EARTHQUAKE SHOCKS

Otago Daily Times, Issue 23688, 21 December 1938, Page 19

EARTHQUAKE SHOCKS

NEW ZEALAND VISITATIONS SHAKES PROBABLY RELATED OFFICIAL SEISMOLOGICAL REPORT (Per United Press Association) WELLINGTON. Dec. 20. The proximity in time and of the areas affected by last Thursday night’s earthquake over the southern portion of the North Island and that over a wide area of the south of the South Island on Saturday morning suggest strongly that the two movements were closely related, though the exact relationship has not yet been established by seismologists. The acting-director of the Dominion Seismological Observatory at Wellington. Mr R. C. Hayes, said to-day that the reports he had received indicated that the South Island earthquake had been felt as far north as Westport and Murchison on the West Coast and to Akaroa on the east coast. The North Island shake had been reported from Whakatane on the east coast and New Plymouth on the west and down to Blenheim and Nelson on the South Island. It had also been recorded slightly at Akaroa and the Chatham Islands. The seismograph records showed the centre of the shake to be in the region of Porongohau and Waipukurau, in both of which places its intensity was recorded at eight on the Rossi-Forel scale. The average intensity in Wellington was three on the scale. In some parts of the city it may have been four and in others less than three, which account for the fact that many Wellington people did not feel the shake. There had been a few aftershocks from the North Island earthquake, Mr Hayes said. Dannevirke had reported two small after-shocks, one at 1.56 p.m. on Friday and the other at 8.56 a.m. on Sunday. After the South Island shake there were a large number of after-shocks. A heavy one occurred at about 11 a.m. on Saturday, and it was followed by a number of others which were all much smaller, but they seemed to have ceased now.

The South Island earthquake was centred near the coast between Milford Sound and Doubtful Sound. At Queenstown, it registered over seven on the Rossi-Forel scale. That is the highest intensity recorded so far as is known. In Wellington, at present, reports are still to come to hand from reporters at Milford Sound and Jackson’s Bay. The intensity of the shake, however, was six over a large part of Otago and Southland, where it was quite widely distributed. The Dominion Seismological Observatory has about 25 reporting stations in that area, so that very complete information on the course of the movement and its intensity will be available when all the information has been received The only seismograph station in the area is at Lake Monowai, and its record has not yet been received. Possibly the two earthquakes were related, Mr Hayes said, but he would not like yet to say how One large shake nearly always distributed regions around the area in which it was felt, and thus was liable to set off other earthquakes sooner than they were liable to happen otherwise. A shake was recorded near Wanganui on November 23, and might quite reasonably have had something to do with the one which followed on Thursday over the south of the island. There had also been a small shock at Monowai before the South Island shake, and it was probably connected with the latter. “ You do get foreshocks of earthquakes, but one cannot tell they are foreshocks till afterward." Mr Hayes said. Mr Hayes said that on an average over "a long period there were slightly more earthquakes in winter than in the summer in New Zealand, but the excess was very slight, almost too slight to have any significance. The distribution of earthquakes between winter and summer was not regular from year to year. The centre of the South Island shake is subject to revision when more complete details are available from the reporting stations. It was well recorded on the seismographs of the Dominion Observatory at Wellington, which is approximately 470 miles from the centre which has been fixed on the earliest information available. Big earthquakes in the south of the South Island are infreauent, and Saturday’s was the strongest recorded in that region for some time There has been nothing reallv big there since the days of European settlement, though there are stories of very heavy shakes in the Dusky Sound area when there were only sealers there.