Australian Geographic BY:NATALIE MULLER | MAY-11-2012

Predicting tsunamis is a complex task, but scientists' efforts in improving warning times are saving lives.

IN 2004, A MAGNITUDE 9.1 earthquake off the coast of northern Sumatra, Indonesia, generated the worst tsunami in recorded history. With more than 230,000 people dead and many more hundreds of thousands injured and homeless, this natural phenomenon wreaked widespread destruction.

At the time, people were caught off guard - the world had not seen a massive tsunami for generations and did not recognise the danger. Since then, a heightened awareness has brought tsunamis into consciousness, with almost every earthquake reported having an associated tsunami risk attached to it.

The enormous tsunami in Japan in March 2011 further highlighted the power of big tsunamis. But the most recent magnitude 8.6 earthquake off the coast of Sumatra, Indonesia on 11 April, 2012 - which didn't generate a destructive tsunami - showcases just how complex tsunami generation can be. Not to mention their prediction.

A cluster of earthquakes?

It takes a massive disruption of the Earth's crust beneath the sea floor to displace enough water to generate a tsunami. Once in motion, these earthquake-triggered waves can race up to 1000km/h in open water, devastating coastlines in their path.
But they're rare. On average, destructive tsunamis occur twice a year, and tsunamis that cause ocean-wide devastation, like the one in 2004, happen only once every 15 years, on average.

Paul Somerville, deputy director of Risk Frontiers Natural Hazards Research Centre at Macquarie University, Sydney, says it's significant that there have been a series of large earthquakes triggering tsunamis in recent years - Sumatra in 2004, Chile in 2010 and Japan in 2011.

"We're interested in whether it shows that these earthquakes cluster in time or not, and that's a raging debate at the moment," he says. "The previous big earthquakes all happened in the late 1950s, 1960s, and since then there haven't been any magnitude 9 earthquakes."

Tsunami warning system for the Indian Ocean

Historically, over 80 per cent of tsunamis have happened in the Pacific, especially around the Ring of Fire, and for decades there's been a Pacific Ocean Tsunami Warning System keeping an eye on the region.

One of the reasons for the huge loss of life in 2004 was the absence of such a system in the Indian Ocean.

"A lot of people died in places like Kenya, India, Sri Lanka, Thailand, Maldives, Madagascar, Tanzania," says Daniel Jaksa, co-director of the Joint Australian Tsunami Warning Centre (JATWC) at the Geoscience Australia hub in Canberra. "It was 15 hours' travel time [for the tsunami to reach] Africa, so those people should have been warned. If it happened now, I'd be amazed to see any deaths away from the epicentre."  

In 2005, the Indian Ocean community set in motion a plan to develop their own warning system, and there are now centres monitoring potential tsunami threats in Australia, India and Indonesia.

Predicting tsunami waves

Like any earthquakes, there's no way of predicting when tsunami-causing quakes will strike, but thanks to these early warning systems, it's now possible to get word out about an approaching tsunami within minutes.

Not all big underwater earthquakes will cause big waves, but Daniel says a tsunami will generally happen if there's a significant earthquake (magnitude 7 or above) in a subduction zone where the tectonic plates meet.

The April 2012 magnitude 8.6 earthquake off the coast of Sumatra didn't generate a tsunami because it happened away from the plate boundary. And, unlike the 2004 earthquake, which forced a 1300km-long chunk of the sea floor upward, the more recent earthquake only caused the two plates to grind together horizontally. 

Still, this underwater seismic activity put the Indian Ocean tsunami warning system to the test. The earthquake struck on 12 April at 08:38 GMT, and within five minutes, the Indonesian Meteorological Service had issued a tsunami warning across the region. This was followed minutes later by warnings from other centres in India and Australia, as well as from Japan's Meteorological Agency and the Pacific Tsunami Warning Centre in Hawaii. 

People closest to the epicentre scrambled to higher ground, expecting a repeat of the 2004 disaster, while warnings were in place along Africa's west coast, Thailand, India, Sri Lanka, Indonesia, the Middle East and many Indian Ocean island communities. But the anticipated giant tsunami never came. 

Scientists working at the region's warning centres downscaled the threat after local sea level gauges and deep ocean sensors confirmed no huge tsunami had been generated.

Profiling an incoming tsunami 

The JATWC has an arsenal of tsunami-tracking tools at its disposal so it can alert the Bureau of Meteorology about any risk within 15 minutes of a quake occurring.

