Several dozen people are dead in the Samoan islands following a magnitude 8.3 earthquake this morning that was centred 205 km south of the Samoan capital, Apia.
Samoa’s disaster management office has said that as many as 100 people have been killed, and more injured. The tsunami warning in New Zealand was downgraded to a tsunami alert and while Geonet reported that in Northland, the East Coast of the North Island and in the Chatham Islands, wave run-ups up to one metre along the coast were possible, the first waves were seen to be 40cm in height.
The Joint Australian Tsunami Warning Centre issued a release saying that tsunamis would not affect Australia.
The NZ SMC and AusSMC rounded up these comments from experts:
Nora Welch, Tsunami Gauge Operations Manager at GNS Science, comments:
“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.
“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 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 Ray Canterford, Head of the Joint Australian Tsunami Warning Centre at the Bureau of Meteorology, comments:
“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, Co-Director of the Australian Tsunami Research Centre and Natural Hazards Research Laboratory at the University of New South Wales, comments:
“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 Huilin Xing is from the Earth System Science Computational Centre at The University of Queensland comments:
“The tsunami warning system worked and 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 since one needs to know details of both the earthquake itself (i.e. depth and focal mechanism) and its triggered sea floor motion and interaction with water. Currently no single model can model the whole process of an earthquake and its 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, comments:
“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.”