Geo- and seismo- tectonics of Eastern Himalaya: Exploring earthquake source zones from foredeep to Tibetan hinterland

Abstract

In this review we present our knowledge base on the seismicity and related tectonics of around 1200+ km stretch of the Eastern Himalaya from eastern Nepal to Arunachal Himalaya (AH) including southern Tibet hinterland in the north and frontal foredeep in the south. Succinct discussion on the India-southern Tibet convergence rate, geology and tectonic setup of eastern Himalaya, and variation in strain rate vis-a-vis location of large (Mw ≥ 7.0) earthquakes from the region is followed by analysis of five segments with unique seismotectonic characteristics from eastern Nepal to Mishmi region. Critical review leads us to reiterate the role of transverse structures across the Himalaya in shaping the seismotectonic response; the August 1988 eastern Nepal foothills and September 2011 Sikkim earthquakes are related to activity along transverse structures inherited from the Indian continental crust lithosphere, and thus arguably segmenting the Main Himalayan Thrust to restrict catastrophic rupture length for thrust earthquakes. The West-Central Bhutan lacks even normal level of seismicity compared to its immediate west (Sikkim-Darjeeling) and east (Eastern Bhutan-Western AH); this could be due to the fact that transverse seismogenic conjugate faults are also absent in this earthquake starved West-Central Bhutan. Alternatively, from the point of low strain rate scenario, this segment may be due for a bigger thrust event. The south Tibetan rifts are closely related to the Himalayan transverse faults and we suggest that the easternmost Cona-Oiga rift is possibly linked to the Western AH- Assam foredeep transverse Kopili- Bomdila trans-tensional faults.