Tsunami Hazard to Coastal Populations

Reduce your personal risk (created by Michael Paine, May 2008)

Be alert and prepared - not alarmed. This is a low-probability, high-consequence event that calls for a little preparation in case a warning is issued. These are similar to the things that people do to prepare for cyclone warnings in tropic areas and bushfires. The following advice applies mainly where there is no local tsunami action plan.

Although the likelihood of a mega-tsunami is low there are some simple things you can do to significantly reduce the risk of fatality:

Identify if you live, work or play in a vulnerable location - find out the approximate height above mean sea level. As a rough guide coastal and estuary land less than 10 metres above mean sea level is "at risk" and 5m or less should be considered "vulnerable". Google Maps has a sea level rise add-on (update: no longer available - try this tips page or Sea Level Rise Explorer) that can give a very rough guide (detailed modelling is needed to assess vulnerability as there are many factors that influence tsunami inundation). The following links are to JPG screen snapshots from Google Maps in 2008 - red shows 5m contour and yellow shows 10m contour: - Narrabeen, Manly, Sydney , Brisbane, Gold Coast, Sunshine Coast, Nowra, Wollongong, Gosford, Newcastle and Forster (Update Dec09: There are more accurate maps being developed by SES organisations and this page will link to them when they are published on the internet or try Sea Level Rise Explorer). Update June 2016: NSW SES now has similar maps online.
Identify a safe location to go to in the event of a tsunami warning - a nearby hill or headland or at least the third storey of a reinforced concrete building
Plan an evacuation route by foot to reach that safe location (avoid the need for driving a car because the roads will likely gridlock)
Subscribe to the email or RSS warning service of the US Pacific Tsunami Warning Center
Subscribe to a mobile phone alert service like the Australian Early Warning Network which offers a free SMS service that relays tsunami warnings issued by the Australian Bureau of Meteorology. The service also covers other risks such as bushfires and cyclones. SMS-Tsunami-warning.com is a similar international service. With hundreds of thousands of people potentially afffected, you may not be able to rely on the Internet, landline telephones or mobile phones at the height of a tsunami emergency so have a portable radio available for receiving updates.
If you receive a tsunami warning that is relevant to your location, or feel an earthquake, quickly get your evacuation plan into action. If a mega-tsunami does inundate the area do not return to low-lying land until given the all-clear by emergency services as other waves are likely to follow after the first wave and each wave can last for 20 to 30 minutes. The danger may last for many hours and possibly more than 24 hours.
Approach your local council and politicians and ask to support (ie fund) State SES to develop tsunami warning action plans and infrastructure (such as a public address system) and to have inundation modelling carried out. See the [NSW] State Tsunami Plan( pdf 2311kb) - issued in 2005. See Tsunami Notification Zones for British Columbia as an example.
Most importantly, relax and enjoy living near the ocean, knowing that you have made basic preparations for a worst case scenario

Update Nov09: Brochure "Tsunami Survival Guide" based on the above tips ""If you are at the beach and feel an earthquake – GO TO HIGH GROUND" - don't wait for a tsunami warning signal because the tsunami could arrive in less than 30 minutes (advice from Tsunami expert Dr Charles Mader)

Update Jun17: Magnitude 5 quake causes an undersea landslide tsunami in Greenland. USGS info.

Tips from a tsunami survivor

These tips are from Kristin Fedorow, an Australian who survived the 2004 tsunami on the Thai coast:

1) Tsunamis usually have more than one wave
2) The later waves are usually much bigger
3) The water does not necessarily recede before the wave approaches
4) The wave does not necessarily look big as it comes in
5) The time between waves can be much longer than a few minutes

These points are illustrated in this Youtube video: Japanese mega-tsunami in 2011
and this confronting movie about the 2004 tsunami: The Impossible.

Slide show presentation on the tsunami hazard to Sydney (by Michael Paine at a Friends of Narrabeen Lagoon Catchment meeting, March 2008)

Includes recent computer modelling of a mega-tsunami from the Tongan Trench that has similar features to the 2004 Indian Ocean Tsunami.

