CAN EARTHQUAKES BE PREDICTED?

Dominion, Volume 35, Issue 270, 13 August 1942, Page 4

CAN EARTHQUAKES BE PREDICTED?

Is New Zealand Likely To Sink Into The Pacific?

SCIENTIFIC VIEWPOINTS (By L. Bastings, D.Sc., Fellow of the Institute of Physicists, London; former Demonstrator in Electricity, Cavendish Laboratory, Cambridge, etc.).

One of the chief topics of conversation in the Dominion today is earthquakes, and the questions most frequently asked are: (1) Can earthquakes be predicted? and (2) Is New Zealand likely to sink into the ocean one of these days? Dr. Bastings answers these questions in the following article, which has been released for publication by the New Zealand Association of Scientific Workers. The prediction of earthquakes has always had a fascination for the. popular imagination, and many attempt are published from time to time at earthquake predictions. But a examination of such claims invariably reveals that they rest on inadequate foundations. It seems unlikely that earthquake prediction will ever be really possible. In order that a prediction should have any claim to consideration, it must state both the time and the place of the pending occurrence within reasonably narrow limits, and also must give some estimate of the severity of the shock. Earthquakes which can be felt are occurring every hour in some part of the earth, and instrumental evidence shows that shocks of minor intensity are still more frequent. Of these three factors in a prediction, one, the place of a future major shock, may perhaps some day become known, when our knowledge of the immediate and ultimate' causes of the phenomenon are much more thoroughly understood. But we must first be able to (follow instrumentally the gradual building up of the strain which, as we have seen, is believed to be the immediate cause of many earthquakes. But we are never likely to be able to predict just how fast this process is likely to proceed, or how far it may go before teaching the limit, nor yet what incidental factor may in the end upset the balance. No Earthquake Weather.

Attempts have been made to correlate major earthquakes with phases of the moon, with the tides, with spots on the sun, with, changes in barometric pressure, and with other such natural occurrences. None of these has been proved to the satisfaction of the scientist to have any clear influence on the course of events. The very popular belief in “earthquake weather” has no justification in fact; earthquakes of all intensities have been recorded under weather conditions of the most diverse kind.

It cannot be denied that unusual features are frequently observed at about the same time as some earthquakes. And it is very tempting to ascribe to such events the role of cause, or effect, of the earthquake. Close examination has very frequently shown that such correlation is without adequate foundation. Unusual natural phenomena are of frequent occurrence, though they often pass unnoticed except by the few. There may be some correlation between earthquakes and peculiar behaviour of animals, or unusual meteorological conditions, or extraordinary illumination in the sky, but no satisfactory connexion has yet been established; nor has any repeated occurrence of this kind been correlated with severe earthquakes in any part of the world. Reports are frequently forthcoming from observers who claim to have seen waves on the surface of the ground during an earthquake. When it is realized that the distance from crest to crest of the shortest of these earthquake waves is more than a mile, while the actual displacement is at most only a few inches, it will be seen that such reports must be due to some kind of illusion. The suggestion has recently been made that the passage of these rapid vibrations over the surface of the ground might cause corresponding pressure waves in the adjoining air, which in turn might alter the refraction of the air in such a way as to give one the impression of visible movement of the ground. Such reported movements have never been recorded instrumentally, although suitable instruments have been set to record them on many occasions.

Will New Zealand Disappear?

Several of the major New Zealand earthquakes have produced noticeable uplifts of tbo ground over an extended area. The 1929 Buller earthquake resulted in a maximum uplift of about 16 feet; and the 1848 earthquake is credited with uplifting the Te Aro flat to sueh an extent as to make the Basin Reserve unsuitable as a prospective basin for deep-sea shipping. Many people are prone to infer from this that some day the reverse process might occur and that New Zealand might gradually, if not rapidly, disappear into the oeean. There is no foundation whatever for such a conclusion. Circumstances which might produce a subsidence are entirely different from those operating now in this part of the world. And in any case, the amount of energy involved in such an imagined catastrophe is vastly greater than that released even in the most violent earthquake. For it is now quite clear that there is an upper limit to the amount, of energy which can be released in anyone earthquake, corresponding to the maximum strain which the upper layers of the earth are able to sustain. On the other hand, the energy that would be released by a general subsidence of the whole country may readily be shown to be many tens of thousands of times as great, as this. At the rate of one major earthquake every 10 years or .so, it would take at least a million years for sufficient energy to be released by earthquakes to amount to as much as —Quid be involved in a general subsidence. We naturally regard disasters such as the recent earthquakes as colossal disturbances; but. in the mysterious and slow-moving changes of nature, they are merely incidents of very small moment.