Assessment of Seismic Vulnerability of Structures in Sikkim, India, Based on Damage Observation during Two Recent Earthquakes

Recently, two earthquakes (MW=5.3 on February 14, 2006, and MW=6.9 on September 18, 2011) struck the mountainous region of Sikkim, one of the most seismically active regions in India. The 2006 event, though of lesser magnitude, clearly showed the high seismic vulnerability of different structures in Sikkim, especially in the state capital, Gangtok. Damage observed in buildings in and around Gangtok was disproportionately high during the 2006 event, considering the small size of the earthquake. It was expected and hoped that the 2006 event would act as a wake-up call to all stake holders in the society to improve the construction practices in the region. However, the bigger earthquake of 2011 not only affected the older structures but also severely damaged a large number of new structures. Comparison of observed damage with structures in Sikkim during these two earthquakes clearly demonstrates an alarming rise in seismic vulnerability of structures in Sikkim.