Seismic Risk Assessment in Hilly Areas: Case Study of Two Cities in Indian Himalayas

Past earthquakes in India and other countries have shown that hilly areas are subjected to higher losses as compared to the flat areas. This is due to combination of a number of factors, including topographic amplification, earthquake triggered ground failure hazard and higher vulnerability of hill buildings due to irregular structural configurations. This study identifies the role of these parameters through a case study of two cities in Indian Himalayas. An extensive field survey of the test-bed cities is conducted to identify different structural configurations prevalent in Indian Himalayas. Topographic amplification factors using three codes which deal with this issue, are compared and it is found that the Italian code (ICMS 2008) results in the most conservative amplification factors at the ridge. Seismic performance of the most commonly found hill building configuration is studied using Incremental dynamic analysis. The analysis shows that the hill buildings collapse at much lower PGA than their flat terrain counterparts, designed for the same hazard level, using Indian codes.