An earthquake measuring 8.1 that hit near Samoa at 3.48am AEST this morning (Wed 30 Sept 09) has generated a tsunami and killed dozens. Further quakes and aftershocks measuring between 5 and 6 have hit the region in the following hours. Below Australian experts respond.
For comments focussing on the earthquake off Sumatra click here.
The Geoscience Australia website has good basic information about earthquakes and tsunamis. There is also more information about this morning’s earthquake at GeoNet in New Zealand.
The US Geological Survey have produced a summary poster of this event.
(updated Thu 1 Oct at 5pm AEST)
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Kevin McCue is President of the Australian Earthquake Engineering Society (Canberra based).
“It is very depressing to see the same old sequence unfold in Samoa and Indonesia, Australia responds after yet another natural disaster strikes in the region, and Australia has developed a very efficient response strategy.
What a shame the Australian Government isn’t proactive, working with our neighbours in the disaster prone areas of the south west Pacific and Indonesia to build their own resilience to disasters rather than waiting to be asked to help after the event. Papua New Guinea hasn’t updated its earthquake loading code in the last 30 years, its earthquake monitoring network has collapsed, Vanuatu lost its earthquake monitoring capability in a fire several years ago, the Fiji earthquake monitoring system needs an upgrade. The Australian government does nothing, waiting to respond when these glaring deficiencies are highlighted in the next earthquake, tsunami or cyclone.
What could/should Australia do?
Sit down and talk with the neighbouring governments and run through a prepared checklist; what is the state of monitoring equipment? Is the building code effective? Is the building code followed? What education is provided about national disasters? How resistant are hospitals and schools to natural disasters especially earthquakes and tsunamis?
Tsunami warning systems are useless in most of the countries like Indonesia and Papua New Guinea because the lead time is too short, far better to educate people to make for high ground immediately after they feel shaking that lasts more than about 30 seconds. That education should start in the schools. Most of these countries don’t have adequate books and teaching material.
Australia and New Zealand have just updated their own earthquake codes and could easily export them to neighbouring countries with modification, with help. Australia could have in place an education system to make it easy for students from these countries to come to Australia for secondary and tertiary education in earth sciences and engineering, medicine and communications etc. Australia could lead by ensuring each country has links to an operational regional earthquake and tsunami monitoring network with in-house seismographs and tide gauges. In particular each country could have sufficient networked strong motion seismographs to provide vital information for the new loading codes.
There is a lot Australia could do between disasters rather than sitting waiting, turn the ‘could’ into ‘will’.”
Ian Manock is Emergency Management Courses Coordinator at Charles Sturt University, NSW.
“The widespread impact of the tsunami on Samoa will no doubt have emergency service agencies in the country pushed to their limits and beyond. Here in Australia we make widespread use of volunteer support to the emergency services and emergency management agencies during and in the aftermath of disasters. When there is widespread impact on the population this volunteer support is reduced. In a country such as Samoa that is developing and which has a small population, the impact of a widespread disaster will mean there is additional stress placed on the emergency services and government agencies responding to the event. I would expect that the Samoan government will be asking for disaster relief assistance from Australia and New Zealand in the form of financial aid and post-disaster relief rehabilitation and reconstruction.
“Immediate post-disaster recovery issues that will need to be addressed will be the urgent need for food, clean water, accommodation and public health related services for those affected by the disaster. The medium to long term issues of clean up, restoration, rebuilding, re-establishment of businesses and the tourist industry that might have been affected by the disaster will also need to be addressed.”
Gary Gibson is Senior Seismologist at Environmental Systems and Services, based in Melbourne, and is Chairman of the Executive Committee of the International Seismological Centre. He is an Honorary Research Associate in the School of Geosciences at Monash University.
“The earthquake south of Samoa this morning occurred at 06.48 AM Samoa time (03.48 AM Eastern Australian Standard Time). It was located 200 km south of Samoa, north of Tonga and northeast of Fiji, and was at a shallow depth.
