Janaka J. Wijetunge

Assessment of potential tsunamigenic seismic hazard to Sri Lanka

Purpose – The purpose of this paper is to present an assessment of the potential tsunamigenic seismic hazard to Sri Lanka from all active subduction zones in the Indian Ocean Basin.Design/methodology/approach – The assessment was based on previous studies as well as past seismicity of the subducion zones concerned.Findings – Accordingly, four seismic zones capable of generating teletsunamis that could reach Sri Lanka have been identified, namely, Northern Andaman‐Myanmar, Northern Sumatra‐Andaman and Southern Sumatra in the Sunda trench and Makran in the Northern Arabian Sea. Moreover, plausible worst‐case earthquake scenarios and respective fault parameters for each of these seismic zones have been recommended.Research limitations/implications – However, other potential tsunami sources such as seismic activity in the near‐field, submarine landslides and volcanic eruptions have not been considered.Practical implications – Numerical simulations of tsunami propagation have been carried out for each of the f...

VELOCITY AND TURBULENCE DISTRIBUTION IN COMBINED OSCILLATORY AND STEADY FLOW BOUNDARY LAYER OVER A RIPPLED BED

This paper describes an experimental study carried out in a laboratory water tunnel to examine the mean, periodic and turbulent components of the velocities in combined oscillatory and steady flow boundary layer over a fixed bed of vortex ripples. The fluid velocities, both the horizontal and the vertical components, were measured simultaneously with a laser Doppler anemometer. The measurements indicate that the addition of a steady current causes a significant effect on the near-bed ensemble velocity field of the oscillatory motion, owing primarily to the asymmetry of the lee-vortices that are formed during each half cycle of the oscillation. On the other hand, the effect of adding an oscillatory motion on the time-mean velocity field of a steady current is also significant in that the current experiences a considerably enhanced roughness due to the additional turbulence produced by the wave motion. The measurements also indicate that, depending on the spatial position over a ripple wave length, the turbulent intensities in combined flows are either increased or decreased with respect to the same in oscillatory flow alone. However, peak values of the spatially averaged turbulence quantities in the near-bed interaction layer of combined flows do not show a significant change with respect to the pure oscillatory flow components. The decay of turbulence as well as the near-bed momentum transfer in combined flows have also been examined.

Indian Ocean Tsunami on 26 December 2004: Numerical Modelling of Inundation in the City of Matara on the South Coast of Sri Lanka

On December 26, 2004, the coastal belt of Sri Lanka as well as several other countries bordering the Indian Ocean suffered massive loss of life and damage to property due to the tsunami unleashed by the third largest earthquake ever recorded. One way of mitigating potential loss of lives from a similar event in the future is through advance warning of impending tsunami and quick evacuation of vulnerable coastal communities to safer areas. The detailed planning required for such evacuation exercises is usually carried out based on tsunami inundation maps. Accordingly, the present paper outlines the numerical modelling carried out to develop a high-resolution tsunami inundation map, as a case study, for the city of Matara on the south coast of Sri Lanka, which was devastated by the 2004 tsunami. The results give the spatial distribution of the extent of inundation as well as the maximum flow velocities due to an event similar to the 2004 tsunami.