EARTHQUAKES.

Hauraki Plains Gazette, Volume XXXIV, Issue 4615, 17 October 1923, Page 2

EARTHQUAKES.

WHY THEY HAPPEN. (By the Scientific Correspondent of the Daily Mail.) Earthquakes pf great magnitude are the manifestation of some elemental disturbance, probably deep within the earth’s sphere. We know two certain facts regarding the in--terior of the earth. It is very hot, and it is enclosed by a thick metallic shell, which is probably composed of nickel steel. The inmost interior is probably gaseous. On the surface of this metallic shell is a thin crust of rock, which is radioactive, and not more than forty miles deep. This crust may be compared with the pieces of a jig-saw puzzle ; it rises or sinks according to the movement of the metallic shell. This inner metallic shell is constantly losing heat, and is consequently steadily cooling and shrinking, so that the outer crust has to shrink with it. The effect of shrinkage on the outer crust is that this is forced up and down. Astronomers, mathematicians, and geologists are now for the most part agreed that in the really terrible earthquakes some farther cause other than shrinkage , is. at work, This seems to be the so-called “wobbling of the earth’s poles, which alter their position slightly, and thus vary the stress on the immense, rapidly-spin-ning ball of steel, with catastrophic results where there is any weakness developing in that ball. As to the electrical phenomena which accompany great earthquakes, everyone who has been through a shock knows that they are real, and it has very recently been discovered that if quartz is pressed between two sheets of metal a free electric charge, corresponding to the pressure, manifests itself in the sheets. Where the pressure is on a stupendous scale, as in a great earthquake, this is sufficient to produce violent barometrical movements, thunderstorms, and typhoons. Tidal waves, another earthquake accompaniment, are the result’of the tremendous vibrations of the earth and the alterations of level in the sea. The earth, however, in quite normal conditions is always vibrating slightly. It may be compared with a huge circular boiler under high pressure, and delicate seismometers and very large-scale barometers give some idea of the pulsations in its interior.