SEISMIC RISK ASSESSMNET DUE TO SCENARIO EARTHQUAKE: A CASE-STUDY FOR BIHAR-NEPAL EARTHQUAKE-I 934

Abstract

Bihar state sits on a high seismic zone which falls on the boundary of a convergent tectonic plate near the Bihar-Nepal border. Out of 38 districts in Bihar, 8 districts lie in Zone V. 24 districts in Zone IV and 6 districts in Zone Ill of the seismic zone. The Himalayan tectonic plate is moving towards the Indian Plate slowly and gradually. This dangerous plate tectonic behaviour has already caused a number of devastating earthquakes in the past. The continuous movement of plate projects an alarming picture for the state in future. The state has experienced high levels of destruction each time. The project focuses on the mitigation of the damage caused due to scenario earthquake in the state of Bihar. The Bihar-Nepal Earthquake-1934 has been taken as the scenario earthquake in this study. The term Scenario Earthquake' here refers to a condition in which a hypothetical recurrence of an earthquake is assumed in Bihar; whose magnitude, intensity and epicentre is considered same as of any previous earthquake of the focussed region of study. For the same reason, risk associated with the state has been identified by performing a Seismic Risk Assessment. Total expected direct and indirect losses are calculated in terms of rupees and number of deaths (caused due to the collapse of buildings) respectively. Consequently, the results obtained out of this assessment projects the most vulnerable districts of the state during any scenario earthquake. The project then discusses about the prevailing housing typologies in Bihar state. The most common type of building construction in the region, i.e. Burnt Brick Construction; has been identified and discussed in context of the state. Since, Bihar has witnessed a number of earthquakes in the past; buildings of the state have suffered great damage. In this context, the building deficiencies and damage trend observed in such structures have been laid out. Further, based on scenario studies, the first eight worst affected districts of the state have been projected. The typical types of cracks and building failures observed in burnt brick masonry structure due to the previous earthquakes are also outlined. Eventually, retrofitting recommendations for this typical construction has been given.