Professor Kerry Sieh is a geologist at the California Institute of Technology. In 2004, Sieh’s team had been anticipating that a devastating Indian Ocean tsunami was likely to happen sometime soon, triggered by a shift at the Australian-Eurasian plate boundary. Less than two weeks before the Boxing Day tsunami, at a conference of the American Geophysical Union, Professor Sieh warned of an impending Sumatran earthquake.

The plate boundary near Sumatra is a subduction zone – a region where one plate sinks beneath the other. Where the two plates slide past one another the movement is not smooth but the two plates 'catch' and lock together, building up stresses. When the plates suddenly slip, as they did on 26 December 2004, the liberated energy causes an earthquake.

In tropical oceans, large earthquakes cause coral reefs to rise or sink. This kills the corals, if they rise above the sea surface, or stunts their growth, if they sink. Professor Sieh and his team, by sawing through coral clumps, could reveal the coral growth record rather like the rings of a tree. Doing so, they can decipher the pattern of earthquakes over centuries.

On average, major earthquakes happen in the Sumatra region every 200-230 years or so. The last two major episodes were in 1797 and 1833. So in 2004 Professor Sieh was expecting one to happen soon. And geophysical measurements showed that stresses were building up in Sumatra’s nearby subduction zone. So concerned was Professor Sieh about the potential tsunami hazard that he toured Indonesia trying to convince officials to take the tsunami danger seriously. He finally resorted to distributing tsunami advice posters in Sumatra, an action that saved hundreds of lives.