WHY EARTHQUAKES HAPPEN,

Hokitika Guardian, 1 November 1923, Page 3

WHY EARTHQUAKES HAPPEN,

A great oartiiqunko i i one of the most terrible experiences to which human beings can be subjected. After the catastrophic disturbance u) October -lith, Iktii. in Japan. ligt.dreds of people who showed no sign of external injury died ol shock. In a minor earthquake the horizontal movement of the ground is usually less than it tenth of an inch. In too Dftl e;irtiKt!ial;f' m Japan, which the cartliquako last week at Toltiu possibly exceeded, the ground moved nine to ten inches horizontally. Ihe movement was visible t'i the eye and was accompanied iiv terrilic noise.-.. Earthquakes ot great, magnitude, such as this, are the manifestation of some elemental disturbance, probably deep within the eaith's -pheie. We know two (vrtain farts regarding the interior of the earth. It is very hot. ami it is enclo-. ■! by a thick metaiiie shell, wliicli is prohafily composed of nickel steel. The inmost, interior is probably gaseous. On the surface ol 1 his metallic shell is a t Inn t rust ot rock, which is radioactive, and not more than forty miles deep. Thiei list may he compared with the pieces of a jig-saw puzzle: it rises and sinks according to tie- movement of the metallic shell. This inner metallm shell is constantly losing heat, and is consequently steadily cooling ami shrinking so that the outer cru.-t lias to shrink with it. Tim

ell'ect of shrinkage on the outer cruse is that this is forced up and down. Astronomers, and mathematicians .••lid geologists at'..’ it"', for Ihe most part agreed that in the really terrible enrhomiki's some iiirtlo’r cause other tinii • Irinka-".' is at work. Thi- seems In im the so cidiml “wobbling” of tlm earth’s poles, which alter their position slightly, and ibn- vcvv the ‘dress tlm iumicii-e rapidly-spinning hall ol steel, with catastrophic re-dills where there is anv weakness developing in that hall. As to the i. l"it rii : 1 phenomena which uicouipanv great ,:: rl ii'jiia!.- s, everyone who has been ihriiigb a shock knows teat they a v real..and ii im- very recently I Men discovered tint it qimriz is pressed hetw'een two sheets of metal a free elc-irm charge, correspuiiding ti the pressur". nuimi'esi..; itsell in the sheets. Where tlm pi.--.nv is on a stupendous -rale as in a great earthquake, thi-. is s 11 11 i<■ i" 111 to produce violent ha rieal ireivcmeuts. I lea mlerstoi iiis and typhoons. Tidal waves, another ear! !c;!Ui!:e. aceompaniuient. are the resiilt of the tremendous vibrations of the earth and Ihe for ret :011s of let el ii Ihe sea. In gnat earthquake, the vibrationcontinue .••’••ere l-m a collide of hours, v, lieu they slow i\ '!:.■■ low n. Iheea i t li. hov.'el el' i 1: me OI.'I I erniiii li' lls i - always vihratiog -lightly. It may he compared with a huge eir-. lllar boil u under ii i: Ii I’ -11" . cud del aa I • -el--moulders I v rv large—rob- barometers give seme idea cf tlm |ii;!-attons ip 1! ■ interior. ! ! biilt Mall >