On 26th December 2004 off the coast of Northern Sumatra the fourth largest earthquake of this century occurred at 00:58 UTC. The quake occurred at a depth of 10 km, and was measured to 9.0 on the open ended Richter scale. A displacement of the tectonic plates will always generate a wave at the surface of the ocean - a so-called Tsunami.

In this case, the tectonic plates are estimated to have been displaced as much as 30 metres - thus, the energy released was equivalent to 10.000 Hiroshima atomic bombs.

As the Tsunamis travel across the open oceans, the amplitude of the wave of only a few centimetres is hardly noticeable. However, as they approach shore they will gradually build up and in areas where the topography of the seabed is especially suited they will reach heights of 10+ metres. Combined with the speed at which the Tsunamis travel of up to 800 km/h (500 mph) over the open ocean, slowing to 30-100 km/h as they reach shore, they can cause extensive damage as they have tragically done in the countries surrounding the Indian Ocean.

Tsunami simulations

At DHI we have attempted to simulate the phenomenon using our operational global 2D model (MIKE 21). A simulation has been run to illustrate this remarkable natural phenomenon. Because shoaling effects are what make the Tsunamis extreme, detailed information of the coastline is essential. With the flexible mesh version of the MIKE 21 model we are able to zoom in to a few locations where the Tsunamis have had the most devastating impacts. 

Preliminary model results

A coarse resolution model has been run immediately following the event with the information available at the time, and without the detailed coastal information. The results from this model illustrate how the Tsunami propagates across the Indian ocean and how it builds up on the coast, however the build-up is grossly underestimated in this set-up. The model is run without tide or wind, so it is the pure signal from the Tsunami.

An animation of the wave propagation across the Indian Ocean can be downloaded by clicking the image below (2.2 MB).  

Local effects 1

From the electronic navigational charts available for the area, more detailed topographies have been applied to the waters around Sri Lanka, the west coast of Thailand and Malaysia. Below are animations of the zoom-in on these areas. Yet the topography is too coarse to get the full devastating effect of the wave, it is evident how the effects can vary from one location to another depending on the local funnel effect of the bathymetry.

A zoom into one of the badly affected areas around Phuket, Thailand can be downloaded by clicking the image below: (2.2 MB)

A bit further into the Melaka Strait in Malaysia - can be downloaded by clicking the image below: (0.5 MB)

And finally around Sri Lanka: (0.8 MB) 

For an example of another Tsunami in the Atlantic follow this link:
A Tsunami in the Atlantic in 1755

Local effects 2

To illustrate how the height of a tsunami wave changes when it approaches the shore, a couple of simulations have been made with DHI's MIKE 21 model. This model includes the processes that determine how waves behave in coastal areas such as non-linear shoaling, diffraction, reflection, wave breaking and run-up. 

Simulation of propagation and transformation of a transient wave train as it hits the shore and proceeds further inland:(4,3 MB)

 As above in cross section view: (0,8 MB)  

Please Note: The 2D avi animations have been created using DivX compression.

You can download the DivX driver here.