Delineation of relative tsunami risk for the coastlines of eastern and southern provinces of Sri Lanka

Abstract

This paper presents a preliminary assessment of the spatial distribution of tsunami risk for the Eastern and Southern Provinces of Sri Lanka. In the absence of probabilistic tsunami hazard assessments and detailed information on the vulnerability of coastal communities, field observations and numerical simulations of the 2004 tsunami were utilized to obtain the distribution of three parameters (the incident tsunami height, the horizontal inundation distance and the degree of damage to housing) that quantify the tsunami impact in the above two provinces. The incident tsunami height is reflective of the level of hazard, whereas both the inundation distance and damage to property partially reflect the vulnerability of each locality. Accordingly, in the present assessment, the distribution of relative tsunami risk is computed by factoring the influence of each of these parameters normalized with the respective mean value for the entire coastal sector. Two separate curves depicting the variation of the relative risk are compiled in this way for the Eastern and Southern Provinces. The results suggest that the several submarine canyons that are present in the eastern seaboard have a significant effect on the incident tsunami amplitudes, and consequently, on the risk distribution along the east coast. Moreover, the computed curve for the Southern Province indicates the influence of coastal geomorphology and onshore topography on tsunami risk. The high risk areas delineated in this study may be given priority in formulating mitigatory measures for tsunami threat.