Preparing for the next tsunami
This article by Julian Hunt and first appeared on Reuters The Great Debate UK on Nov 3, 2010. Lord Hunt is a visiting professor at Delft University of Technology and emeritus professor at University College London, and former director-general of the UK Meteorological Office.
Dr Simon Day is a researcher at the Aon Benfield UCL Hazard Research Centre, University College London.
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. Following a magnitude 7.7 earthquake, 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 the 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 the recent disaster.
With Mentawai no more than 100 kilometres from the earthquake’s 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 percent 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.
Resilience also involves understanding how hazards affect local situations. Education for Self-Warning and Voluntary Evacuation (Eswave) is the best and most cost-effective method, whether in developed countries (as with earthquake drills in California) or in developing countries (as with tsunami-earthquake response procedures that saved many lives in Chile this year).
Eswave helps explain to local communities the diversity of tsunami waves (and the appropriate responses), such as:
● High surge waves, as occurred in Mentawai, which increase in height as they travel at speeds of about 10 metres a second or more up the beach and several kilometres inland, drowning and destroying villages in their path.
● Depression waves, as happened in Thailand and Sri Lanka in 2004 and in Samoa last year, when the water withdraws – lulling people into relaxing or even approaching the beach – before returning as large, surging waves.
The wider use of Eswave could have almost certainly saved lives in Mentawai by teaching local people to find higher ground or move further inland when they felt the initial seismic shaking or perhaps seen initial sea level changes. Survivor accounts indicate that they felt the earthquake, but that many did not react until the early tsunami waves were breaking on the shorelines.
This contrasts strikingly with the behaviour of many communities in the southwestern Pacific, who know that earthquake shaking often precedes a tsunami: mortality rates from tsunamis in such communities are at least 90 per cent lower than in adjacent communities of immigrants who are not tsunami-aware.
Forecasting is the second main way to mitigate tsunami risks. Perhaps the most promising research for improving our predictive skills is holistic geophysical forecasting.
This makes use of the fact that tsunami related disturbances are so large and so powerful that they disturb the solid earth, the oceans and the atmosphere. These disturbances do not lead just to mechanical forces and releases of heat, as in storms, but they also affect electrical, magnetic and molecular processes, especially higher up in the atmosphere.
Modern instruments have become so sensitive that they can measure magnetic fields one millionth of the strength of the earth’s magnetic field; they can detect tremors in the earth’s rigid outer layer long before large earthquakes and tsunamis actually occur. Research at Moscow’s Geoelectromagnetic Research Centre confirms that the motions in tsunami waves can be detected over many hundreds of kilometres from distant measurements of weak, slowly changing magnetic fields.
This new frontier of prediction is pathbreaking and already achieving exciting results. However, true success will only be achieved when human lives are routinely saved by applying both this and other tsunami-related research in practice.