12Mb Quicktime presentation + Youtube version
3Mb PDF of the presentation
Notes for simulation of an Magnitude 9 earthquake at the Tonga Trench by Dr Charles Mader (from the DVD with his text book Numerical Modeling of Water Waves). The chances of such an extraordinary but deadly event are unknown at this stage (however, a magnitude 7.9 earthquake occurred near Tonga in 2006 and a Magnitude earthquake 8.1 occurred south of New Zealand 3 days before the 2004 Indian Ocean event. Update: 8.3 quake near Tonga on 30 Sep 09). The Mader modelling was based on the actual tectonic movements for the Sumartran earthquake that caused the 2004 Indian Ocean tsunami (Aug08: assumption independently confirmed). Others have noted that the Tongan Trench is the fastest known subduction zone. The resulting tsunami is particularly devastating for the East Coast of Australia, with a predicted height of around 10m (the deep water wave height would be less than that modelled due to dispersion but the shallow water amplification would counteract this effect meaning a likely 10m runup along many coastlines). Apr 11 New Scientist: Japan disaster suggests that Tonga is not immune to a Magintude 9 earthquake.
It has been estimated that 330,000 people live within the 10m elevation zone along the coast (and many estuaries) of New South Wales. Adding the Queensland Coast the population at risk is likely around half a million - something that deserves urgent attention.
Recent Geosciences Australia modelling indicates that a Magnitude 8.5 earthquake in the Tonga region is unlikely to pose a major mega-tsunami threat to the Australian coast - which is good news. The Magnitude 9 quake modelled by Dr Mader much larger and much less likely to happen in our lifetimes. More about the risk to Australia.
19 Aug 14 Scientific American: Big Earthquake Looms for Chile - a long way from Australia but a potential tsunami threat. This Wikipedia page has info about the 8.2 magnitude 2014 Iquique earthquake that generated a 2.1m local (Chile) tsunami. Travel time to the Australian East Coast was 17 hours but the tsunami height was negligible. However an 8.5 magnitude earthquake near Peru in 1960 generated a small tsunami in Sydney and the largest tsunami in Hawaiian history - see the lecture by Charles Mader SWModel1.mp4 (download from here) at around 24 minutes into the talk. Also New Scientist: Chile is facing yet another massive earthquake "Fortunately Chile has good systems for responding to earthquakes... It holds major evacuation drills involving thousands of people. In coastal regions, evacuation sirens warn of impending tsunamis, and alerts are sent to cellphones and through Twitter." + Why the [2010] Chile quake tsunami was smaller than feared
28 Aug 14 Uni Queensland: South east Australia most prone to tsunami threats along eastern coast.
Reducing The Death Toll From Tsunami (written a fortnight after the Indian Ocean disaster)
15 Aug 08 Breakthrough! Illawara Mercury: Tsunami a real threat to Illawarra: professor - a tsunami education and evacuation plan for Illawarra would be released in November.
19 Apr 09 - Tasmanians becoming prepared.
1 Oct 09 ABC: 'No agreement' on [Australian] tsunami alert system - Emergency services experts say Australia's tsunami warning procedure is still lacking an effective alert system [following the Samoan tsunami].
1 Sep 14 Cahill Expressway interpretive display: The Great Eel at Boora Birra [an aboriginal account of the creation of some of Sydney Harbour, according to F. Bodkin, 2001]: ...The Earth began to shake violently, and a great chasm opened up in the ground, following the fleeing lawless ones and swallowing them as they fled towards the flatlands. Then a storm came in from the sea, and the waves crashed across the flatlands until they reached the cliffs that marked the beginning of the highlands. [this could well be a description of mega-tsunami, such as the one that probably arose from the Bulli Slide a few hundred years ago]
25 May 2015 New Scientist: New Zealand's worst earthquake fear confirmed by sediment survey - evidence of a huge megathrust earthquake crossing segment boundaries there some 500 years ago [source of the mega-tsunami on the east coast of Australia?] BSSA Abstract.

