Evaluation of Tsunami Risk Posed to Sri Lanka by Potential Mega-Thrust Earthquakes in the Makran Subduction Zone

J J Wijetunge

doi:10.4038/engineer.v42i1.7066

Abstract

This paper is concerned with a numerical study carried out to assess the threat posed to Sri Lanka by potential tsunamigenic earthquakes in the Makran subduction zone in the Arabian Sea off the south coasts of Pakistan and Iran. The fault plane model adopted in the present simulations corresponds to a worst-case scenario of simultaneous rupture of the entire eastern segment of the Makran Trench. A hydrodynamic model based on linear shallow-water equations was employed to simulate tsunami propagation from the source to the shoreline around Sri Lanka. The numerical simulations suggest that the maximum nearshore tsunami amplitudes along the coastal belts of the Western, North-Western and Southern Provinces are of the order of 1 m; the corresponding values for the Eastern and Northern provinces are even smaller, about 0.2 m and 0.1 m, respectively. The model results also indicate that the tsunami waves will first hit the coastal belt of the Western Province about 280 minutes after the earthquake, followed by Southern and North-Western Provinces. The results presented in this paper would be useful for authorities responsible for evacuation to make a better judgement as to the level of threat in different areas along the coastline, and to act accordingly, if a large earthquake were to occur in the Makran subduction zone.

Highlights

The earthquake of moment magnitude Mro=9.19.3 [9] on 26 December 2004 in the AndamanSunda trench ruptured a 1200 km long segment, starting near the northern part of the Sumatra Island and ending offshore of the Andaman Islands
Besides the Andaman-Sunda Trench which produced the massive 2004 tsunami, the potential for occurrence of large tsunamigenic earthquakes that could affect Sri Lanka exists at two other subduction zones, namely, the Arakan Trench off Myanmar in the northern Bay of Bengal and the Makran Trench off Pakistan and Iran in the Arabian Sea [10] (See Fig. 1 for locations of these seismic zones)
In the farfield, the west coast of India, the Maidive Islands, and to a lesser degree, the west and south coasts of Sri Lanka are exposed to the tsunami wave front, besides the south coasts of Pakistan and Iran as well as Oman in the neighbourhood of the fault plane

Summary

Introduction

The earthquake of moment magnitude Mro=9.19.3 [9] on 26 December 2004 in the AndamanSunda trench ruptured a 1200 km long segment, starting near the northern part of the Sumatra Island and ending offshore of the Andaman Islands. As for the seismogenic potential of the fault line further north of Andaman Islands, Cummins [2] concluded that the Arakan Trench located off Myanmar is capable of generating a giant tsunamigenic earthquake with potential for causing great loss of lives and destruction His assessment was based on a detailed examination of the tectonic environment, stress and crustal strain observations as well as historical earth quake activity in the Arakan subduction zone. Wijetunge [20] examined the level of hazard posed to Sri Lanka by such a tsunami originating in the Arakan Trench by computing the likely maximum wave heights along the shoreline of the island His numerical simulations indicated that, in Sri Lanka, the Northern Province would be at a greator risk from a tsunami generated in the Arakan fault plane with maximum nearshore wave amplitudes on tire order of 10 m, whilst the. In this paper, a numerical model of tsunami propagation is employed to evaluate the level of risk to Sri Lanka from a tsunami generated by a potential mega-thrust earthquake in the Makran Trench

Tectonic Setting

Numerical M odelling

M odel Formulation

Results and Discussion

Conclusions