UNDERGROUND RUMBLING

New Zealand Herald, Volume LXVIII, Issue 20867, 8 May 1931, Page 8

UNDERGROUND RUMBLING

WESTPOET DETONATIONS. ——— _ : • SCIENTIFIC EXPLANATION. •! NO CAUSE FOR ALARM. According to Mr. F. Baird, o f' the Magnetic Observatory, Christchurch, the detonations recently experienced at Westport should cause no alarm. In nianj parts of the world underground explosions of this sort have gone on for hundreds of years. Mr. Baird explained that the noises were caused by movement of the earth's outer crunfc -in relation to th<T semi-plastic material that is reached if a deep enough tunnel is dug through the solid outer crust. The movement, he said, was like the movement of the water in a lock! on a canal. The plastic material rose and fell in a similar man- ■■ ner. If the lock were to be covered with ice, the analogy would be closer. In the event of the water-level in'an ice-covered lock being lowered, a great strain would be put upon the ice. It would crack, and detonations would occur. This form of noise was quite distinct from the explosive noises caused by volcanic action. As a further analogy, Mr. Baird said that the earth could be likened to a tennis ball filled with water. If this ball had a small crack or hole in it, the water would squirt out if the ball were squeezed. If the ball, had no crack, and enough pressure were applied, it would bulge out of shape in certain places. The cracked ball was analogous to a volcano, and the othijr action to an earthquake. "I very much doubt if the full moon has a great deal to do with causing the noises," said Mr. Baiinl. "It is quite probable that tidal action has something to do with the noises, but Ifc would be by no mean 3 the only cause. There are other very potent causes which have been neglected." Mr. Baird recently returned from an inspection of the district affected by the Murchison earthquake, and says that rumblings are still going on in the Murchison and Golden Bay districts. On the eastern coast of the United States the Indians had noticed rumblings in certain places for hundreds of years, and in other parts of the world the same phenomenon had been noted over long periods. ® "This does not mean anything extraordinary," said Mr. B.aird. "It certainly does not mean that there is a> big shake corning, or thzit there is volcanic activity." / The whole subject of earthquakes wa?i so vast that relatively very little wan known about them, Mr. Baird continued. Scientists all over the world were at work on earthquakes, but the subject was so big that it had not been gone into fully yet. It was known, .however, that earthquakes were caused by the rising or falling of the semi-plastic layer which extended right round the earth at a depth of 40 kilometres. This movement imposed strains on the solid crust of the earth, and fractures or bulges resulted, sometimes causing earthquakes.