DART (Deep-ocean Assessment and Reporting of Tsunami) buoys moored to sensors on the sea floor monitor pressure shifts caused by a passing tsunami and beam changes in sea-surface height back to scientists.

"This gives an idea of the speed, which [scientists] can estimate very closely based upon a whole series of pre-computed scenarios and tsunami travel times around the ocean," says James Goff, co-director of the Australian Tsunami Research Centre and Natural Hazards Laboratory at UNSW. 

The tsunami scenario database is one of the more recent additions to the warning system. After an earthquake, the closest scenario is chosen from thousands of situations, and scaled to match the tsunami's magnitude. This has made it much easier for scientists to build a detailed picture of a tsunami's behaviour, such as how tall the waves might be (amplitude) and where they're headed. But even with current technology, it's difficult to predict what the impact and magnitude of the waves will be on land, says James.

"For tsunamis generated a good hour or so away from the coast, there is now a system in place," he says. "Of course, tsunamis can be generated by other mechanisms such as landslides and volcanoes, and also if a tsunami is generated close to the shore then there will be little warning anyway and the system cannot help in those cases."

World-first warning system

Geoscience Australia is currently building a world-first warning system out of an array of seismometers in the remote Pilbara region of WA that aims to make more accurate tsunami predictions possible. The instruments will monitor earthquakes in the Indian Ocean and beam seismic signals from the initial rupture to the warning centre.

"Essentially what we're doing is defining the epicentre," says Daniel. "Mapping that rupture...defines very much what type of tsunami forecast you can do in terms of arrival times, [and] locations of coastline that are impacted by the tsunami." 

But gathering data about an approaching tsunami is only half the battle. The other half is educating people about how to respond to warnings. Tsunamis may be rare and unlikely events, but adequate preparation could save thousands of lives.
James says Japan is probably the most tsunami-prepared nation, while Australia is at the opposite end of the scale. 

"The technology is great but it's the last mile that's missing - in other words, you can give the message to people, but unless they understand it and know what to do, then nothing has changed," he says. "We spend lots of money on the equipment and technology but very little on what matters most - the people." 

Fox News Mocks Security Threat To Small Islands Posed By Climate Change

 

Camelia Pasandaran | November 19, 2010

Jakarta. The tsunami that devastated the Mentawai Islands off West Sumatra last month featured waves much larger than would normally have been expected from the magnitude 7.7 earthquake that spawned it, according to a tsunami expert.

Jose Borrero, from ASR Ltd., a marine consulting firm, said on Friday that the finding was extraordinary.

“We were extremely surprised by the size of the waves on one of the small islands offshore of Pagai,” he said at a press conference at the office of the presidential advisory council.

“We found evidence that the tsunami waves reached a height of 17 meters, which was much bigger than we had expected to find,” he said.

Borrero, who is also a researcher at the University of Southern California’s Tsunami Research Center, said that while most residents of the islands were aware of the potential for a tsunami, the majority had been caught unawares by the relative weakness of the Oct. 25 quake.

“They knew that earthquakes are associated with tsunami, and that they should be aware of evacuating if they felt a strong earthquake,” he said.

“However, this earthquake didn’t feel that strong to them, especially when compared with previous earthquakes in the area. So some people didn’t evacuate immediately upon feeling the earthquake. It wasn’t until they actually heard the sound of the waves coming through the trees and tearing down the forest that they actually knew that they had to go.”

He said that because Indonesia would always be prone to tsunamis, residents should learn to read the signs.

“Basically, tsunamis and earthquakes are part of natural life,” Borrero said.

“You can’t live in fear of them. It’s best to understand them and work with a national system. By understanding them, we have the chance for survival. This isn’t something to be afraid of, but to be aware of, to know what to look for,” he said.

At least 461 deaths have been confirmed as a result of the tsunami, while 43 others remain missing and are feared dead.

The waves also rendered nearly 8,000 people homeless.

Hermann M. Fritz, a tsunami expert from the Georgia Institute of Technology in the United States, said the real measure of an earthquake’s potential for causing a tsunami in tectonic subduction zones such as the Mentawais, was not the perceived strength of the quake but rather its duration.

“How long the quake lasts will indicate its potential for a tsunami,” he said.

“If you feel the shaking for more than 30 seconds or a minute, it’s important to evacuate immediately.”

Danny Hilman, a researcher at the Indonesian Institute of Sciences (LIPI), said the Mentawai quake lasted more than a minute.

However, he said most local people interviewed by the experts had said that at the time of the quake they only felt a swaying motion, and thus did not feel the need to evacuate.

