SEISMOLOGY NOT NEW SCIENCE

Rotorua Morning Post, Issue 5299, 11 January 1947, Page 2

SEISMOLOGY NOT NEW SCIENCE

1 —-4 »■ PLOTTING EARTHQUAKE CALCULATION CONCERNING SUBSTANCE OF EARTH, The science of seismology, or the detection. of earthquakes, is not by any mean;st new. A Ghinese named Choke invented a seismoscope of fantastic design in the year 136 A.D. It consisted of oight dragons' hea>ds arranged in a eircle, eac'h holding a b'all in its wide open mouth. Below, were eight frogs with their mouths' open ready to receive a ball if it fell. It was thought that this wauild show if and dn wbich direcion the grolind tilted, wriee Mr. J. J. Shaw, the Birmingham seismologist. The science progressed very Jittle until some 60' or 70 years ago, when a band of British scientists in conjunction with the Japanese made many investigations and1 invented variouis types of seismograph. In 1883 Professor John Milne made his famous prediction that "it is not 'unlikely that every large earthquake might with proper apparatus be reeorded at any point on the land surface of the globe." Only ten years elapsed before this was proved to be tnue. Strangely enough, proof was not supplied by seismologist s, but by two scientists investigating the possibility that the passage of the moon caused a tide in the land as well as in the sea.

Record At Immense Distances Professor Rebur-Paschwijtz, 4n Stras'burg, and Professor Kortazzi, at Nicolaiev, in Russia, were eollaborating with very delicate apparatus. On June 3, 1893, their reconds were much distributed for several hours, the interference being later attributed to an earthquake in. Japan. Thus the h'istortc discovery was made that an earthquake could be recorded at an immense distance from the seat of the disturbance. From this date, the study of earthquake phenomena went forward wit'r rapid stri'd'es. Seismological obsef va tories were esablished in all parts of the world. It was soon recognised that all records had similar characteristics, chiefly three. A first phase of very small waves is followed soon by a second phase of lar'ger amplitude, and still later by the greates' wdves. These phases are known as the primary, secondai'y and the maxim.Lm. The d'ata concerning times of arrival of - these phases, were collected from the world-wide range of stations both hy Strasburg and Shide in the Isle of Wight. The time c'urves foi the diffei-ent waves were thus ablt to be compiled and tables --published. The primary waves travel at an average velocity of about 7 i 'lniles per second, and the secondai'y at about 3£ miles per second. The time between their arrivals gives a measure of the distance of the shock; foi instance, 3 minutes 25 seconds indicates that the shock is 1,250 miles away. An intervals of 5 minutes 47 seconeis is recorded for 2,490 miles. The velocities are not constant but increase in speed according' to the depth they penetrate and the elesticity of the n.aterial traversed. MaximiUim Wave on Surface From recorded time it was seen that these waves travelled along £ chord through the earth and not round it. The third' type of wave maintainee a steady rate of about 2| miles £ second, this proving that it travellec along the surface. The speeds of the first two types show sudden. changes from normal as the distance iricreases. From these anomalies it has been calculated tha^ the earth consists of three outer layens. The upper, the intermediate ane the lower layers are 7 miles, 14 mile; and 16 miles thick respectively. Immediately below is a solid layer o about 1,800 miles thick, and a liqui core probably of a nickelly-iron al loy, 4,350 miles in diameter. These vaiuiable anomalies, not onb in the principal time-curves, but als in those of many other types of wave reflected, refracted and transmitted have all contributed their quota to th( only hypothesis we have of th earth's interior beyond the few kil ometres of expoised surface rocks. I is thus to the credit of seismolog; that it has been able to assist geo physics more than any other science