The earthquake had a moment magnitude of about 8.0, which corresponds to a rupture within the earth that may be 200 to 300 km long, with a depth of 100 to 200 kilometres, with one side of the fault moving 4 to 7 metres relative to the other. This is quite large enough to deform the sea floor and generate a tsunami, but the size and pattern of the tsunami depend on the amount and orientation of the sea-floor deformation.
The earthquake magnitude and deformation were much less than in the rare huge earthquakes of magnitude 9.0 and higher, such that off Chile in 1960, and the Boxing Day 2004 earthquake off Sumatra. The fault length for those was greater than 1000 kilometres, and the plates moved 10 to 20 metres or more relative to each other. For the Samoa earthquake, this meant that a devastating tsunami could be produced locally, but it was unlikely to seriously affect countries on the boundary of the Pacific.
The earthquake occurred at the north end of a major north-south tectonic plate boundary, the Tonga-Kermadec Trench, where the Pacific Plate is subducted to the west under the Australian Plate.
The US Geological Survey has determined that the earthquake was due to northeast to southwest tension, with the earth being stretched rather than compressed. This leads to faulting that is oriented southeast to northwest, with vertical motion that will deform (and possibly rupture) the sea-floor, producing a tsunami.
This earthquake mechanism suggests that the earthquake was not precisely along the plate boundary, but was within the Pacific Plate where it has been bent over to the west and southwest as it enters the subduction zone.
The mechanism and the aftershock distribution suggest that the earthquake rupture propagated from the epicentre at the southeast towards the northwest, and not to the south on the much longer and larger Tonga-Kermadec Trench. Beyond the rupture, the plate boundary then gradually turns to the west and passes north of Fiji.
The orientation of the faulting would have generated a tsunami with higher waves to the northeast (towards Samoa) and to the southwest (towards Tonga, eastern Fiji, and beyond towards New Zealand and the Tasman Sea). This may well have seriously affected communities on isolated islands, especially in Tonga and Fiji. Hopefully, authorities will be urgently contacting these people.”
Nora Welch is theTusnami Gauge Operations Manager at GNS Science, the Institute of Geological and Nuclear Sciences in New Zealand (courtesy of the New Zealand Science Media Centre).
“I received a text on my cellphone at about 7am from the USGS advising the magnitude, location, and depth of the earthquake. We were in tsunami mode from then on. During my drive to work, I discussed the quake and its possible implications with a colleague.
On arrival at work I found our tsunami modelling group were working out preliminary wave heights and arrival times around the New Zealand coast. I joined a group watching live data from our tsunami gauges on the large screen for the first signs of waves to arrive. The gauges are connected by either satellite or radio links and we receive the data in real time. It was arguably the first real test for the tsunami gauge network we have been gradually installing for the past 18 months. The systems worked well.
Throughout the morning we were in regular contact with Civil Defence officials in Wellington providing updated information. We stressed that the first wave is not necessarily the largest wave. We also emphasised that as well as larger than normal waves, there was a possibility of strong currents at many coastal locations.”
Dr Huilin Xing is from the Earth System Science Computational Centre at The University of Queensland
“The tsunami warning system workedand is very helpful.But the problem is that there were a lot of false alarms, because not all large earthquakes can generate a tsunami.From research we know we can expect that if an earthquake is larger than magnitude 6.5 there may be a tsunami, but this is not directly or linearly related to size. This means we really need to keep looking deeper to work out what kinds of earthquakes can generate tsunamis and how big the tsunami might be. This is the most difficult part sinceone needs to know details of both the earthquake itself (i.e. depthand focal mechanism) and its triggered sea floor motion and interaction withwater. Currentlyno single model can modelthe whole process of an earthquake andits triggered tsunami generation.
From the recent earthquakes, the eastern Australian coast may be in a high risk area in the near future.”
Associate Professor Robert Heath is a crisis management expert at the University of South Australia.
“The earthquake was between a 7.8 and 8.3. Media reports are saying 8.3 but I think it will be downgraded to around a 7.9. It was within the island group area and of course you are not only talking Western Samoa and American Samoa but you are talking about the Cook Islands at one extreme and Fiji at the other extreme. All of them will have some effects from the tsunami.
