The devastating tsunami that struck the Indonesian islands of Mentawai may have caused about 450 deaths, with hundreds more still missing, and compounds the disaster caused in the country by the eruption of Mount Merapi in Java on Tuesday. Following a magnitude 7.7 earthquake on Monday night, the Mentawai Islands were engulfed with estimated three-metre waves that affected thousands of households.
What has shocked many about this latest disaster is the fact that, more than five years after the cataclysmic Indian Ocean tsunami of 2004, when at least 187,000 people died (with 43,000 still missing), there were no greater preparations against last week's tsunami devastation. This is especially puzzling to some as, since 2004, our understanding of the risks of tsunamis and how to reduce their impact has advanced considerably through warnings, forecasting and better tsunami-resistant construction and design. For instance, in the past five years there has been significant progress in most aspects of warnings around the world, and the Indian Ocean region now has a system in place.
Much of the explanation for this apparent paradox stems from the fact that, even with a warning system in place, some communities close to epicentres may still not receive the warnings in time. This was exactly the issue with last week's disaster.
With Mentawai no more than 100 kilometres from Monday's earthquake epicentre, the tsunami waves reached the shores of the islands within 15-30 minutes; even if a tsunami alert had been issued by a warning system, it would have arrived too late for many people to have time to escape. This underlines the fact that, in almost all major earthquake-generated tsunamis (the exceptions occur when the source area is more or less uninhabited), at least 80 per cent of the casualties occur in the zone of felt seismic shaking from the source, and within the first hour.
So does this mean that there is nothing we can do to assist communities near earthquake epicentres from tsunamis? The short answer is 'no' in at least two main respects.
First, whether there are warnings or not, communities and infrastructure need to be resilient against the most likely kinds of natural hazards. Since 2004, for instance, many people near the Indian Ocean coastline sleep at higher elevations to avoid surprise tsunamis at night.
Research is now leading to more ambitious solutions for building resilient infrastructure. At several research institutes, including Delft University of Technology and University College London, laboratory wave-makers have reproduced tsunami events. But mathematical models and computations are now needed to turn the experiments into reliable estimates for engineers and for community planners to build tsunami-proof structures and plan more resilient communities. With global warming, these calculations also take account of the increasing danger as the sea level rises - which is happening three times faster in tropical seas where tsunami risk is greatest.