International expert outlines risk to Pauanui and Tairua of tsunami

An international expert who has spent 20 years studying tsunamis is among the team of professionals studying what Tairua and Pauanui can expect if a '2011 Japan-like' tsunami was to hit the Coromandel.

Dr Jose Borrero has presented the Tairua-Pauanui Tsunami Working Group and Tairua-Pauanui Community Board with extensive modelling scenarios based on historical information, recent studies, data from major events around the Pacific and eye witness reports from previous tsunamis in New Zealand and internationally to show what can be expected.

It shows:
• A fault line known as the Tonga-Kermadec Subduction Zone, lies off the east coast of the Coromandel and extends from Gisborne northward to Samoa. This type of fault, which is a major boundary between two of the earth’s tectonic plates, is known to produce large earthquakes and tsunamis.

• Its proximity to the Peninsula means an earthquake centred along the fault would give people in coastal towns like Whitianga, Tairua and Pauanui less than an hour to get to higher ground or go as far inland as possible before the tsunami wave would arrive, with the peak of the wave occuring approximately 1 hr and 15 minutes after the earthquake.

• The warning signs of such an event would be the earthquake itself, which would likely be felt widely around the region with strong shaking lasting for 30 seconds or more. If the earthquake was not warning enough, other warning signs of an impending tsunami include unusual tidal movements such as the rapid withdrawal of the water or a loud roaring noise like a jet engine coming from the sea.

Dr Berrero says the Pacific has several 'subduction zones'. These are areas in the earth's crust where one plate dives under another plate before it then 'snaps', generating waves.

"The one we're worried about is the Kermadec Trench," he said.

He said although the magnitude of an earthquake is important, of more concern is the location of the rupture on the faultline. For this reason the board was presented with different maps highlighting the inundation caused depending on the magnitude and location of the rupture on the Kermadec fault.

The worst case scenario - a magnitude 9.3 with a 3.5m slip on southern segments of the Kermadec trench - caused inundation of between 2m and 6.1m over large parts of Pauanui from the beachfront back, and at Tairua north beach, Hemi Pl, the esplanade along Paku Bay and into Manaia Rd, Hornsea Rd, parts of Ocean Beach Rd and Tairua Main Rd.

These maps will be available to view at two community open days on Auckland Anniversay Weekend (January 25 in Pauanui and January 26 in Tairua 10am - 3pm both days) where staff can fully explain the circumstances in which this scenario might eventuate.

The open days will be held at the Pauanui Fire Station meeting room on Saturday January 25 and at the Tairua Rugby and Sports Club on Sunday January 26. All are welcome to come and view the latest scientific modelling on display and talk to members of our Tsunami Action Working Group (see story below).

Tsunami Action Working Group established
A tsunami action working group has been established to carry out the critical next stages in this work including a public information campaign to educate people on the risks and what to do in a tsunami.

Lynette Dey, Tairua Information Centre Manager, is appointed Working Group Chair.

This group of community representatives is now preparing for open days in Tairua and Pauanui (on Auckland Anniversary Weekend January 25 and 26) to present information on tsunami risk and raise awareness and discuss options for minimising risk.

To find out more, sign up for our South East area e-newsletters (to the left of this article) and encourage others to do so.

Some of the longer term considerations are land use planning so that residential care homes and kindergartens for example may not be established in higher risk areas.

A risk management strategy will be developed following feedback from the community open days and will be presented to the Community Board.

Tsunami sirens still useful but don't rely on them
TCDC and WRC have lobbied for a long, continuous tsunami siren that is the same for all communities.

Civil Defence Emergency Manager Gary Talbot says the meetings have been held with representatives of all Coromandel communities and there is still widespread support for tsunami sirens even though there's international research that does not favour their use.

"The key message for communities is that if the ground shakes, move immediately to higher ground.

"Organisations must have their own well-practised evacuation plan and householders need to know who you are dependent on and who is dependent on you," says Gary. "Sirens are not the answer."

As was outlined in Dr Borrero's presentation, so-called far-field or distant tsunami do not pose a largescale land inundation hazard for Tairua and Pauanui although it's important to stay away from the water due to strong currents arriving much later than with near-distance tsunami.

"An issue with far-field events are the strong and potentially damaging currents that can happen as much as 6 to 20 hours after the tsunami arrives,” says Dr Borrero."

ENDS

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