March 23, 2010

Tsunami Generator Will Help Protect Against Future Catastrophe

A unique wave-generating machine that mimics the activity of real-life tsunamis with unprecedented realism has been used successfully in an Oxfordshire laboratory.

The simulator has copied the behavior of the first massive wave of the 2004 Boxing Day tsunami.

Developed and built with Engineering and Physical Sciences Research Council (EPSRC) funding, the tsunami generator will improve understanding of how tsunamis behave.

This will aid development of more effective evacuation guidelines for parts of the world potentially at risk from future tsunamis. It will also help improve the design of buildings in susceptible areas so they are better able to withstand the impact of such events.

The innovative new facility has been developed jointly by EPICENTRE (the Earthquake and People Interaction Centre), based at University College London, (UCL) and consulting engineers HR Wallingford, at whose headquarters it is located.

Mounted in a 45 meter-long wave channel, the tsunami generator uses a pneumatic (i.e. air-driven) system comprising a fan and control valves to suck up water into a tank and then release it in a controlled way. This makes the facility fundamentally different from all other wave simulators worldwide, which generally use pistons to produce waves by pushing at the water.

The new pneumatic technique has a range of advantages over a piston-based approach. In particular, tests by UCL researchers at HR Wallingford have shown that it can reproduce the draw-down phenomenon that is characteristic of 'trough-led' tsunamis where the sea is sucked out first before rushing back towards the shoreline.*

Within the wave channel, or 'flume', the waves created by the tsunami generator are directed over a model coastal slope, enabling their behavior and effects to be studied in detail.

Specifically, tests with this facility will be used to enhance understanding of the water flows and forces unleashed by tsunamis. This will enable buildings and infrastructure in vulnerable parts of the world to be designed and built in ways that help them withstand these destructive events.

Moreover, because this understanding will make it easier to predict the behavior of tsunamis at shorelines and when they move inland, the tsunami generator will make it possible to strengthen emergency and contingency planning at regional, national and individual community level.

"Although the basic concept is actually quite simple, this is the only facility that has ever been able to replicate the draw-down phenomenon in the laboratory", says Dr Tiziana Rossetto, EPICENTRE's Director. "We've already used the generator to mimic the 2004 Indian Ocean tsunami at 1:75scale. The data gathered should be validated and then made available to the scientific community within the next two years."

The tsunami generator was designed, built and tested between 2007 and 2009. EPSRC support was supplemented by additional funding from HR Wallingford and a studentship supported by consulting engineers Arup.

The aim is to make the tsunami generator available for use by other researchers from all over the world.

* When an earthquake fault displaces the overlying water and causes a tsunami, waves propagate outwards from the source. Because one of the oceanic plates involved in the earthquake moves upwards and the other moves downwards, these waves are led by crests on one side of the fault and by troughs on the other. For example, in the 2004 Boxing Day tsunami in the Indian Ocean, Thailand was hit by a 'trough-led' wave whilst Sri Lanka was hit by a 'crest-led' wave.

The tsunami generator can also create longer-wavelength waves than conventional, piston-based wave generators, making the waves much more like real tsunamis. Piston-based wave generators do not have the length of stroke needed to reproduce the entire wavelength of a tsunami, even at laboratory scale. Tsunamis can have wavelengths of several hundred kilometers in the open ocean.

Tsunami waves can cause extensive loss of both life and infrastructure. Generated by earthquakes, underwater landslides, volcanic eruptions or major debris slides, tsunamis travel across seas and oceans with quite small vertical displacements, but then shoal up dramatically in coastal and nearshore depths.

The tsunami triggered by the 8.8 magnitude earthquake off the coast of Chile on 27 February 2010 led to tsunami warnings being issued across the Asia-Pacific region. In Chile itself, waves over 2.5 meters high were reported, causing a number of deaths and substantial damage to infrastructure and property. On the Chilean side, the tsunami was crest-led, whereas towards Hawaii, for instance, there was a small trough before the crest.

The 2004 Boxing Day tsunami in the Indian Ocean was triggered by an undersea earthquake off the coast of Sumatra in Indonesia. This tsunami actually consisted of three to four successive wave peaks in total. It is estimated that nearly a quarter of a million people lost their lives in the tragedy.


Image 2: Tsunami Generator before being lowered into the flume. The baffles (the horizontal blue bars) stop sloshing inside the tank which gives better control of the generation of the wave.

Image 3: The 2004 Boxing Day tsunami in Thailand


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