A Macro Seismic Hazard Zonation for Sri Lanka

Abstract

This paper describes the outcome of a comprehensive study carried out to analyse the seismic hazards affecting Sri Lanka. The main seismic threat is from oceanic earthquakes originating at failed Mannar rift zone and Comorin ridge off the west to south west coast with some secondary influence from South Indian crustal earthquakes. The analyses were performed using Deterministic Seismic Hazard Assessment, Probabilistic Seismic Hazard Assessment and seismic wave propagation using FLAC software ignoring the overburden attenuation within the landmass. The seismic scenario included 100 years earthquake catalogue with an characteristic earthquake of magnitude 6.9 at a distance 90 km from the west coast. Historical records of earthquakes in the vicinity of Sri Lanka indicate that 1615 earthquake was the most significant earthquake that affected Sri Lanka. The analyses show that South West to North West coastal areas are the most vulnerable to seismic hazards. There is also reflection of seismic waves leading to amplification of seismic waves in the central highland. Based on the analyses described above, a seismic hazard map for Sri Lanka dividing the country into two zones of seismic intensity and response spectrum is provided accordingly. The study was constrained by the lack of recorded data of past earthquake responses within the country and a network of seismic stations are proposed in the paper for future data collection.