Fiona MacDonald, Science Alert 9 Oct 09;
For the past ten days the Ring of Fire has been releasing its fury on the Pacific Islands and the towns and cities of Sumatra, Indonesia.
There have been at least five major earthquakes in the notorious region in just a little over a week – one which caused a tsunami that obliterated entire towns on the islands of Samoa. Combined, these natural disasters have killed at least 1470 people, and the number is expected to rise as the search for survivors comes to an end and water shortages and disease affect the regions.
As the scale of the disasters magnify, it’s hard not to question why this has happened. What caused so many earthquakes to occur in the one region in such a short space of time - was it a coincidence, or a linked chain of events? And with all of our technology, why couldn’t we get the warning out in time?
The earthquakes all occured along the notorious Ring of Fire. The Ring roughly circles some of the world’s most picturesque islands and countries – like Samoa, Vanuatu, Tonga and Indonesia, but it is a far from stable location. Eighty per cent of the world’s largest earthquakes occur along the Pacific Ring of Fire, and on boxing day 2004 a massive plate movement on the Ring caused a tsunami that killed around 300,00 people.
Despite its bad reputation, the number of large earthquakes that have occurred in the region over the past ten days has shocked scientists and the media, and have caused them to question the link between the events.
Coincidence or connected?
The earthquakes off the coasts of Samoa and Sumatra, which occurred on the 29 and 30 of September, have been the most closely scrutinised. Despite the fact that they occurred within a few hours of each other, physically the earthquakes were very different.
Notably, the Samoan earthquake was close to the surface of the seabed and caused a tsunami, whereas the Sumatran earthquake was deeper and did its damage by violently shaking the Indonesian island.
Despite their differences, both earthquakes occurred on the Australian plate, and researchers from the University of Queensland have suggested that one may have triggered the other. However, many are sceptical. Samoa is 6,400 kilometres from Indonesia, and stress from Earthquakes usually only travels around 600 kilometres.
“There is no causal link that we know of between Sumatran earthquake and the Samoan earthquake although both are on (different) boundaries of the Australian Plate,” said Kevin McCue, President of the Australian Earthquake Engineering Society.
However, a study published in Nature on Thursday 1 September revealed that earthquakes can weaken faults a great distance away – the team from the USA suggested that the 2004 earthquake which caused the Boxing Day tsunami may have weakened the San Andreas Fault 8000 km away.
In light of this discovery, it is possible that the two quakes were linked - but McCue argues that it is far more likely that the Sumatran earthquake was triggered by the Boxing Day earthquake in 2004 rather than the Samoan one the night before.
“There is a strong link between the Sumatran earthquake and the December 2004 great earthquake on an adjacent segment of the same plate boundary. It is certainly within a fault length of the 2004 earthquake, the distance within which stresses have been affected by reworking of the faulted boundary,” said McCue.
That doesn’t mean that the Samoan earthquake, measuring 8.0 on the Richter scale, had no effect - it is likely that it triggered the three earthquakes on 8 October off the coast of Vanuatu, according to McCue.
These latest quakes caused a tsunami that had people fleeing the coast in New Zealand and Australia and Pacific island locals clambering for high ground, before the warnings were called off.
Is this the beginning of the end?
So what does it all mean? Are the multiple earthquakes a sign of the beginning of the end. And did our impact on the planet cause them?
After watching movies like The Day After Tomorrow it’s not hard to assume the worst, but McCue argues that, although tragic, the disasters of the past week aren’t unheard of in the history of the planet.
“The current levels of activity are unusual but not uncommon. Events of this frequency and magnitude (and worse) have occurred in the past and will continue to do so for millennia. The presence of humans has not changed the intensity and frequency of these large, catastrophic events. The surface of the earth will continue to move and change, and it will do so more dramatically and more often in the areas that are already known to us as highly active,” said McCue.
It is small comfort to know that this is one disaster we may not have brought upon ourselves; however it is devastating that we can now explore Mars and find water on the moon, but we still cannot protect ourselves from changes on our own planet.
Where will the next large earthquake hit?
Although we know a lot more about the movements of the Earth's tectonic plates and 'weak spots' than we did in the past, we still can’t predict when earthquakes will happen. We can look at which faults are weakened and expect movement in that region, but there is no knowing when this will occur. In the case of the earthquake that caused the Boxing Day tsunami in 2004, scientists predicted that the surrounding faults would be weakened as a result, but it took five years before another large earthquake struck.
Further research may open up new ways for us to predict earthquakes, but the planet will always be out of our control, according to McCue. We must focus on developing early warning systems and educating residents in high-risk areas on when to find shelter, he adds.
Preparing for the worst
The Ring of Fire isn’t out of danger now by any means, says McCue. The floor of the Indian Ocean is being dragged down below Indonesia, and this is going to continue to cause jerks that can result in earthquakes and tsunamis.
“This sequence is not abnormal for a plate boundary, and whilst it is not possible to guess where earthquakes will happen in the near future, countries from Papua New Guinea to New Zealand would probably be wise to dust off their response plans.”
One thing that is clear from the events of the past week is that it is dangerous to wait for official warnings, according to McCue.
“How long before we can get this simple message to all inhabitants of and tourists to the south-west Pacific islands and south-east Asia? If you are near the sea and feel a large earthquake, then immediately make for a spot at least 10m above the high water mark and wait there for several hours. The earthquake shaking is the best tsunami warming you will get, no good waiting for the phone to ring or a warning to be issued on the radio,” said McCue.
“That education should start in the schools,” he added.
While we clean up after the damage unleashed by the earthquakes of the past ten days, the best that we can do is to understand that this disaster is not a random coincidence or a one off - on the timeline of the planet this is a normal event.
Although we will never stop earthquakes, we can’t be too cautious, according to McCue. People need to be prepared for the worst and know when to get to safety. As we have witnessed too many times over the past five years, waiting for a warning can be the difference between life and death.
