The quake and the tsunami
taken from Nature.com
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Published online: 20 July 2006; | doi:10.1038/news060717-14
How large was the quake?
The quake was initially reported as having a magnitude of 7.1 or 7.2, depending on the source. This was upped to 7.7 in the following days.
Is that magnitude unusual?
As Java's stunned residents have been reminded, major quakes are a fact of life in Indonesia. The archipelago is part of the Pacific 'ring of fire' — a vast, 40,000-kilometre horseshoe-shaped array of plate boundaries that also includes the US west coast. The network produces 90% of the world's earthquakes, and more than 80% of major ones, defined as those with a magnitude of more than 7.
"It's a perfectly normal event for that part of the world," says Roger Musson of the British Geological Survey in Edinburgh. "It's a major quake but nonetheless part for the course."
If quakes are that common, are tsunamis too?
Not all quakes cause tsunamis — the sea floor has to move far and fast enough to spark a wave. But tidal waves are certainly not unheard of.
In June 1994, a quake-sparked tsunami reported to be as high as 15 metres killed some 200 coastal residents in east Java. In the devastating December 2004 event, which killed some 200,000 people, water marks were reportedly found 20 metres above sea level. Although eye-witness accounts tend to be unreliable, reports from the most recent event tell of waves from 2 to 10 metres tall.
Scientists have estimated that the Indian Ocean might see an ocean-wide, 10-metre wave event (such as the one in 2004) only once every 1,000 years.
Is Indonesia prepared for this?
A tsunami warning system has recently been installed in the Indian Ocean, with instrumentation on buoys coming online this May. That system did successfully issue an alert (see Java hit by tsunami after early warning).
Lives were lost, experts agree, because of a 'last-mile syndrome' — although the global networks that keep a watch for deadly quakes and tsunamis is functioning, there is no way yet to efficiently get that information from officials out to people on the beach.
The Indonesian government was not planning to install sirens on Java until 2007, after first providing them for Sumatra, the island hit hardest by the 2004 tsunami.
"There's not enough money and manpower to do everything at once, so they took the decision — probably rightly — to do Sumatra first," says Stuart Sipkin of the US Geological Survey's National Earthquake Information Center (NEIC) in Denver, Colorado, which monitors earthquakes around the world and relays warnings to some 54,000 contact points in the event of a large tremor.
Are we getting better at detecting such threats?
Spurred in part by the 2004 tusnami, the NEIC recently replaced its 25-year-old computer system. The latest system is fed with data, via satellite, from some 475 seismic stations around the globe. Whereas before the 2004 quake it would have taken an hour to identify the size and location of a large quake, the task can now be accomplished in 12 to 13 minutes, the NEIC says.
That said, magnitude estimates produced by these computers for large quakes still need to be adjusted by an expert who can take various factors into account, including the size and depth of the fault rupture. "Once you get into the sevens or bigger, you need techniques that are not automated yet," says Sipkin.
Researchers are also working on ways to use Global Positioning Systems to more quickly calculate how far the Earth moved during a quake, to get a better, faster estimate of its true size1.
Visit our newsblog to read and post comments about this story.
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Published online: 20 July 2006; | doi:10.1038/news060717-14
The quake and the tsunami
Michael Hopkin finds out about this week's earthquake, which spurred waves that killed more than 500 people in Java, Indonesia. |
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Is that magnitude unusual?
As Java's stunned residents have been reminded, major quakes are a fact of life in Indonesia. The archipelago is part of the Pacific 'ring of fire' — a vast, 40,000-kilometre horseshoe-shaped array of plate boundaries that also includes the US west coast. The network produces 90% of the world's earthquakes, and more than 80% of major ones, defined as those with a magnitude of more than 7.
"It's a perfectly normal event for that part of the world," says Roger Musson of the British Geological Survey in Edinburgh. "It's a major quake but nonetheless part for the course."
If quakes are that common, are tsunamis too?
Not all quakes cause tsunamis — the sea floor has to move far and fast enough to spark a wave. But tidal waves are certainly not unheard of.
In June 1994, a quake-sparked tsunami reported to be as high as 15 metres killed some 200 coastal residents in east Java. In the devastating December 2004 event, which killed some 200,000 people, water marks were reportedly found 20 metres above sea level. Although eye-witness accounts tend to be unreliable, reports from the most recent event tell of waves from 2 to 10 metres tall.
Scientists have estimated that the Indian Ocean might see an ocean-wide, 10-metre wave event (such as the one in 2004) only once every 1,000 years.
Is Indonesia prepared for this?
A tsunami warning system has recently been installed in the Indian Ocean, with instrumentation on buoys coming online this May. That system did successfully issue an alert (see Java hit by tsunami after early warning).
Lives were lost, experts agree, because of a 'last-mile syndrome' — although the global networks that keep a watch for deadly quakes and tsunamis is functioning, there is no way yet to efficiently get that information from officials out to people on the beach.
The Indonesian government was not planning to install sirens on Java until 2007, after first providing them for Sumatra, the island hit hardest by the 2004 tsunami.
"There's not enough money and manpower to do everything at once, so they took the decision — probably rightly — to do Sumatra first," says Stuart Sipkin of the US Geological Survey's National Earthquake Information Center (NEIC) in Denver, Colorado, which monitors earthquakes around the world and relays warnings to some 54,000 contact points in the event of a large tremor.
Are we getting better at detecting such threats?
Spurred in part by the 2004 tusnami, the NEIC recently replaced its 25-year-old computer system. The latest system is fed with data, via satellite, from some 475 seismic stations around the globe. Whereas before the 2004 quake it would have taken an hour to identify the size and location of a large quake, the task can now be accomplished in 12 to 13 minutes, the NEIC says.
That said, magnitude estimates produced by these computers for large quakes still need to be adjusted by an expert who can take various factors into account, including the size and depth of the fault rupture. "Once you get into the sevens or bigger, you need techniques that are not automated yet," says Sipkin.
Researchers are also working on ways to use Global Positioning Systems to more quickly calculate how far the Earth moved during a quake, to get a better, faster estimate of its true size1.
Visit our newsblog to read and post comments about this story.
posted by KZIS-NL at 7:02 AM
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