THE STUDY OF EARTHQUAKES

Press, Volume LXXI, Issue 21416, 7 March 1935, Page 12

THE STUDY OF EARTHQUAKES

<e> Guarding 'Against Catastrophe RECENT ADVANCES IN SEISMOLOGY A plea for the wider study and understanding of earthquakes by the public, and especially by public administrators. was contained in an address delivered to the Philosophical Instil ute of Canterbury by its president, Mr H. F. Baird. last evening. Mr Baird dealt with the progress already made in the study of earthquakes, and especially the discoveries made since the war.

The earliest records, said Mr Baird. showed that earthquakes were recognised, and caused fear, and this led to a certain amount of precaution being taken in' the construction of buildings. Plowever, there was little quantitative study of the subject until geology became an established science, and even now. geology was a comparatively recent science. During the nineteenth century and the beginning of the twentieth, an Englishman, Milne, with wide experience in Japan, Wiechert, of Gottingen, and Prince Galitzin did much to raise the study of earthquakes from the regions of ignorance and superstition to the realms of quantitative science. These pioneers fortunately were scattered in so many lands that they gave the widest basis to the study of seismology.

The scope of the problems presented was wide indeed, and some of them were very recondite, but many were of the closest practical interest. The seismologist knew that it was to the public interest t'.at some at least of these problems should be understood by laymen, because so many of them touched directly on humanitarian issues. All men lost when the organisation of even a remote state was upset by an earthquake disaster. Civic authorities. dwellers on low shores, inves-

tors, insurance companies, householders should all know something of the cause of earthquakes, and listen to what rcience had to say about avoiding their worst consequences. An Elastic Earth Until mathematics and . physics gave notions of the fundamental characteristics of elas'.ic impulses or waves through and round a body, no potent weapon existed with which to attack the problems of seismology. The waves emanating from an earthquake were of two important sorts. The first were the longitudinal waves set up through the compression of the earth at the point of the shock, and the ,others were waves which travelled round the surface of the earth. Astronomy suggested that the earth was elastic, and so it proved to be. Mr Baird then proceeded to demonstrate by slides, and w r ith further description, the many different types of waves set up, and their different behaviour at varying distances from the point of disturbance. Many theories had been produced about the nature and travel of these waves, and these in turn gave rise to abstruse speculations about the nature of the core of the earth, and each fresh piece of evidence required a reconciliation of views on geophysical properties. A great deal of the progress of seismology had been due to the labours of mathematicians. One school of thought was grappling with the problem of whether the moon was cast off from the earth leaving the Pacific basin as a scar, or whether it was formed from the solidification of condensible gases in the manner of some other heavenly bodies.

Another line of study of great interest to seismologists was the effect of the moon on the incidence of earthquakes. Many brilliant minds had been bent to this study, but nothing pre-eminently important had as yet been revealed. One recent investigator had shown that earthquakes were 15 per cent, more common while the moon was near the earth, but geologists and geodetists working with 'nose interested in geophysics reminded scientists that the disrupted state of the earth's blocks appeared to furnish sufficient evidence that they were a primary cause. A Mosaic A seismologist became accustomed to look at a map as though it were a mosaic pattern determined by the type and stability of the earth blocks. Premonitory symptoms of earthquakes might reasonably be expected to show in surface manifestations due to tilting and lateral displacement of blocks relative to one another, and that was why instruments were being used to record those surface tiltings, and why a network of precise land surveys was so desirable. Rough levels were useless, but precise levels were now relatively cheap and extraordinarily accurate. Anyone who could have watched the Hawke's Bay earthquake would have seen that it was merely the tilting of a block readjusting itself. The mass of the block was stupendous, and with precise surveys before and after the earthquake, it would have been possible to say just how stupendous. A wide application of the principles of geophysical prospecting might make earthquake forecasting fairly accurate in passing years, as already certain branches of this new science had shown the cause of earthquakes in Hungary. Progress in seismological interpretation had been accelerated by rrpid development in the construction of seismographs which had now reached a high degree of accuracy and sensitiveness.

The study of seismology had led to many very interesting discoveries about the probable structure of the earth's crust, and of the underlying layers right down to the core. One conclusion was that the underlying structure of the Pacific ocean area was different to that of the rest of the world, and gave added point to speculations on the origin of the moon. The exchange of accurately timed records throughout the world had led to the conclusion that most earthquakes had their origins less

than 50 kilometres below the surface, but in a few cases very deep origins had been found, one recent one having been calculated at 570 kilometres below the surface. Community Planning Wide studies were now being made into the problems of earthquakes, and it should be realised that the solid earth was not indeed solid, but an elastic earth. Internal forces, gravitation, and molecular energy were all tending to alter its shape, and to lay down the mountain ranges of the distant future. In New Zealand watch must be continually kept for symptoms of strain, and this geologists and land surveyors could now do. Much thought was being given to the problem, but against all the careful work there were the three powerful forces of carelessness, competition, and selfinterest. Community planning to break the power of earthquakes was yet in its infancy, and it was the duty of every citizen knowing the dangers and how they could be overcome to awaken interest in a problem so vitally connected with the life and well-being of the community. Only when public opinion was awakened could the services of structural engineering and other sciences be called on to play the part:: they should play in earthquake protection. Professor R. Speight and Mr G. G. Calvert thanked Mr Baird for his lecture.