Update 2008

Geoscience Australia tsunami page with a brochure link. Opinion: the tsunami hazard to the east coast appears to be under-rated.
Echoes of ancient tsunamis (2006) Along the eastern Australian coastline, where most Australians live, the tsunami threat comes from several sources. Although they have produced few historical tsunamis, the Solomons trench, the New Hebrides trench off Vanuatu, the Tonga–Kermadec trench north of New Zealand, the Alpine fault in New Zealand and the Puysegur trench south of New Zealand may all have the potential to produce earthquake-generated tsunamis capable of reaching Australian shores. More work needs to be done to characterise the earthquake mechanisms in these regions... The steep slopes of the continental shelf on the eastern Australian margin may induce underwater landslides capable of producing localised tsunamis...
The Joint Australian Tsunami Warning Centre - The establishment of the fully functional Australian Tsunami Warning System is a four-year project funded by the Federal Government that is due to be completed in June 2009. At the completion of the project Australia will have considerably improved earthquake and tsunami detection equipment in Australia and around the region, enhanced scientific modelling of tsunami, a responsive warning system, and increased public awareness and community preparedness.
EMA: Australian Tsunami Alert System
Tsunami warning system will 'stop false alarms'
Science of Tsunami Hazards: TSUNAMI SCENARIO SIMULATOR: A TOOL FOR ENSURING EFFECTIVE DISASTER MANAGEMENT AND COASTAL EVACUATION IN A MULTILANGUAGE SOCIETY + TSUNAMI PUBLIC AWARENESS AND ITS ROLE IN RISK EDUCATION "The 2004 Indian Ocean tsunami has demonstrated that large magnitude, destructive tsunami occur in areas close to Australia. The commitment by the Australian Federal Government to the development and installation of an Australian Tsunami Warning System is a vital element in helping to keep Australian coastal communities and public and private infrastructure and assets safe from tsunami. However, the physical components of the warning system are only one element of making Australia safe. The other, perhaps more important element, is preparedness and response. Emergency Management Australia and the State Emergency Services are the agencies tasked with the responsibility of evacuating coastal communities if required. The success or otherwise of public response to tsunami warnings will be dependent on their understanding of tsunami hazard and risk. We provide selected results from a pilot investigation into public awareness of tsunami risk in the Sydney region – a fundamental necessity for developing appropriate risk mitigation strategies. Our questionnaire survey of members of the general public and coastal council professional officers indicates that little has been learned since the December 2004 Indian Ocean tsunami disaster. This presentation provides a summary of what the public knows and importantly, does not know with respect to tsunami. We make a series of recommendations to assist responsible organisations in thinking about risk mitigation."
28 Aug 08 A survivor of the Indian Ocean Tsunami started a Facebook page to raise awareness of the risk (page removed in 2016 - beware of false identities)
May 08: Taking a punch: Building a more resilient Australia - report "We need greater clarity on the precise management and coordination arrangements in the case, for example, of a devastating tsunami impacting on southeast Australia...The Commonwealth agency seen to be responsible for this, Emergency Management Australia (EMA), has no mandate, legislation or Cabinet endorsement with which to take command. The delivery of EMA functions for the most part is the result of goodwill on behalf of other agencies. This is clearly not a satisfactory situation." "A $70 million early warning system is being set up to record any earthquakes that could trigger giant waves to strike the NSW coast but it’s not clear how communities get informed, particularly if a night-time incident occurred..."
Why weren't we warned? Fiction to raise awareness
The Australian Tsunami Warning System and lessons from the 2 April 2007 Solomon Islands tsunami alert in Australia - Dale Dominey-Howes, UNSW & others "This has taught us two important lessons. First, the physical warning system is not enough in itself to result in a reduction of vulnerability to tsunami. Just because we have a warning system does not mean the job is done. Second, much work needs to be undertaken to ensure that communities have been educated about tsunami hazard and risk and what alert and warning messages mean, how to react, where to evacuate and how quickly to respond. Furthermore, the emergency services and the Emergency Management Australia must work urgently to effect community tsunami disaster management planning, identiﬁcation of safe evacuation zones, testing and evaluation of tsunami warning messages and trialing of these plans with the public." + Geological and historical records of tsunami in Australia (abstract) + Tsunami and palaeotsunami depositional signatures and their potential value in understanding the late-Holocene tsunami record (abstract "we are unable to replicate the previously reported findings of tsunami deposits...") + Tsunami risk mitigation and the issue of public awareness
Emergency management of tsunami in New South Wales and the response to the Solomon Islands tsunami April 2nd 2007 - Australian Journal of Emergency Management

