reliable instrumental data of about 100 years. These gaps were then integrated with the largest magnitude event in instrumental era and historical times; information on paleoseismicity, micro-seismicity data, GPS-based geodetic observations and the tectonic features. The regions where great/major earthquakes (Mw 8 or larger) have occurred in the past are classified as seismic gap of category 1, namely Kashmir, west Himachal Pradesh (Kangra), Uttarakhand to Dharachulla, central Nepal to Bihar, Shillong, Arunachal gap including Assam-Tibet-Myanmar syntaxis. On the other hand, the second category of seismic gap includes JammuKishtwar block, east Himachal Pradesh, western Nepal (excluding Dharachulla region) and Sikkim-Bhutan where history of large earthquakes is not available. In these gaps, the largest earthquake magnitude is smaller (7-7.5) and the recurrence interval for earthquakes of same magnitude is larger as compared to category 1 gaps.

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