EARTHQUAKE TREMORS

Taranaki Daily News, 30 January 1930, Page 9

EARTHQUAKE TREMORS

"’long distance waves FROM MURCHISON TO OTTAWA. MORE SEISMOGRAPHS NEEDED. Through the courtesy of the director of the~ Canadian Seismological Observatory at Ottawa, an -interesting record the New Zealand earthquake of last June, as observed in Canada, hae become available for inspection by New Zealand seismologists. The actual chart taken from the Ottawa seismograph is in the possession of Mr. W. F. Robinson, F.R.G.S., lecturer in engineering at Canterbury University College, and it traces with great distinctness the arrival of the earth tremors after travelling nearly half-way round the globe. The earthquake commenced at Murchison at 10.17 a.m., according to observations taken at the Christchurch Magnetic Observatory, and the first intimation of the earthquake was recorded at Ottawa 211 minutes later. These yraves, called brachistochrone waves, travelled more or lees through the earth, writes Mr. Robinson in an interesting commentary, and followed a path which allowed of the shortest time of travel, being reflected from the inner or concave surface of the earth s shell. Ih-o velocity of the waves must have been about 12 miles a second. ARRIVAL OF ‘’EARTH ROLLERS.” A second series of energy waves, known as transverse, after being once reflected, arrived 18min. after the flrat, while the same waves, after being twice reflected from the earths surface, arrived after the passage of a further smin. After another interval, of llmin., or 44min. from the arrival of the first waves, the long waves or earth rollers arrived. These probably travelled through the outer shell of the earth, not far from the surface, a course-which fa not that of the shortest time of travel. They had a large amplitude find continued for about half an hour, o,t the end of which they began to fade until they became practically insensible nearly four hours after the first record was made. ‘ Mr. Robinson, who acknowledges his indebtedness to Mr. H. F. skey, director of the Christchurch Magnetic Observatory, for much of the above information, fovives the question of establishing inore seismographs in New Zealand. “It is to be hoped that the Government department concerned will adhere to the £ood resolutions it made while the ground was still quivering beneath it Ind will bring the seismological observatories of the Dominion _ move up-to-dnte,” he said. “I doubt if the establishment of only one up-to-date and instrument at Wellington will suffice. Useful as it might bo for the record of a distant earthquake or for minor local shakes, the record of an important earthquake whose epicentre was near the instrument would probably be off the scale. INSTRUMENTS IN COUNTRY. ‘'Scattered stations, even if fitted with simple instruments, .can, in the hands of intelligent observers of no great Specialised scientific knowledge, give valuable information. Since time is a very important part of the record, it tvould. seem that at various country post offices there should be installed secondclass (not second rate) instruments, of the self-starter type if desired, and {hat a I‘ttle more responsibility still Should be laid on the shouldern of the postmasters, who already have enough to do. These officers, by their training And o-eneral standard, are the best fitted 6f tlTc civil servants to have, charge of those instruments. “It should be remembered that in Japan seismology has reached a stage At which it is said to be possible to predict a coming important earthquake ■With reasonable certainty some days beforehand,” Mr, Robinson adds. “There ■aro authenticated cases where the lower animals have had instinctive premonitions of earthquakes and other geo'physical disturbances, therefore it should be quite possible for man to get eame warnings instrumentally.