EARTHQUAKE DETECTOR

New Zealand Herald, Volume LX, Issue 18317, 6 February 1923, Page 9

EARTHQUAKE DETECTOR

THE .MODERN SEISMOGRAPH.

INSTALLED AT WELLINGTON

PHOTOGRAPHIC PRINCIPLE.

~V'' ■'. What we arc all aiming at is being able . to ... predict earthquakes,',' stated Dr. Adams, Government - astronomer, when ■■'. interviewed at Kelburn ; Observatory,. Wellington, alongside which preparations are now being made for the installation of a new seismograph,! or "earthquake detector," as it might be called. " Before we can hope to'- do that, however, we have 'to follow the ordinary scientific course, by proceeding to collect precise data of what is happening in the earth.i: Wo therefore need : a delicate instrument which will at once record and measure all the thrusts, strains, tremors, and quakes that take place; and by studying thousands upon thousands of these records, measuring and comparing them with : infinite care, we may hope to be able, at length to say that such and such a record means that an earthquake is due within a longer or shorter period of time. . . •• > ■ " That is why we are now preparing to install alongside the observatory, a MilneShaw seismograph— is to say, a Milne seismograph as improved by Mr. J. J. Shaw. This is the machine recommended by the chief British seismological authority. We had the machine installed temporarily at the Victoria College for exhibition at the Science Congress; but a permanent home is to be built for it here aT the observatory. That big pit you saw being dug beside the 1 door of the observatory is for a concrete block or pillar, 12ft. hign, on which the seismograph will.rest, so as to be free from mere surface vibrations "

Most Sensitive Instrument. A number of the daily records made by the machine at Victoria College were exhibited by Dr. Adams, who stated that it is 40 times as sensitive as the old Milne machine, which was previously the only seismograph in New Zealandi ■ "The xesult is,'* he said, " that working with the new machine is like working with a microscope 40 times more powerful than you have been used to working with. You will note (comparing the records) that the records of the old machine show only a straight line till a distinct quake is registered; but the new machine shows a serrated line, like the teeth of a small saw, demonstrating that the crust of the earth is in constant motion. That is to say, there aro incessant minute oscillations of the ground. You will note, too, at larger or shorter intervals, a movement of the whole line to one side or the other by about its own width.. That seems to indicate a sideways thrust, easing off when the line comes into position again." ."And what is that big jump of about a quarter of an inch, first to one side and then to the other?" was a question asked. " That," replied Dr. Adams, "registers where I stood first at one side of the machine, and then at the other. That shows how extremely sensitive the machine is, though its foundation is supposed to be quite isolated from the floor of the room. On January 22, Anniversary Day, you will note a distinct earthquake was recorded. From the oscillations ; shown I should judge that it was some considerable distance'»away, possibly .in the direction '■" of Tonga, where we get a lot *\ of earthquakes. The one machine, however, can only indicate the radius within which the earthquake occurred, not its direction, north, east, south, west, as the case may be. The direction will not be obtainable until a second machine, mounted at right angles to the first, is available.

Photographic Records. "In the case of the new machine the tremors are recorded photographically by a beam of light, reflected on a particularly sensitive mirror and: then thrown back on.',.■' to v a recording drum, covered with bromide paper and revolving in a light-tight box, or camera. There is thus no friction in the recording of the movements, each- as is inevitable when the record .i is .'" made by means, of a : pen on a revolving drum. When we have accumulated a large number of these records i we shall be able to study and ; compare them, so as to understand what they mean m the way of, changing y thrusts and strains and various movements of the earth's crust; and we hope that gradually this study..... of . the records £ will lead up to our being able to predict both when and where earthquake* are coming. " The record - islips of bromide -paper are changed once a day, each slip wound round the drum giving us. a record for the whole 24 hours. ; Then - the records have to be developed like any other photograph. It is very interesting, in fact, in its way, exciting work. You know what it is to -go fishing, with what 'excitement you watch your line or rod for an indication of a nibble or a bite. Well, ; I watch, the development of the records, for a tremor or an earthquake with just as much excitement as a fisherman.watches his line or his rod. It is, in a way, fishing for earthquakes." . ; v .