SOLID EARTH CORE

Evening Star, Issue 21723, 18 May 1934, Page 5

SOLID EARTH CORE

CONCLUSION REACHED AFTER N.Z. INVESTIGATION

SCIENTIFIC DEDUCTIONS OF INTEREST 'Remarkable deductions relating to the nature of the earth’s core, made as a result of investigations in New Zealand, were revealed at a special meeting of the Wellington Philosophical Society convened for the purpose of. affording members au opportunity of meeting Mr L. Bastings, M.Sc., F.Inst. P., and of hearing an account of some important discoveries in seismology recently made by him.

The lecturer introduced his subject by reviewing the types of earthquake waves which spread out to great distances from a major distuibancc. The first of these to arrive at a distant station was found to fade out at distances greater than about 107dcg, he said, but appeared again in a slightly altered form near the Antipodes. A detailed analysis of this wave led Gutenberg in 1914 to the conclusion that the interior of the earth contained a central nucleus or core about 4,400 miles in diameter, composed of , material very different in nature from that external to it. EXAMINATION OF RECORDS. The shear of distortional waves whicH followed later in the sequence might be expected to penetrate this core and appear on records ou the far side oft the earth as a double impulse, the expected time and other characteristics of which Gutenberg deduced from his theory. Repeated search in the last twenty-nine years for signs of these phases at great distances had proved futile ; and consequently the idea had gradually, grown up and become firmly/ established that this pointed to the material of the core being incapable ofi transmitting shear waves . owing, to its being in a liquid or semi-fluid state; hence had arisen the accepted opinion that the centre of the earth was composed maiiily of molten iron, an opinion which had gained the support of the leading geophysicists of the world. In the last, few years, however, scanty evidence to the contrary had been put' forward by the American, Macelwane, and the Japanese, Imamura. ; But tha former had expressed himself as dubious of the adequacy of his evidence; and the latter based his conclusions on a single isolated observation which is certainly insufficient to settle so fundamental a controversy. -

NEW ZEALAND INVESTIGATIONS. Mr Bastings described his own investigations into the material provided by some fifty European seisinological stations from the 1929 earthquake in the Duller district of New Zealand. Among . this material, he said, abundant evidence was forthcoming that shear waves did penetrate the core and appear on the far side. In four distinct respects these movements confirmed the predictions ' regarding them. They _ arrived suddenly in the expected neighbourhood; appeared first as very prominent movements according to theory; separated into two distinct branches; and had travel times which indicated a rigidity. in the core material agreeing most remarkably with that of the extra nuclear structure. It was very infrequently that an earthquake of great magnitude occurred in-such a locality that all the conspired to provide the requisite evidence; and. the earthquake under discussion was probably the first in seismological history to present the facts with a continuity and completeness that made identification of these movements reliable.

AN INEVITABLE CONCLUSION. From the facts presented the conclusion seemed inevitable that the earth s core transmitted shear waves like a solid, and did not damp them out after the manner of a liquid. Thus an international controversy of twenty ' years ■ standing had' reached a definite conclusion as the, result of ’ an- investigation undertaken in New Zealand arid • with material derived from .an event originating in the dominion. The meeting was presided over , by Dr Adams, Government Seismologist, and a number of members spoke ■in terms of appreciation of the excellent quality of the work reported by the lecturer and of the world-wide interest likely to'focus upon so fundamental an advance in seismology. '

■ [Mr L.- Bastings is at present in Wellington in connection-with the publication of some investigations he has just completed regarding- various aspects of the Buller earthquake of 1929. Mr: Bastings was for some time working with Lord Rutherford at Cambridge. Since returning to New Zealand he has turned his attention to seismology, and has just reached a fundamental conclusion of world-wide interest regarding the interior of the earth from evidence derived from the study of earthquake movements. In recognition of his pioneer work in this direction he has been, appointed an honorary associ. ate in seismology at the Dominion Observatory. 1 This is the first .distinction of its kind to be awarded in seismology, in New Zealand, and only the third occasion on which the honour_ has been bestowed, the previous occasions being confined to astronomy.] ,