Bttt...
Two weeks ago an expert warned Sumatra to expect another quake. Yesterday he was proved right. Richard Macey and Deborah Smith report.
It was 2.33am when Mark Leonard's mobile phone rang. The seismologist with Geoscience Australia was woken by a computer-generated message announcing that the west coast of Sumatra had been rocked by another massive earthquake, bringing back horrific memories of the Boxing Day tsunami.
A dismayed Dr Leonard studied the details relayed from automated seismology stations around the country.
The culprit, just as it had been on December 26, was the Indo-Australian tectonic plate that has been steadily forcing its way north at up to seven centimetres a year, for centuries. Where it collides with its neighbouring Eurasian plate, on which the island of Sumatra rides, the Indo-Australian plate is driven deep into the Earth's mantle.
Tremendous forces build up where the opposing plates jam together. The inevitable result is that sooner or later one section, unable to contain the mounting stress, must slip, triggering a powerful earthquake. It happened in one section of this region, known as the Sunda trench, off Sumatra's south coast in 1833. Twenty-eight years later, in 1861, it slipped again, just to the north. Then there was a lull until, on Boxing Day last year, yet another section of the Sunda trench ruptured near the northern tip of Sumatra, creating the tsunami that claimed almost 300,000 lives.
Two weeks ago, John McCloskey, of the University of Ulster, went public with his prediction that the region was a prime target for another major quake - and soon. People tended to think lightning didn't strike twice in the same place, he told the Herald. "But with earthquakes it's exactly the opposite."
His team had calculated that the Boxing Day earthquake had increased stresses in the adjacent area of the Sunda trench, which had not experienced a quake since 1861. At 2.09 yesterday morning, Sydney time, the inevitable happened. The plates ruptured, almost exactly where Professor McCloskey had predicted, triggering a massive 8.7 magnitude earthquake, the world's eighth biggest since 1900.
The Pacific Tsunami Warning Centre, based in Hawaii, was soon beaming out alerts, advising the "evacuation of coasts within 1000 kilometres of the epicentre". Thousands of people were evacuated in Thailand, Sri Lanka and Malaysia.
"At 4am [Sydney time] we were very concerned there would be another tsunami," Dr Leonard said. But as the hours passed there were no reports of coast beyond Sumatra being swamped.
At 4.35am tidal gauges on the Cocos Islands off Western Australian merely noted a wave 25 centimetres high, from peak to trough, passing harmlessly by. Several more waves followed in the next hour. At 8.30am the sea level at Hillarys, about 30 kilometres north of Fremantle, rose from 10 to 20 centimetres, and then settled back.
About the same time, said Dr Leonard, observers in the Maldives, in the Indian Ocean, were reporting that the sea level had risen just 20 to 40 centimetres. Late yesterday, however, news did emerge of a three-metre tsunami wreaking havoc of Simeulue. Nevertheless, as Dr Leonard studied the data, he gradually realised this was no repeat of the Boxing Day calamity, which killed 300,000 people across 11 Indian Ocean nations.
Although the quake had registered 8.7, and was still "a very, very big earthquake" by any measure, it was on the order of eight to 10 times weaker than the magnitude 9 quake that triggered the December 26 tsunami. While the numbers appear close, the force of earthquakes is measured on an exponential scale. The area of crust that shifted was also much smaller - about 50 kilometres wide and 550 kilometres long - compared with the slab of earth 1000 by 250 kilometres that slipped last year. The plate's sideway slip probably averaged only two or three metres, a quarter of the average shift in the Boxing Day rupture.
Last year's quake, noted Dr Leonard, happened on a section of faultline running north to south. The result was a tsunami that rolled out across the Indian Ocean, heading due west, slamming into Sri Lanka, India and finally Africa. The faultline that shifted yesterday runs from the north-west to the south-east, parallel with Sumatra's coast. This time the tsunami headed south-west, out into a largely empty ocean. "This quake was probably due to happen sometime in the next decade," said Mr Leonard, confessing, "I was not expecting another one so soon." He speculated the Boxing Day event had "probably nudged it forward ... it must have been ready to go".
The seismologist declined to punt on what would happen next, saying he did not believe earthquakes could be predicted. "I would not be surprised if there is another 9 magnitude quake off south-western Java ... some time in the next couple of centuries."
Professor McCloskey was not so cautious. "Unfortunately, I'm not at all surprised by today's news," he told ABC radio. He said the next stretch of Sumatra's undersea Sunda trench would now be under additional stress from yesterday's quake. It was too early to say whether this would trigger another quake in the region that has not ruptured since 1833.
He also predicted this quake could increase stress on a faultline running down the centre of Sumatra and under the city of Banda Aceh, already destabilised by the Boxing Day quake.
Ping.
Cheap b@stards. /sarcasm
Semper Fi
".... caused by the Boxing Day disaster"
I've never heard the last disaster referred to as the Boxing Day disaster. I had heard it referred to as the Christmas Day disaster which I am not sure if was exactly factual for any region of the globe. Would have to admit that Boxing Day sounds more PC.
Opening check book, sending vast amounts of money for helping to gas up the UN choppers, feeling much better.
Looks like there are going to still be a lot of people in need...
Wow! I actually scooped this last night on the quake thread. Nobody believed me at the time.
I hope that the US keeps the checkbook CLOSED this time.
It's amazing that in this modern age of instant communication that there are still pockets of the world so isolated that it takes a full day to realize a catastrophe has struck.
explain please...25 cm is about 10 inches, how does that translate to an 11 foot wave.
ping
>>>Kyoto and Agence France-Presse news agencies reported.
Kyodo!
They should change their name from Sinabang to Sinhasconsequences.
A nine foot wave is just good surfing. No one should get hurt by the break on this one.