'QUAKES IN 1932

Rotorua Morning Post, Volume 2, Issue 434, 19 January 1933, Page 7

'QUAKES IN 1932

OVER ONE A DAY NO CAUSE FOR: ALARM IN DOMINION OBSERYATORY RECORDS. EVER PRESENT TREMORS. The half-dozen or so seismological instruments at the Dominion Observatory, Wellington, recorded 461 earthquakes during the year. Alarm need not be felt at this statement, for the average number recorded has always been well ovef one a day, and 1932 was not at all remarkable for its 'quakes. The very great majority of those recorded were not felt hy anyone, and needed a delicate instrument to record their occurrence. Of the 461 shocks, 281 had their origin in or near the Dominion, the other 180 being the traces of shocks which oecurred in other parts of the world. The most serious shock in the Dominion during the year was that at Wairoa on Septemher 16. Of the long-distance shakes recorded, by far the biggest was that which happened a few days ago, and the origin of which is still to be ascertaiaed, no place as yet having report'ed a devastating shake. - All the records made of the 1932 j 'quakes are preserved for future study | and comparison with; records obtained ! elsewhere. It is by this- study that j a science of earthquakes is slowly be- | ing built up, as well as a knowledge j of the deep-seated structure of the j earth. Seismologists can read quite a lot from the little tracings that the various kinds of earthqualce waves make on the photographic paper of the recording instruments, and al- j though man will never be able to pre- I vent earthquakes, it may he possible some day, when the science of seisj mology has progressed a little fur- | ther, to predict them with a fair de- ' gree of accuracy and to locate, and so , | avoid building on, danger zones. | The deductions which can be made j by seismology as to the structure of ! the earth are being put to good use by geologists in a commercial way in their endevours to locate oil strata. To look upon seismology as a useless branch of science is to display lamentable ignorance. i ! Seismometers at Work. J | Science has moved a long way since 132 A.D., when a Chinese savant of the name of Chang Heng invented the first earthquake recording instrument. He erected a suspended column which was free to move in eight different directions. Balanced on it were eight balls with cups beneath them. When the quake came along the column moved in the direction of the shock, and any ball reposing in a cup indicated to Chang Heng the direction from which the shock had come. Modern earthquake recording machines date from 1841, and have of recent years been much impyoved. The earth is never at rest; there are always shocks occurring somewhere of greater or lesser intensity. Seldom does a day pa'ss without the Kelburn seismometers registering a 'quake somewhere or other. The more sensitive instruments record perpetual "microseisms," minute vibrations caused by waves beating on the coast. Some of the instruments are designed to record horizontal shakes, others vertical ones, and "tiltometers" record the tilt of the land caused by an earthquake. What is of most interest is the manner in which seismologists deduee facts about an earthquake from the series of wavy lines which the seismometers record. Upon the occurrence of an earthquake there go out in all directions waves or vibrataions. In a very big 'quake these vibrations have been known to travel twice round | the earth and to be still detectable. They may be compared to the ripples going out on all sides from the point where a stone enters the water when thrown. As these waves broadcast by an earthquake happen to be of three very distinct kinds and travel at three distinct rates, the reading of their story is made somewhat easier than it might otherwise be.