EARTHQUAKES

Wairarapa Times-Age, 4 August 1942, Page 6

EARTHQUAKES

SERIES IN NEW ZEALAND THOUGHT DUE TO ADJUSTMENTS. COMMENT BY SEISMOLOGIST. (By Telegraph—Press Association.) WELLINGTON, This Day. “On the fuller data now available it is possible that the original estimate of the strength of Sunday’s earthquake as 7 plus at Wellington was a little under-estimating it,” the acting Dominion Seismologist, Mr Hayes, said yesterday afternoon. “The figure of 8 on the scale may ultimately by found mere correct. Earthquakes of the latter strength are fairly common in New Zealand and they are not always followed by aftertremors. “While the earthquake of June 24, centred in the Wairarapa, for which the strength estimate has been placed at 9 plus at the epicentre, can certainly be classed as of major magnitude, there is no evidence as yet that would suggest Sunday’s disturbance was of the same order. The June 24 quake was followed by a large number of after-tremors, running into several hundreds in the first 24 hours. Up to 9 o’clock this morning the seismographs at Kelburn have only recorded about a dozen after-tremors to Sunday’s shake, and only one of these was of sufficient strength to be felt locally or noticed by such things as rattling windows or creaking walls.” Discussing the damage caused by the latest disturbance, Mr Hayes said it was possible that its widespread nature and seriousness was due to the fact that its direction differed slightly from that of June 24, and the strain placed on the already damaged buildings therefore fell in a different way. SEQUENCES REVIEWED. Reviewing the sequence of earthquakes in New Zealand. Mr Hayes said that records over- the past century showed that in the years from 1843 to 1855 there was a series of disturbances of strength 10 on the scale, with quite a number of strength 9. After that, till 1929. there was a quieter period, with occasional shocks of strength 9. In 1929 began a five-year period of heavier disturbances, which included the Buller (Murchison) , Hawke’s Bay and Pahiatua quakes. “Following those earthquakes,” Mr Hayes said, “we felt that it was probable that a further period of comparative quiet might be expected. The present series is possibly due to adjustments taking place in the strata between the centres of the Buller, 1929, and Hawk&’s Bay, 1931, disturbances. “The preliminary investigations of the earthauake which occurred at 7.44 p.m. on Sunday, July 26. show that it was of deepseated origin,” said Mr Hayes, “possibly asdeep as 50 miles or more into the earth’s crust, and its epicentre was at sea near the entrance to Cook Strait, a little to the northeast of Stephen Island. This is, of course, entirely different to the epicentres provisionally assigned to the June 24 and last Sunday’s quakes. The June 24 disturbance was centred in the Masterton area, and Sunday’s shock seems likely to have come from somewhere near the same place. The June 24 quake had its origin close to the earth’s surface, possibly no deeper than about 15 miles down.”