THE WELLINGTON SEISMOGRAPH.
HOW IT RECORDED THE EARTHQUAKE.
(SPKCI.VL TO "THE PRESS.") WELLINGTON, April 20. Shortly after 1 o'clock yesterday tho Government seismometer at Mr G. Hogben's residence, recorded the flirt tremors of the earthquake. The timo— 1.2 a.m.—corresponds with 5.32 a.m. on the 18th at San Francisco, and if the earthquake occurred at 5.16 a.m., as stated in the cablegrams, this would allow sixteen minutes for the waves to travel from San Francisco to Wellington. The recorel of the shake shows it to have been a very violent one. and almost, as Ixid as that which occurred in Guatemala, in 1902. The instrument r ■'•curded the passage of the waves round the earth five times, at iutervals of about three nnd a quarter hours. The damage was clone by the very slow waves which l>elonged to the fifth of the eight phases in which an earthquake is separate!, and these would start from the point of origin, very soon after the fine wave*, at a speed of between two and two and a half miles a _ex*ond. The strain of tho rocks was greater just before breaking, and the vibrations that wer© then produced wer© the most rapid but small. Jiust after fracture, a movement of the rocks took place. They slipoed, and the resultant vibrations were much bigger and much slower than the preceding one, because tho stress was not so great.
There was another interesting series of transverse waves, due to the change in the form and position of the rocks after th© initial shock. Th_o were the slowest waves of the series. The first of them took 90 minutes to cross the Pacific. 80 minutes longer than tho first fine wave.*-. The great distance of New Zealand from the seat of the disturbance makes it very difficulty to c!~----termine the duration ot the eartiiquake, as the wave-* overlap confusingly on the
tape. An earthquake in or near New | Zealand, however, could be accurately gauged, because the caries ot waves would be too distinct to bo confused.
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Press, Volume LXII, Issue 12484, 21 April 1906, Page 10
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340THE WELLINGTON SEISMOGRAPH. Press, Volume LXII, Issue 12484, 21 April 1906, Page 10
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