Auckland Is Not Free From Risk Of Earthquakes

Auckland Star, Volume LXXIII, Issue 165, 15 July 1942, Page 4

Auckland Is Not Free From Risk Of Earthquakes

THE recent Walrarapa earthquake * came as a further reminder to us of the relative instability of the earth's crust. New Zealand has had her share of these catastrophies in common with other lands, but it must not be supposed that New Zealand is any more susceptible to such destructive agents than scores of other countries.

By A. W. B. Powell

In the Pacific, major earthquakes are likely to occur anywhere along a vast circle of structural weakness that margins the entire Pacific Ocean. The Napier, Murchison, Wellington (1855), Tokyo, San Francisco and many South American major earth movements all occurred along or adjacent to this vast line of weakness. One great consolation is that seldom within living memory has any one locality along this line of weakness suffered a second disaster of first magnitude—which means that once pent-up stresses are relieved there is a likelihood of a subsequent long period of quiescence. On the Profit Hide Occasionally, by taking the broad view, earthquakes may be considered to render a service to mankind, in that there is a profit as well as a loss account. In the Wellington (1855) 'quake, for Instance, the snore line of Port Nicholson was raised sft, thus providing a level shore platform in an otherwise precipitous area, and this platform has now preat.ly facilitated the roading prob-

The Napier disaster was much more destructive owing to the population density Involved as compared with the sparse Wellington settlement of 1855. Even in the case of Napier, however, there has been some compensation in respect to the uplift of the former shallow inner harbour, making possible its subsequent transformation into a rich agricultural and part residential area.

The cliffs bounding the inner harbour are of mid-pliocene marine sediments which by the evidence of contained fossil shellfish were laid down offshore In from 10 to 30 fathoms, approximately 12,000,000 years ago.

Human record compared with geological time Is Infinitesimal, out there remains the evidence that over a long period of time this part of New Zealand has been rising— not continuously, but spasmodically, just as the complex forces involved will allow. Auckland's Position Auckland, throughout its hundred years' history, has escaped an earthquake experience of any magnitude, but there is evidence that this immunity cannot be a permanency. Our coastal topography shows abundant evidence of earth movement and uplift even up to comparatively recent times.

From accounts obtained from Maoris in the early years of the Auckland settlement it would seem that an earthquake of first magnitude had been experienced on the Auckland isthmus some years prior to European settlement.

In many parts of New Zealand uplifted sea bed containing fossil shells Is a feature of the countryside. MaSterton, which has had more than its share of 'quakes, id no exception, for fossilised shells of tertiary age may be seen in innumerable road cuttings and limestone outcrops on the surrounding hills.

Forty miles east of Masterton on the coast there is a magnificent reef of shell limestone which forms the headland upon which the Castlepoint lighthouse stands. This reef tilts at a decided angle towards the land, showing how cumulative uplifting forces bring about substantial changes in local topography.

Local earth movements, however, are not always of a positive nature, for some areas have experienced series of movements of a subsidiary nature. This is true of Marlborough, where the Waiau plain subsided during the 1855 'quake to approximately the same amouht that the Wellington coast Was uplifted.