You don’t get tsunamis unless the earthquake occurs out at sea and it needs to be of a magnitude of around about a 7 or a 7.5. It also needs to have a large volume of uplift or a down lift. In other words classically what you need is several billion tonnes of rock and mud moving so that you can create that sort of uplift swell.
This tsunami appears to have been localised. You can get tsunamis very close on shore, from smaller sized earthquakes like in Japan, simply because the disturbance happens close to the shore. They were expecting a 2 metre tsunami in NZ but the first reports as it came onto the NZ territorial waters were of around 40cm which is still a significant disturbance but this tells us the earthquake was of a small area in terms of its size.
There are going to be more fatalities and casualties unfortunately. What you have is large group of islands some of which are relatively remotely connected. Those closest to the epicentre, if the early reports of around a 3 metre high wave are correct, would have experienced quite a bit of inundation. There are at least two villages that have been levelled.
One of the things we know about causalities/ death tolls from tsunami type events is that the numbers start off slow then you get overbuild – that is we over report, then the figures come down again as people straggle back and report in. It will be quite a while before we know in better than rough figures what has happened.
There may well have been some minor tsunami impacts on the Australian sea board. They really weren’t giving us a tsunami alert on this occasion but historically we have had tsunami effects from as far away as an earthquake off the South American continent – that was a huge one more like the south east Asian tsunami event from a few years ago, but we did lose some people even in Morton Bay in Queensland. So be aware we can get some impact from these types of events even though the northern part of Australia is sheltered by our reef. In Australia the continental shelf also reduces the size of the impact because it is a couple of hundred metres out to sea, so when a tsunami builds up it is still a couple of hundred kilometres off shore and will inevitably lose some of its size by the time it reaches us.
Prehistorically we have had some huge tsunami impacts on our coast line with boulders found a few hundred metres about sea level which probably came from when half an island fell apart in the Hawaiian chain. Mega tsunami’s, like mega bushfires, don’t happen often but they can happen to anyone.”
Dr Ray Canterford is Head of the Joint Australian Tsunami Warning Centre at the Bureau of Meteorology. To organise an interview with Dr Canterford please contact David Grant (Tel: 03 9669 4057; Mob:0439 452 424).
“This morning’s tsunami is a reminder of the terrible force that can be unleashed by earthquakes under the sea.
Australia has a robust warning system in place – including tsunami “no threat”, “marine warnings” and “land inundation warnings.” Fortunately for Australia the Joint Australian Tsunami Warning Centre was able to issue a “no threat” quickly after the event. However, it has had a devastating impact on Samoa.”
Associate Professor Dale Dominey-Howes is Co-Director of the Australian Tsunami Research Centre and Natural Hazards Research Laboratory at the University of New South Wales (www.nhrl.unsw.edu.au)
“Today’s earthquake-tsunami event has been locally devastating. Reports show the earthquake was large (approx magnitude 8), was widely felt in Samoa and triggered a ‘regional’ tsunami that affected Samoa and American Samoa. Locally the tsunami may have had waves in excess of 3 metres high and appears to have flooded inland to considerable distances where the coast is low-lying.
The tsunami impacted the northeast coast of New Zealand but was less than 1 metre high. The Pacific Tsunami Warning System issued a regional warning for the affected areas and accurately predicted arrival times at various locations. Unconfirmed reports suggest that in some places people recognised the natural warning signs for the tsunami and evacuated to higher ground. In other areas this does not seem to have happened. Media reports and communication with people in the affected areas confirm a slowly rising death toll. Events like this have occurred in this region before and are not entirely unexpected.”
Dr Dale Dominey Howes can be contacted on his mobile – 0401 647 959
UK Science Media Centre Round-up
Professor Bill McGuire, Professor of Geophysical & Climate Hazards and Director of the Aon Benfield UCL Hazard Research Centre, UK, said:
“This most recent tsunami disaster shows that there are lessons we yet need to learn from 2004. Most critically, populations living close to faults capable of producing earthquakes that trigger tsunamis must be taught to self-evacuate when the ground shakes or the sea recedes. Waiting for a warning from a central monitoring station could mean the difference between life and death”