THE RECENT EARTHQUAKE

Dominion, Volume 16, Issue 163, 28 March 1923, Page 7

THE RECENT EARTHQUAKE

DR. C. E. ADAMS’S DEDUCTIONS All .the available information about! the earthquake of March 18 and its predecessor on Friday, March 16, has bpen gathered by Dr. C. E. Adams, Government Seismologist,' and worked into a chart to show where, the disturbances originated, and it is clearly shown that the Friday shake came from very close to Wanganui, and the Sunday one from directly beneath Wellington, or ,its immediate environs. The method of making such a chart, is to mark on a map the places where the earthquake is observed, noting the intensity of tile shock, as determined by the observer, using a well-known arbitrary scale, which is in general uso for the purpose. Places where] the record gives the same intensity are then joined by a line,, and the result is a series of curves which in an ideal case’ form rougTi circles, and show the greatest intensity at the innermost ring and a regular diminution outwards. The map shows two sets of curves, one enclosing Wanganui, and the. other Wellington. These locations are confirmed, so far as they can be. by' the records made by the seismograph at Kelburn. The Friday record shows a short series of preliminary tremors before the main shook arrived. From the length of the preliminary train the distance of the origin can be calculated with fair accuracy for a distant origin, but with less accuracy for one close at hand. The preliminary train is in this instance too short for accurate calculation, and Dr. Adams estimated at the time that the origin was about 100 miles away. It was a good estimate. Wanganui is approximately 100 miles from Wellington. The record of the Sunday shock is a most striking one. It proves conclusively that, however many shocks and bumps people think they felt; the instrument felt only one jolt, with neither preliminaries nor subsequent vibrations. It is, in fact, a record of a very rare type. The wavy line recording the shake is precisely similar in form to that made by the artificial “shakes” which are e mado daily for testing purposes, and which consist of a single slight tilting of the instrument. The only difference between the natural and the artificial record is that after the shake the seismograph showed that the ground had been, slightly titled towards the west—an affliction from which it has since been slowly recovering.