TAUPO EARTHQUAKES.

New Zealand Herald, Volume LX, Issue 18471, 7 August 1923, Page 8

TAUPO EARTHQUAKES.

REPORT BY GEOLOGIST.

SUBSIDENCE ,OF LAND. ■ [Br TEtEGBAtH. — BEPORTEB.J WELLINGTON. Monday. Reference .to the earthquakes in the Taupo district last year-is mad© (Dr.. P. G. Morgan, Director -■;; of Geological Survey, in hi 3 report presented in ( the House of ;; Representatives : tO*dfty.;,Tho material damage done; by the TaupO earthquakes, : ho says,. was ■ confined .to , the shaking i down cof several ■ ; chimneys at Oruanui and to the breaking of articles such as crockery and bottles which were shaken off shelves. Somewhat numerous though, as- ' a rule, small slips occurred ■"along.. 1 -.-roads' and elsewhere, especially along the north shore of Lake Taupo.; ,v'-,; The * most remarkable feature, however, was the subsidence of a considerable block of land on the north side, of..Lake Taupo between Whakaipo and ■ Whangamata' Bays. The drop at'- the ; beginning of ;!• September was Ah. ft. near the south end of the peninsula between these bays. During-j the following .-■'• months the subsidence increased and has lately been reported :as 7Aft.' Northward it gradually diminished. * Its eastern boundary was probably a large crack or series of cracks seen early in June to the north-east of Whakaipo Bay. On the western, side of this a drop'averaging 18in. was observed. The number of shocks, great and small, comprising the Taupo /' swarm " was very large and probably has seldom been ! equalled .in earthquake records; The | loose, unconsolidated! nature of, the surface rocks and perhaps the weakness of the- deeper seated rocks : were -probably contributing factors to this distribution of the seismic energy. The shocks were undoubtedly of: a .Tectonic',;- nature and ,-. had their origins along: 'a : north-north-east striking fault : zone, & few , miles to the west 7 of Taupo township and Wairakei. They were not '" volcanic," nor directly j due to; movements of . magma in?subterranean reservoirs. . Gentle movements along \ this fault seem to have begun near Waiotapu in _ April. [ During May centres of activity : migrated to the neighbourhood of Oruanui,- j Wairakei, and Taupo township. Early in Sep- | tember there were movements near Tokaanu; also many earthquakes occurred in neighbouring districts. During the time of activity in the Taupo district shakes were felt in the Te Awamutu district,l over 60 miles north-west of Taupo, during June and other months, and one was recorded at , Hamilton, about 15 miles north of Te Awamutu, on October 15. Several sharp shocks were felt at Ohakune on September 3 at a time when numerous tremors were being experienced at Tokaanu, 37 miles to the northeast. About "midnight on ; October '12 a " heavy shock " was .felt. at Taumarunui, 35 miles west-south-west from Taupo, and many " distinct " tremors followed during the next few hours. During the previous three weeks or move many light shocks had been felt. The Ohakune shakes no doubt had an origin in the Taupo fault zone. Those in the Te Awamutu, Hamilton, and TaumarUnui districts seem to have had independent origins.