Another quake due

As we all know, Christmas is coming and who can forget the images from the Boxing Day tsunami that happened four years ago, and scientists this week have warned in the journal Science that the Indian Ocean could be due another major earthquake within the next couple of decades.

That's according to a team of researchers led by Kerry Sieh from the California Institute of Technology in the United States who have looked through a 700 year record of earthquake activity near West Sumatra.

To find this record they turned to the long stretch of coral reefs that fringe the Indonesian island along a zone known as the "Sunda Megathrust".

A bit like trees, reef-building corals also lay down annual growth rings. Coral reefs are built by millions of tiny creatures that look like miniature sea anemones living inside calcium carbonate egg cups. Over time corals build up layers and layers of carbonate forming huge reefs - and by drilling into the reef you can look at those growth rings and step back in time to unveil what was going on in the environment when the ancient corals were growing.

The link between earthquakes and corals is that when an earthquake pushes up the seafloor, causing a relative drop in sea level, it is likely to expose coral reefs so instead of growing upwards they grow outwards or they may stop growing altogether.

The clues left behind by the corals suggest that every two centuries for at least the last 700 years, there has been a sequence of multiple major earthquakes. So there was a series of big earthquakes in the 1300s, in late 16^th century, and from 1797 to 1833.

What should we expect to happen next? Back in September 2007 there was a moment magnitude 8.4 earthquake which researchers think could be the start of another of these major earthquake sequences.

What is extremely worrying is that 2 out of 3 of the past earthquake sequences began with smaller quakes before a really big one hit. And the 2007 quake was much smaller could occur based on the forces that will have built up since the last major event in 1833.

And it seems that the next major earthquake in this current sequence is due probably sometime in the next couple of decades - although it is very difficult to predict exactly when it will happen. But when it does arrive it would be likely to generate tsunamis that could be similar or even worse than the 2004 boxing day tsunami and that obviously is a great concern for people living in the area making it even more important that proper early warning systems and evacuation plans are put together for the region.