A Waikato University scientist says if New Zealand is serious about reducing risk to people and places following Christchurch’s earthquakes, then Northland is the most sensible place to be building a new city.

Associate Professor Earl Bardsley from the Department of Earth and Ocean Sciences says while large earthquakes are rare, Northland has considerably fewer earthquakes because it bends away from the main seismic zone.

“The Christchurch earthquake has forced us to think how cities should be built and where they should be located. The rest of the country has a higher overall risk of urban destruction.”

Dr Bardsley says rather than focus on the complex seismic detail of individual earthquakes at different localities, it is simpler to consider this risk as an average in terms just of those few important earthquakes which have resulted, or will result, in extensive urban damage.

Image of the advertisement from the Christchurch Press, promoting Northland as a desirable place to relocate your family and business.

“The data set of past major urban destruction events in New Zealand is very small, but we can make use of the 1931 Hawke’s Bay earthquake and the 2011 Christchurch earthquake. Taking their 80 year separation as a rough indication of the mean time between random urban-destructive earthquakes, the chance of at least one such event outside of Northland in the next 60 years is greater than 50 percent.”

Northland could become a seismic retreat for some of New Zealand’s future urban development, says Dr Bardsley. “The risk for the rest of New Zealand will change somewhat if the mean between-event time is taken to be other than 80 years, but is still likely to be sufficiently high to impact on New Zealand’s earthquake insurance premium. In fact, New Zealand cities from Auckland south can be thought of as having to pay a long-term ‘earthquake surcharge’, being the ongoing amount required to fully repair damage to buildings and infrastructure after each event.”

For Northland, the situation appears much better, with perhaps as long as 500 years between destructive events. “This creates lower earthquake surcharges and raises interesting questions about the best national response to Christchurch’s quake,” says Dr Bardsley.

He says a new city based around the Hokianga might result in Christchurch decreasing in population but that need not mean it would be any less pleasant. “There would also be the advantage that a new Northland city would draw off some of Auckland’s growth and reduce demand for its infrastructure development. It may even happen that a new city in Northland eventually becomes the nation’s new capital, on the basis that any capital city should be in the least vulnerable location and near the centre of population.”

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