Survey shows one-fifth fled city

Cellphone records show about a fifth of all Christchurch residents fled the city after the February 22 earthquake.

A study by Statistics New Zealand, based on records from two of the country's three cellphone networks, has found that 20% of the cellphones that were used in Christchurch city in the 10 days before the earthquake were used outside the city in the week after the quake.

Many people fled only to the surrounding areas of Canterbury, but between 8% and 10% of those who left made cellphone calls in Otago and about the same proportion in Auckland, with Wellington a close third.

Only 2% of the callers went to Marlborough and about the same number to the West Coast.

The study is unusual internationally because cellphone companies in most countries have kept their calling data secret.

Kirsten Nissen, a Christchurch-based Statistics New Zealand analyst who co-ordinated the study, said the two local networks understood the public value of their data. The third network, which she did not name, refused to co-operate.

The two networks provided records of all cellphone calls in February, March and April last year and this year, allowing a comparison of post-earthquake calls with the pattern in a normal year. In most weeks last year, about 5% of Christchurch-based cellphones were used outside the city.

This year the number jumped to 20% straight after February 22, but then fell back to about 7% by April, showing that most people who left returned to the city within two months.

However, the numbers were still notably higher than at the corresponding time last year in Auckland and Otago, showing that some have still not returned.

Statistics New Zealand estimated last month Christchurch's usually resident population fell by 8900 people, or 2.4%, in the year to June.

Project manager Adele Quinn said the estimate was based on data of births and deaths, international migration, enrolment in schools and primary healthcare organisations, electoral rolls, electricity consumption, Earthquake Commission data and tax-based employment data, as well as the cellphone study.

 

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