Seismic Behavior of Historic Masonry Monasteries in Sikkim in the 2011 M 6.9 Sikkim Earthquake: Case Study of Hee Gyathang Monastery, North Sikkim, India

Abstract

The Himalayan region is, one of the most seismically vulnerable and tectonically active zones in the world. Sikkim is a state in North-East India, situated on the Himalayan arc. Sikkim is dotted with numerous Buddhist monasteries dating back to the 17th century. These historical monastery structures are a part of the rich cultural heritage of the state, being structures of social, cultural and religious significance to the community. The old monasteries are typically load bearing structures where stone masonry and timber are used extensively as columns, beams, floors, roofs and also in staircases. The monasteries follow some spatial characteristics such as regular geometrical shapes in plan with an assembly hall and front verandah, and are usually one or two storeys high with diminishing upper storeys topped by light weight sloped roofs. The M6.9 earthquake on September 18, 2011, in Sikkim has clearly demonstrated the vulnerability of the historical monastery structures. The evaluation of the earthquake vulnerability of monasteries is a necessary first step for their protection in future earthquakes. This paper analyzes the performance of one of the non-engineered monastery structure made with load bearing stone masonry - the century old hilltop Hee Gyathang Monastery located in the North District about 30 kms from Mangan. Structural analysis by demand capacity method of this monastery proves that the monastery is unsafe after the 2011 M 6.9 Sikkim Earthquake.