Update July 2006 with advice from EMA (see also Australian news)

Key points (thanks Mark Sullivan, Director Capability Development EMA):

EMA is working with States and Territories and relevant industry, education, volunteer and community sectors to enhance community preparedness through awareness raising, education and training.
Over four years, from July 2005 to June 2009, the Bureau of Meteorology, Geoscience Australia (GA) and Emergency Management Australia (EMA) will implement a comprehensive end-to-end Australian Tsunami Warning System (ATWS). The ATWS will be delivered through enhancements to the existing Australian Tsunami Alert Service (ATAS), and will comprise upgraded seismic and sea level monitoring networks, computer modelling of tsunami propagation to aid impact forecasting, and national awareness raising and capacity building initiatives. The ATWS, once fully operational, will deliver timely and accurate warnings to the Australian community in such a way as to elicit an appropriate response from those at risk.
By 2007 estimates will have been made of the credible limit of offshore tsunami wave height for the entire Australian coastline.
Inundation modelling is being undertaken for some West Australian coastal communities
Australian Emergency Management Committee's Tsunami Working Group will meet in September 2006 with a view to agreeing on a national strategy for awareness raising and capacity building. Some local jurisdictions have already developed hazard specific arrangements for tsunami, and EMA is committed to working with all jurisdictions to enhance these already existing arrangements to effectively respond to a rapid onset event such as tsunami, including the eduction sector.
Communities and key stakeholders have been, and continue to be, engaged; and a national picture of tsunami risk is being developed. In the very near future, the Australian community can expect to be provided greater access to relevant
awareness material, and those with key responsibilities will further benefit from tailored education, training and exercising. On this basis, the Australian community will come ever closer to being a 'Tsunami Aware Community', and thus be better prepared to respond appropriately to signs of tsunami in Australia and overseas, as well as respond in a timely and appropriate way to ATWS warnings.

Related links

Australian Emergency Manuals

Australian Journal of Emergency Management:

Observations on Tsunami disaster in Papua New Guinea - 1998
After the Wave: A wake up warning for Australian coastal locations King and Gurtner consider Australia’s vulnerability to tsunamis and storm surges...The increasing emphasis on disaster reduction through mitigation
and preparedness has put greater responsibility on local government and relevant authorities to ensure
that such lessons are understood and used to mitigate future contingencies. The tsunami is a warning that
reinforces current mitigation efforts, and in particular, the long-term goals of education and the planning
of coastal land use.
Tsunami risk mitigation and the issue of public awareness (PDF) - Is Sydney at risk from tsunami
flooding and if so, from where? Approximately 330,000 people in New South Wales live within 1km of the ocean or a coastal river and at an elevation of no more than +10 metres above sea level (Molino Stewart, 2005). These people, their homes,
businesses and all infrastructure are vulnerable to the effects of tsunami inundation...
Managing tsunami risk in coastal communities: identifying predictors of preparedness.
Early warning systems: reframing the discussion - The emphasis on early warning systems has turned attention and funding to the current capabilities and developments in science and technology, and unfortunately, distracted us from the central issue of addressing the real needs of the communities and people at risk.