He said that in the case of Mentawai, while the quake registered at a magnitude of 7.7, its long duration meant it was more like a magnitude 8 temblor.

When a tsunami ripped through the Indonesian island chain, it was just another blow for a long-marginalised community
Cain Nunns
Guardian Weekly,     Tuesday 16 November 2010 16.29 GMT

 
People walk where hundreds of homes once stood in the tsunami-hit Muntei Baru Baru village. Photograph: REUTERS
Jasmen Samaloisa heard the panicked screams of his fellow villagers, but not for long. A five-metre high tsunami washed them away as it inundated Muntei Baru Baru, his remote community on the south-west coast of the Mentawai Islands.

"It sounded like a jet engine on take off. We were 600 metres away from the village when it came, and we still couldn't hear ourselves think," Jasmen said. His family was one of the few to escape to the hills after a 7.1 magnitude earthquake rocked the Indonesian island chain on 25 October. (The islands, put together, are 20% bigger than Bali.) The kilometre-wide wall of water that followed the quake tore apart his village of thatched houses, killing 112 out of 154 residents, including five of Jasmen's extended family.

It took Jakarta and the provincial government in West Sumatra nearly a week to deliver aid to the ruined communities on the islands, about 150km off the West Sumatran coast; 454 residents had died, 54 were missing and more than 18,000 were homeless.

Critics of the government's emergency response say it was typical of the way Mentawais communities have been sidelined by powerful vested interests ever since dictator Suharto's New Order era. Activists and community leaders make it clear that there was a Suharto-backed policy of "modernising the Mentawai" and forcibly relocating their villages from the forests to coastal areas. This created social, environmental and economic problems.

"Since the 70s there has been widespread cultural discrimination against the Mentawai. Their cultural symbols, traditional meeting houses and villages were burnt by the government when they were forced to relocate," said Frans Siahaan, a director of rights group Yayasan Citra Mandiri.

"The government called it the 'relocation of alienated people'... But I don't see how they were alienated. They were perfectly happy. If anybody is alienated, it is the people in Jakarta, who are alienated from the rest of the country's social and cultural situations."

Behavioural change programmes were set up to teach the Mentawai to "assimilate to a developing Indonesia". Environmentalists say that these programmes really masked plans by Suharto's family members to open the forests to Jakarta-controlled logging companies.

Strip-logging of the islands became the norm rather than the exception. When environmentalists won a rare concession to turn half of the northern island of Siberut into a protected national park, palm oil concessions were granted to allow the owners to "clear tracts" for plantations. They were never planted. Instead, the logging interests would "spot mine" forests and move on.

"Illegal logging is a massive problem in Indonesia only because of weak law enforcement. But in the Mentawais, we are special. We have had the military, the police, district officials and port officials all involved in illegal logging," said Zuhi Saad, an environmentalist.

His colleagues say that the uncontrolled rates of deforestation in Indonesia, which have turned it into the world's third-biggest producer of greenhouse gases, are the result of poor governance, lax enforcement and widespread corruption in governmental departments, law enforcement and the judiciary.

"They have completely destroyed the forests. It is mostly secondary growth out there now," Zuhi said.

The logging interests do not build infrastructure, such as roads and telecommunications, because these would make areas more visible. They have left only track-scarred forests and an airport in Siberut that cannot be used by island residents.

There are no proper roads on the islands, and sea transport between the islands is limited and dangerous, so there is no access to the two underfunded medical facilities to serve a population of about 35,000. Communications are poor and government offices are crumbling.

Worse, the Mentawai have been denied access to their ancestral home. "They had lived in those forests for thousands of years and when the government designated them as state-owned, it forced the Mentawai to obtain land acquisition certificates from the ministry of forestry in order to use them," said Frans. "Of course, these were virtually impossible to get."

The islands have been despoiled of enormous sums in resources by the loggers, fishermen from the outside who have used dynamite to plunder the stocks of the reefs, and a famous, although unregulated, surfing tourism industry. Yet 70% of island residents live below the poverty line, and barely 23% make it to the end of middle school, in part because half of the children are malnourished, with stunted growth.

There are persistent claims that the central and provincial governments deny the islands funds and resources because 90% of the Mentawais are Christian, whereas West Sumatra is 90% Muslim.

Island Aid + Troppodoc have a team in Mentawai delivering aid and running clinics. This is a proven approach that we have developed over the past 5 years in Aceh, Nias and the West Sumatran earthquakes. In Mentawai the greatest challenge is transport. The islands have only rough logging trails and so aid must be delivered by boat. The scale of this disaster is much smaller than Aceh and there is a public ferry service to the main ports so we have mobilized our small cargo motor boat, 2 rented motor bikes and our speedboats to maintain support to some of the worst hit villages.

