Ten years after the Boxing Day tsunami, are coasts any safer?
How do tsunami warning systems work?
All warning systems work in the same general way. First, a network of broadband seismometers detects the seismic waves generated by an earthquake, which travel at speeds of several kilometers per second. When several seismometers have detected the seismic waves, the location and approximate magnitude of the earthquake can be computed. If the epicenter is under water and the magnitude large (greater than 6.5 on the Richter, or moment magnitude, scale) a tsunami bulletin, watch or warning is issued to local communication centers, ideally within three minutes of the earthquake. If the epicenter is nearby and the probability of a tsunami is high, evacuation procedures will be initiated immediately.
Otherwise, local centers will standby for confirmation of whether a tsunami has actually been generated. Confirmation comes within about 30-60 minutes, using a network of tsunami buoys and seafloor pressure recorders. These detect the series of waves (usually less than a couple of meters high and travelling at about 800 km/h) in the open ocean, and transmit the data by satellite to a regional control center.
Tsunami warnings reach the public via TV, radio, email, text messages, sirens and loudspeakers. You can sign up to receive tsunami alerts anywhere in the world by SMS on your mobile phone, thanks to a not-for-profit humanitarian service called CWarn.org.
Many high-risk areas also have signage to alert people to “natural” warnings (such as strong shaking or a sudden withdrawal of the sea), and direct them to higher ground.
Limitations of warning systems
The Pacific and Japanese warning systems helped to ensure the major tsunami generated off the coast of Japan on 11 March 2011 caused far fewer deaths(15,000) than the 2004 disaster. However, it showed that even a wealthy and well-prepared nation such as Japan cannot fully protect people from extreme hazards, and that warning systems can sometimes lead to a false sense of security.
The slow rupture of the subduction zone near Japan meant the initial warnings underestimated the magnitude of the earthquake and resulting tsunami. Many people did not move to higher ground in the vital few minutes after receiving the warning, because they wrongly assumed the tsunami would be stopped by 5-10 m high sea walls.
Japan has learned from this tragedy and, among other things, made changes to tsunami warning messages, improved coastal defenses, and installed more seismometers and tsunami buoys.
Will more tsunami disasters occur?
It is impossible to predict exactly when or where the next major tsunami will occur. They are very rare events in our limited historical record. But by dating prehistoric tsunami deposits, we can see that major tsunamis happen on average every few hundred years in many coastal regions.
Future tsunami disasters are inevitable, but with better technology, education and governance we can realistically hope that a loss of life on the scale of the 2004 tsunami disaster will not happen again.
Emily Heath is Senior Teaching Associate, Lancaster Environment Centre at Lancaster University. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).
