Chris Smith: Helen, this sounds rather scary. The coral clock says that we might be overdue for another tsunami.
Helen Scales: Yes, 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. Now 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.
Now to find this record they turned to the long stretch of coral reefs that fringe the Indonesian Island along a zone called the Sunda Megathrust. Now a bit like trees, reef building corals also lay down annual growth rings, and 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 these ancient corals were growing.
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Chris Smith: So how would we know when a tsunami had happened from that coral clock?
Helen Scales: Well, the link between the earthquakes and the corals is that when the earthquake pushes up the sea floor, and causing a relative drop in sea level, it’s likely to actually expose coral reefs. So instead of growing upwards they actually grow outwards, or they might even stop growing altogether, and of course it’s the earthquakes we know that cause the tsunamis. So the clues left behind by these corals suggest that every two centuries, for at least the past 700 years, there's been a sequence of multiple major earthquakes.
Chris Smith: So what's the chances of history repeating itself?
Helen Scales: Well, what we see is back last year in September 2007 there was a moment magnitude 8.4 earthquake, and researchers think this could be the start of another one of these major earthquake sequences, and what's particularly worrying is that two out of those three past earthquake sequences began with smaller quakes which hit before a really big one arrived. And this 2007 quake was actually much smaller than it could have been if we think about how much the forces have built up during the time that's passed since that last major event in 1833.
So the chances are a big one is coming along. We don’t quite know when it’s going to be. But, when it does arrive, the chances are it will generate tsunamis that could be similar or even worse than the 2004 Boxing Day tsunami, and that's obviously a great concern for people living in the area and makes it all the more important that proper early warning systems and evacuation plans are put together for the region.
Chris Smith: And I guess we just have to have massive respect for the awesome power of nature.
Extracted from Breaking Science first broadcast December 2008. Listen to the full episode online.
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Predict tsunamis? No.
So the claim is that we can tell that there is a tsunami every 200 years or so, and the last was about 200 years ago?
Information that could only otherwise be gathered from... historical records.
Which means that the answer to the question 'Can coral rings predict tsunamis?' is 'Yes, but not in any useful, precise or meaningful fashion'.
On the same statistical basis, we can also use tree growth rings to predict major volcanic eruptions and asteroid impacts i.e. on average, once every so often, could be tomorrow, could be another hundred years...