Science & Environment

Japan tsunami touches New Zealand

Tsunami waves triggered by Japan's Magnitude 9.0 quake touched all of New Zealand's coasts, scientists report.

A 86cm wave was recorded in the port of Lyttelton, the NZ township closest to the epicentre of the country's own catastrophic 6.3 tremor in February.

And a gauge at Scott Base, in Antarctica, even registered a 10cm wave, says the National Institute of Water and Atmospheric Research (NIWA).

NZ is some 8,000km from Japan. The first waves arrived in about 12 hours.

The biggest were seen in Whitianga, in North Island, and Kaingaroa, on the Chatham Islands east of the NZ mainland, where heights (from crest to the trough) of 1.6m were measured.

Mount Maunganui (on the northern coast of North Island), and Charleston (on the west coast of South Island), and Timaru (on the east coast of South Island) also recorded wave heights over a metre.

At the majority of the 19 sea-level gauges monitored, the biggest waves did not arrive for many hours after the instruments started registering changes from normal tide readings.

At Timaru, the largest wave height did not occur until more than 40 hours after the first wave hit, the institute said.

This delay was probably due to waves bouncing off continental shelves all around the Pacific including South America and local coastal headlands and offshore ridges, it explained.

Image caption US scientists estimated 11 March tsunami progression over the entire Pacific basin

"It's important to understand that tsunami waves can continue for some time after the first few waves hit," added NIWA Principal Scientist, Dr Rob Bell.

"It's not safe to assume that once you have seen one wave, the risk subsides and all returns quickly to normal.

"We are still recording obvious wave heights at our sea-level gauges now, days after the earthquake, which are affecting currents in harbours and estuaries.

"The size and timing of the waves recorded by the sea-level gauges are very similar to those estimated in the response phase of this event.

"The accuracy of this information is vital for civil defence and emergency management when they are making decisions about tsunami warnings, to ensure the hazardous impacts of a tsunami event in New Zealand are minimised."

More than 160 people were killed in the M 6.3 quake that struck the Christchurch area on 22 February.

A national memorial day on 18 March will feature events planned in the city's Hagley Park. The UK's Prince William will also tour devastated areas.

Quake recovery efforts are expected to cost New Zealand at least NZ$15bn ($11bn; £7bn).