This is Island Aid’s priority list to support Mentawai tsunami survivors:
    ◦    7 ton Cargo / Transport Boat -  including fuel, crew, food for crew US$100 /day
    ◦    6m Speedboat with 40HP Outboatd including fuel - US$25 /day
    ◦    Hygiene Kit - Soap, bucket, bowl, tooth brushes, towel - US$7 /family
    ◦    Tool Kit - Handsaw, Jemmy bar, Hammer, Assorted nails. - US$15 /family
    ◦    Kitchen Kit - Wok, Saucepan, cutlery, mugs - US$25 /family
    ◦    Shelter Kit - Kerosene Lamp, Tarp, rope - US$25 /family
    ◦    Motorbike hire and fuel US$15 /day

The team will work in the Pagai area for several days and then move to South Sipura.
Your help will make a big difference.

Cyclonic squall slams into the Sumatran coastline yesterday afternoon. Winds of up to 65knots were measured in Mentawai.

BNPB and Indonesian Navy, Red Cross together with Mercy Corps, Surf Aid and several other large NGOs have mobilized a fleet of boats to deliver emergency aid to west coast villages. IOM and other UN agencies are funding helicopters and a 100ft ship to improve aid delivery. The scale of the emergency response is very encouraging but cyclone Anggrek continues to pound the area with gale force winds and heavy seas. Our donor partners have decided not to fund any additional boats at this stage but focus on purchase of shelter materials and tool kits.

Island Aid is now working with Troppodoc to establish a clinic and aid post in South Sipura at Katiet. Most Government shipping and aid is now focused on Sikakap 50miles south and very little support is arriving in South Sipura. A detailed funding proposal is being prepared but the cost of this aid post will be far lower than chartering a boat. Our cargo boat Yelsie and beach landing boats will be moved to Katiet when the weather permits.

We are also working on a second project aimed at saving lives in coastal communities in the Mentawais and along the west coast of Sumatra. The "Tsunami Survival Pod" project requires modest funds for prototype testing and development. Once tested donors will be able to donate a TSP unit to families in target communities.

There is no point trying to send material goods to Padang because of the shipping costs and delays. We can source everything we need in Padang.

What is needed is cash donations and our Pay Pal button is set up in the right hand column on each page of this website.

Virtual and field volunteers with appropriate skills are welcome to apply to Island Aid via our "Contact" page on our main website www.island-aid.org.

Please tell us about your skills and experience. Field volunteers will be asked to contribute to cover the cost of their accommodation in Padang or Mentawai.

Thanks, Rick

Jakarta Globe - Today
Nivell Rayda | November 01, 2010

Tuapejat and Sikakap. Despite being the capital of Mentawai district, tsunami relief efforts in Tuapejat are apparently in chaos, with food and medical supplies not only arriving late but also spoiling due to mishandling and negligence.

The first batch of government aid arrived in Tuapejat, on the island of Sipora, only on Friday afternoon, a full four days after the earthquake-triggered tsunami swept the group of islands off the western coast of Sumatra. The supplies were routed from Sikakap, on a small island to the south where relief efforts are being coordinated.

But about 20 percent of the ton of rice earmarked for the victims was drenched by seawater and heavy rains, while many cardboard boxes containing instant noodles and milk were also destroyed by water.

Some of the supplies have been going missing in less accidental ways. “Don’t tell anyone,” said one worker as he stuffed two tins of sardines in the pocket of his trousers. Other workers were spotted drinking bottled water meant for the victims. Seeing the drenched rice, a senior police officer overseeing the shipment called over residents waiting for passenger boats in the harbor.

“These sacks of rice are soaked, it will rot before it even gets to the victims. Give it to these people here,” the officer told the workers.

At least 20 sacks, each containing at least 10 kilograms of rice, were handed out to the people of Tuapejat.

“Can we also keep the blankets that were drenched in water?” a local asked a worker.

At least 96 people are still missing in the wake of the 7.7-magnitude earthquake that drove a tsunami onto the Mentawai Islands on Oct. 25, and the death toll now stands at 449. Mentawai’s four main islands were devastated by the waves, displacing almost 13,000 people.

Sikakap on North Pagai Island, which along with South Pagai were the worst-hit, has become the hub for aid shipments.

