An evaluation of tsunami hazard using Bayesian approach in the Indian Ocean

Abstract

The present study deals with the estimation of tsunami hazard parameters (maximum regional tsunami intensity Imax, slope β-value (where, β=b/log10e) of tsunami intensity–frequency relationship and tsunami activity rate λ) in the whole Indian Ocean as well as Andaman–Sumatra–Java (ASJ) region using Bayesian statistics technique. For this purpose a reliable, homogeneous and complete tsunami catalog during the period 1797 to 2006 with tsunami intensities (Soloviev–Imamura intensity scale) I≥2.0, having average wave heights H≥2.83m, is utilized. The slope (b-value) of linear tsunami intensity–frequency relationship (Log10N=a−b∗I) of G–R type for observed tsunami data with intensities I≥2.0 is calculated as 0.41. The applied method of Bayesian statistics follow three assumptions viz. Poissonian character of tsunami events, existence of the frequency–intensity relation of G–R type with a cut-off maximum value of tsunami intensities and catalog contains rather sizable events. In this study, the maximum regional tsunami intensity (Imax) has been estimated as 5.39±0.30 and 5.41±0.31 for the whole Indian Ocean and ASJ regions, respectively, which is reasonably comparable to the maximum observed tsunami intensity of 5.0 for August 27, 1883 Indonesia tsunami. The slope β-value of tsunami intensity–frequency relationship is calculated as 0.81 for both the Indian Ocean and ASJ regions by Bayesian statistics theory. We have also estimated quantiles of true and apparent tsunami intensities for future time intervals of 20, 30, 40 and 50years with confidence limits for probability levels of 50%, 60%, 70%, 80%, 90% and 95% in the Indian Ocean along with ASJ region. It is observed that the differences between true and apparent quantiles of tsunami intensities are negligible revealing that a good quality of tsunami data is used in the study. The results estimated in the present study have potential useful implications in the probabilistic tsunami hazard assessment in the Indian Ocean region.