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Tsunami risk and preparedness in New Zealand

Backgrounder to the Tsunami reports
In January 2005, in response to the Boxing Day tsunami in the Indian Ocean, the Government asked for more information on the risk of tsunami for New Zealand and our preparedness to deal with them. A team of specialists was contracted to review existing information on tsunami in New Zealand. The team modelled this information to give an overview of the tsunami hazard and two tsunami reports were produced by GNS Science. The reports are:

  • A Hazard and Risk Report, which provides a synthesis of the current knowledge on the tsunami hazard in New Zealand and the risks of tsunami to New Zealand communities; and
  • A Preparedness Report, which reviews New Zealand’s level of preparedness at the national and regional level for the tsunami hazards identified in the Hazard and Risk Report.
Tsunami are generally caused by seafloor earthquakes and are a series of waves that surge inland. Whether or not a tsunami is generated, and how big it is, depends on a range of conditions, such as the type and size of the earthquake, its depth and location. The historical incidence in New Zealand of damaging tsunami is low. However, the potential tsunami risk for coastal communities in vulnerable areas is significantly greater than previously understood.

The Reports
The Hazard and Risk Report estimates the level of tsunami risk for 19 coastal localities in New Zealand – Whangarei, North Shore, Waitakere, Auckland, Manukau, Tauranga, Whakatane, New Plymouth, Gisborne, Napier/Hastings, Kapiti, Porirua, Lower Hutt, Wellington, Nelson, Christchurch, Dunedin, Timaru and Invercargill.

In general terms, the tsunami risk is similar to New Zealand’s earthquake risk. The Hazard and Risk Report estimates potential losses in terms of possible lives lost, injuries caused and the cost of building damage. The potential for loss of life is presented on the basis of there being no warning of the arrival of a tsunami. However, effective warning and good public education can substantially reduce the potential loss of life. The modelled median estimate of damage to property from a tsunami is approximately twice that of an earthquake of a similar return period. The return period is the average interval between which the event may occur. There is wide variability in these loss estimates because of uncertainties in the modelling process.

For example, the modelled potential loss of life for a 500 year event in the Auckland region was 122 but could range between 24 and 519. For Christchurch the figure was 280 but could range 60 and 1,500. For Napier Hastings the figure was 320 but could range between 69 and 1,300. All of these figures are modelled on a "no warning" basis to allow regional comparisons of risk. With effective warning and response arrangements in place these potential losses could be reduced by 90-95%.

Types of tsunami
There are three main categories of tsunami to consider when addressing monitoring and alert arrangements for warning of tsunami. These are:
  • distant source tsunami with three to twelve hours travel time to the New Zealand coast;
  • regional source tsunami with one to three hours travel time to the New Zealand coast; and
  • local source tsunami with less than one hour travel time to the New Zealand coast.
The most likely source of a tsunami, whether distant, regional or local, will strongly influence the types of precautions a community needs to take. The ability to warn and evacuate vulnerable coastal communities in the event of a tsunami varies widely from region to region. For distant source tsunami the timeframe available is generally sufficient to provide a reasonable level of warning to allow people at risk to move to safety.

New Zealand receives alerts of distant source tsunami from the Pacific Tsunami Warning Centre in Hawaii. However, the Pacific Tsunami Warning Centre does not provide warning of tsunami from the South West Pacific, the Southern Ocean or close to New Zealand waters. New Zealand has not yet developed the capability to monitor for regional source tsunami. Capacity to receive alerts and communicate a warning for regional source tsunami is also undeveloped.

New Zealand has initiatives in place to provide improved alerts of distant source tsunami, and to create the ability to alert for regional source tsunami. This involves upgrading some sea level gauges so they can detect tsunami. It also involves GeoNet, the system for monitoring for seismic hazards such as earthquakes, which has the potential to provide alerts of distant and regional source tsunami. There are no arrangements in place to monitor for local source tsunami. Currently there is little practical warning possible for the arrival of a local source tsunami. Public education encouraging people to recognise and respond to potential natural triggers (such as an earthquake or the sea receding) is the principal protection.

Next Steps
The government will consider improvements to the modelling completed for the two tsunami reports, as recommended in the Hazard and Risk Report. It will also consider improving preparedness arrangements, as recommended in the Preparedness Report. Civil Defence and Emergency Management (CDEM) groups need to be involved in consideration of many of these issues. CDEM groups are regionally-based consortia of local authorities working in partnership with emergency services (police, fire, health), lifeline utilities (electricity, gas, telecommunications) and others to deliver emergency management within regional boundaries. CDEM groups have the local knowledge to assess the implications of the two tsunami reports for their regions both in terms of the level of tsunami risk and the right mix of preparedness arrangements for the kinds of risks each region faces.

The two reports listed below are available as full printable documents or broken into their sections

Review of Tsunami Hazard and Risk in New Zealand:
For a full printable version (pdf) of this document:

Review of New Zealand's preparedness tsunami hazard, comparison to risk and recommendations for treatment:
For a full printable version (pdf) of this document:
Images and related documents
Tsunami Travel Times (jpg 1,173kB)
500 Year Tsunami map (jpg 270kB)
Tsunami Signage: 2007 GNS Science report and recommendations (pdf 2.0MB)
Tsunami Signage: Technical Standard (pdf 700kB)