In contrast to the almost complete absence of earthquakes in the interior of the Indian Plate, seismicity surrounds its edges and is prolific within the Tibetan Plateau. Most of the earthquakes within the Himalaya occur at shallow depth (<30 km); with deep earthquakes indicating the descent of the Indian Plate into the mantle at the ends of the arc. Earthquakes with depths exceeding 40 km are relatively rare in the continent–continent collision in the central Himalaya and beneath Tibet, indicating the absence of the Benioff–Wadati zone that is characteristic of oceanic plate collisions.
he rate of convergence between the Indian Plate south of the Himalayan foothills and southern Tibet is important because it provides an upper limit for the anticipated rate of seismic productivity for the Himalaya. With an average rate of convergence of 17 mm a?1, the 2000 km-long approximately100 km-wide Main Himalayan Thrust (the décollement separating the Indian and Asian plates) accumulates seismic moment at a rate of c. 1020 N m a?1 (Newton metres per year), equivalent to that released by a Mw = 7.3 earthquake. In 10 years, enough moment has accumulated to drive a Mw = 8 earthquake, and in a century a Mw = 8.6 earthquake. In just 350 years, were no other earthquakes to occur in the Himalaya, a Mw = 9 earthquake would be needed to release the accumulated 4 m of Himalayan convergence (assuming a 2000 km-long rupture).