Seismic Hazard Analysis of Tunnel Structures-A Case Study

Abstract eng:
The Himalayan Orogenic belt constitutes the highest seismic hazard zone of the country and experiences moderate, large and great earthquakes since historical times with magnitude of the order of 8.5Mw. Immense developmental activities are taking place in the Himalayas by way of hydroelectric, communication, water supply and storage projects involving construction of tunnels and underground caverns. While, detailed seismic hazard assessment of the surface components of the projects are carried out, seismic vulnerability of underground structures like tunnels and underground caverns are generally not subject to rigorous analyses. The assessment of seismic vulnerability of the underground structures is of equal importance, particularly in higher seismic zones, and hence such studies are warranted. The present study, therefore, was undertaken to assess seismic hazard impacts of an underground tunnel structure in response to seismic activity as adumbrated by different methods. Data gathered for the last 500 years (both historical and instrumental data for the period available) revealed innumerable seismic incidences of magnitude ranging from 3.6 to 7.8 Mw between the years 1500 to 2012 in the Himalayas. This paper highlights the statistical seismology and its application in prognosticating a 7.0 Mw event within 100-year frequency which can lead to provision of corrective and control measures for one of the underground structure contemplated for communication.

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