But as supplies and volunteers began to flood in late last week with very little coordination from the central government, relief efforts quickly became chaotic. No one appeared to be recording which villages received aid, nor was there anyone in charge of directing new volunteers.

With no official in sight to coordinate the aid shipment, workers piled boxes of instant food on a wet ship floor, soaking the packets and leaving the contents to be scattered and stepped on by laborers unloading other cargo.

“We don’t know how much is being sent. We weren’t told the exact amount. All we know is that there is one ton of rice,” said Adek Simangunsong, a local volunteer.

“The aid was supposed to be here on Thursday, but strong currents and high waves delayed the shipment.” Bad weather had forced the relief ship to delay leaving Sikakap until Friday morning, four days after the quake.

The roughness and remoteness of the area, as well as the limited number of people affected, means that Sipora Island is virtually untouched by government aid.

“Everything is being sent to Sikakap. You can say that the aid sent to Sipora is not surplus,” Adek said. “There are many villages that still haven’t received anything. We are having trouble accessing them. Many of our ships and boats were forced to turn back to Tuapejat because of the rough seas.”

On Saturday, two boats carrying volunteers and aid capsized off the coast of Sikakap as locals reported waves up to four meters high.

The 15 volunteers aboard survived, but no one seemed to be in charge of their safety either.

Surung Matua Sinaga, chairman of the West Sumatra Disaster Relief Agency (BPBD), said his job was only to distribute aid to the victims and to coordinate volunteers, but said that when he heard the news of the capsized boats from two field officers in Mentawai, he told them: “It is not my responsibility.”

Surung said the agency responsible for coordinating volunteers was the Relief Operations Control Center (Pusdalop), in the West Sumatran capital of Padang.

But Depi, a Pusdalop official, thought otherwise. “We haven’t had any information about this [capsizing] incident. Our job is to register volunteers and journalists traveling to Mentawai. Once they get to the islands, it is the field coordinator’s job to direct them and monitor where they are going,” she said.

She didn’t know who was in charge on any of the islands.

Note from Island Aid. The UN/OCHA is saying that a NZ NGO, Surf Aid are in charge of coordination of all NGO efforts in Mentawai and they have been appointed to do rapid assessment coordination. See www.mentawairesponse.org

Current satellite image courtesy of Wunderweather and NASA. Mentawais are top center.

Anggrek started to form a few days ago as a revolving tropical storm close to the Mentawais and it has virtually shut down boat operations between Padang and the tsunami impact area.

The birth of Cyclone Anggrek on Sunday 00hrs. Storms have been lashing the area for the past 5 days and are now intensifying.

Island Aid and donors have decided to cancel the Naga Laut mission. Surf Aid have arranged NZ Government funds to charter 6 boats and they are now in the Mentawais ready to deliver aid and medical teams when the weather moderates. The UN is considering the use of helicopters but the weather looks like it will make that option unworkable for the next few days. We believe that donor money is better spent on aid and shelter supplies for the months ahead. We are now focused on establishing land based clinics and using Navy or Government vessels to cross the Mentawai Straits. We are drawing up new plans together with Tropodoc and other NGOs with medical capacity.

The first cyclone swell hitting beaches in Padang with another squall approaching from the west.

http://www.gitews.org/index.php?id=23&L=1

http://environment.newscientist.com/channel/earth/tsunami/mg19526215.700-gps-shield-will-mean-faster-tsunami-alerts.html
GPS shield’ will mean faster tsunami alerts  /  15 September 2007

A “GPS shield” that works in real time could save lives by quickly warning of potential tsunamis. The German-Indonesian Tsunami Early Warning System (GITEWS) is being developed by a team led by Jörn Lauterjung of the National Research Centre for Geosciences in Potsdam, Germany. Unlike a GPS method proposed last year, which detects seismic waves transmitted through the Earth’s crust to distant receivers, the new ground-based system takes real-time measurements of vertical ground motion – the type of fault movement more likely to produce tsunamis (Journal of Geophysical Research, DOI: 10.1029/2006JB004640). To protect the Indian Ocean region, the proposed shield would include an array of 18 GPS stations.

http://www.agu.org/pubs/crossref/2007/2006JB004640.shtml

ABSTRACT
“The 2004 catastrophic Indian Ocean tsunami has strongly emphasized the need for reliable tsunami early warning systems. Another giant tsunamigenic earthquake may occur west of Sumatra, close to the large city of Padang. We demonstrate that the presence of islands between the trench and the Sumatran coast makes earthquake-induced tsunamis especially sensitive to slip distribution on the rupture plane as wave heights at Padang may differ by more than a factor of 5 for earthquakes having the same seismic moment (magnitude) and rupture zone geometry but different slip distribution.

