No abstract

This paper describes a study carried out to analyse the historical records of earthquakes in the vicinity of Sri Lanka. The records indicate that the 1615 earthquake was the most significant earthquake that affected Sri Lanka. By analysing over 300 records of earthquakes around Sri Lanka, it was found that Mannar rift zone and Comorin ridge is the critical zone of influence which is capable of generating a seismic event of magnitude 6.9 at a 475 year return period at a depth of 10-15 km below the sea level. The study demonstrates that seismicity around Sri Lanka cannot be no longer ignored and engineering design should include seismic hazards.

Sri Lanka has been considered as a seismically safe country in the past considering the large distance from the island to active plate boundaries. However, with the increased degree of urbanization, the possible impact of intraplate earthquakes on population centres within the island has become important. In this context, deterministic and probabilistic seismic hazard assessments have been carried out by few researchers so far. However, these studies have not considered the influence of variation of bedrock profile on the seismic wave propagation. In the study presented here, a numerical simulation is carried out to investigate the effect of variation of the bedrock profile on the seismic wave propagation in Sri Lanka. The acceleration time histories of seven real time earthquake records, selected from the PEER database, were used as input in a numerical finite difference model simulating the two-dimensional bedrock response. The resultant spectra at the bedrock surface thus obtained are compared with those derived from the early studies. The comparison clearly shows the effect of ground elevation profile on seismic wave propagation, which should be taken into account especially when designing earthquake resistant structures in higher elevation areas.