Parts of the country have been hit by a tsunami, however there is no need to run for the hills.

The National Institute of Water and Atmospheric Research says the half metre wave was generated by a huge earthquake in the northern Pacific Ocean just over a week ago. Fourteen hours after the magnitude 8.3 quake, the initial wave reached the Chatham Islands and the Bay of Plenty, 9600 km from the site of the quake.

Its journey across the Pacific was measured at an average speed of 685 km/hr. By comparison, a Boeing 737-300 travels at 790 km/hr.

A couple of days later it was recorded at Timaru, Lyttelton and Kaikoura. The tsunami affected New Zealand for over a three or four day period as waves bounced off undersea ridges such as the Chatham Rise, and moved to and fro along indented sections of the coast.

Dr Bell says if it had happened during a storm with very high tides it might have been a bit more of a nuisance, but as it was its effect was minimal.

Around the Pacific, the tsunami impact was greatest at Crescent City in northern California, where a peak wave height of 1.76 metres caused strong surging currents, damaging docks and boats in a marina.

The graph above shows the tsunami measured at four New Zealand sea level gauges. The tide has been removed to isolate the tsunami waves. Data from Timaru are supplied by the Port of Timaru, while the other sites are NIWA gauges. ‘EQ’ marks the time of the earthquake in the Kuril Islands.