Hence reliable
prediction of tsunami wave heights for Padang cannot be provided using traditional, earthquake-magnitude-based methods. We show, however, that such a prediction can be issued within 10 minutes of an earthquake by incorporating special types of near-field GPS arrays (“GPS-Shield”). These arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than the seismic moment if placed above the rupture zone or are less than 100 km away of the rupture zone. Stations in the arrays are located as close as possible to the trench and are aligned perpendicular to the trench, i.e., parallel to the expected gradient of surface coseismic displacement. In the case of Sumatra and Java, the GPS-Shield arrays should be placed at Mentawai Islands, located between the trench and Sumatra and directly at the Sumatra and Java western coasts. We demonstrate that the “GPS-Shield” can also be applied to northern Chile, where giant earthquakes may also occur in the near future. Moreover, this concept may be applied globally to many other tsunamigenic active margins where the land is located above or close to seismogenic zones.”

SUBSCRIBE TO THE NEW GFZ QUAKE ALERT by sending an empty email to: eq_warning-on@gfz-potsdam.de
For more info go to:  http://geofon.gfz-potsdam.de/geofon//seismon/globmon.html

http://www.earth.northwestern.edu/people/seth/research/
http://www1.uea.ac.uk/cm/home/schools/sci/env/research/seismic

MAGIC NUMBER > 8.5  =  TSUNAMI
http://technology.newscientist.com/article/dn9456
GPS can help give early warning of tsunamis
BY Tom Simonite  /  30 June 2006

Using GPS (global positioning system) data to measure how points on land move following an undersea earthquake could help geologists decide if the tremor will cause an ocean-wide tsunami. Combined with existing tsunami warning systems, the data could speed up decisions about whether to issue an alert and avoid false alarms, say US researchers. Tsunami warning systems use a combination of seismometers to measure tremors and ocean buoys to spot pressure waves. But it is difficult to pinpoint the exact strength of an undersea quake. This can cause problems for those deciding whether to issue a warning, says Seth Stein, a geophysicist at Northwestern University in Illinois, US. “The hardest job is to distinguish quakes that are big from those that are dangerously big,” he told New Scientist. “Richter scale 8 is quite a big earthquake, but about 8.5 is the magic number. Above that, ocean-wide tsunamis start to happen.” GPS measurements of points around a quake could determine more quickly than current methods whether this threshold has been exceeded, he says.

Vague measurement
The 2004 Sumatran quake – which caused the Asian tsunami – was eventually measured at between 9.2 and 9.3, but seismometers can initially only determine whether a quake is larger than about 7. “It normally takes a couple of hours to know whether it was over 8.5 or not,” says Stein. “Limits on how much energy can be stored in rock mean the first body waves of a quake don’t get bigger, but just ring for longer.” Taking GPS measurements of points on land around a quake can answer this crucial question within 15 minutes, according to a study by Stein and co-workers from the University of Nevada, US. To prove the technique can work, they used GPS data recorded during the first 15 minutes of the 2004 Sumatran quake, which made it clear the tremor would go on to cause a devastating tsunami in the Indian Ocean.

Millimetre accuracy
Software developed at NASA’s Jet Propulsion Laboratory was used to measure the position of 38 GPS stations between 300 and 7500 kilometres from the quake’s epicentre northwest of Sumatra. Knowing how these stations moved to within 7 millimetres makes it possible to measure long-frequency waves from the quake and estimate its size. “Using that 15 minutes of data it was possible to say the quake was a 9.” This was very close to the 9.2 or 9.3 figure eventually determined for the quake, says Stein. “We think this would be a useful third component to the existing tsunami warning system. By taking out the guesswork it could make it more accurate and avoid false alarms.”

Geophysicist Paul Burton at the University of East Anglia, UK, agrees, but cautions that the system’s effectiveness will depend on the location of the earthquake. “It’s feasible but might not help in all circumstances.” If the GPS stations available are not located in the right place relative to the epicentre, satellite measurements may not be that helpful, he says. “Another consideration is whether high-tech systems for tsunami warnings will be here in three to four hundred years time,” says Burton. “Educating people right now and making sure the knowledge about what to do is kept alive can make a huge difference. For example, a 10-year-old British girl saved many lives during the Indian Ocean tsunami when she remembered the early signs of a tsunami from her geography lessons.”