Tsunami recorded in NZ; NIWA predictions prove correct

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Parts of the West Coast of the South Island received a tsunami wave over one metre high as a result of the Gizo (Solomon Islands) tsunami.

Official sea-level gauge results from NIWA show the highest wave height of 1.1 metres occurred at Charleston, near Westport at 20:10 on Monday 2 April (NZST). "Fortunately, this wave occurred around mid-tide on the West Coast," says Dr Rob Bell of the National Institute of Water & Atmospheric Research (NIWA).

Well over a year ago NIWA recognised the possibility of the Solomon Islands as a possible northern source for substantial tsunamis along the west coast of New Zealand. As part of a consultancy project for several regional councils, NIWA scientists, using their RiCOM model, looked at a variety of tsunami scenarios based upon large magnitude earthquakes from the same area where the latest earthquake occurred.

NIWA’s computer model predictions of wave height, areas most likely to record the largest waves, and arrival times, matched very well with what actually happened with the Gizo tsunami. The model predicted that the West Coast around Westport was likely to get the highest waves; and the modelled arrival times – at least one hour later than projected by the Pacific Tsunami Warning Centre warning bulletin – were correct. On Monday (2 April), NIWA scientists kept in close contact with the Ministry of Civil Defence & Emergency Management, and other experts, to ensure the model predictions were clearly communicated.

Tsunami Observations in New Zealand Gizo(Solomon Islands), Magnitude 8.1, 20:40 UTC April, 2007 (08:40 2nd April NZST)

Tide Gauge Lat(N) Long(E) Arrival Time 2 Apr (NZST) Arrival Time 2 Apr (UTC) Periods of waves(min) Max wave height above mean level(cm) Max peak–to–trough wave height(cm) Time of peak wave height(NZST) Time of peak wave height(UTC)
Charleston –41.908 171.433 17:21 5:21 6’–8’ on top of larger 28’–32’ 51 110 20:10 2 Apr 08:10 2 Apr
Jackson Bay(NTF–BoM) –43.957 168.616 16:52 4:52 7’–11’ on top of larger 27’–32’ 38 84 19:55 2 Apr 07:55 2 Apr
New Plymouth (Port Taranaki) –39.055 174.033 17:10 5:10 10’–14’ on top of larger 22’–24’ 33 60 19:50 2 Apr 07:50 2 Apr
Little Kaiteriteri(Tasman DC) –41.048 173.027 18:37 6:37 11’–13’ & 30’ 18 31 21:57 2 Apr 09:57 2 Apr
Kapiti Is. –40.842 174.938 18:53 6:53 19’ 21 30 00:38 3 Apr 12:38 2 Apr
Anawhata –36.921 174.461 16:40 4:40 30’–40’ 12 20 17:20 2 Apr 05:20 2 Apr
Kaingaroa, Chatham Is. –43.732 183.733 18:20 6:20 10’–11’ 10 20 18:40 2 Apr 06:40 2 Apr
Sumner Head –43.570 172.773 20:50 8:50 15’–18’ & 22’–30’ 7 12 02:22 3 Apr 14:22 2 Apr
Kaikoura –42.415 173.703 20:38 8:38 12’–14’ 7 12 02:18 3 Apr 14:18 2 Apr

Acknowledgement:

Sea–level gauge data supplied by National tidal Facility (Bureau of Meteorology) for Jackson Bay, Port Taranaki Ltd. for New Plymonth, Tasman District Council for Little kateriteri and NIWA for other sites.

Background:

NIWA coordinates a network of 20 open coast sea-level recorders around New Zealand, including the Chatham Islands, and Antarctica (Scott Base). The recorders collect accurate measurements of sea level and tides for monitoring coastal hazards such as storm surge and tsunami, and studying longer-term coastal processes, including El Niño effects and sea-level rise. Data are uploaded nightly and some sites are displayed at www.niwascience.co.nz/services/sealevels. The data are also used for processing hydrographic surveys of the seabed topography and field monitoring of invasive species such as mosquitos at the high water mark.

Some of the recorders have been tsunami-enabled to store sea-level measurements quickly at 1–minute intervals to better describe the various waves that make up a tsunami event. Currently, any emergency response in detecting and confirming a tsunami is undertaken on a best-endeavours basis with the Ministry of Civil Defence & Emergency Management. NIWA is currently assisting Land Information New Zealand to develop a round-the-clock sea-level service as part of a new national tsunami early-warning system.

The present network is supported by several regional councils (Environment Canterbury, Northland Regional Council, Auckland Regional Council, Environment Waikato, Hawke’s Bay Regional Council, Otago Regional Council, Environment Southland), port companies (Westgate, Primeport-Timaru, Lyttelton), territorial authorities (Tasman District Council), Antarctica NZ, and Australia’s National Tidal Centre.

Gizo (Solomon Islands) tsunami: Mw 8.1 2040 UTC 1–Apr–2007 New Zealand sea-level gauges on west coast.

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