WATCH NEEDED

Evening Post, Volume CIII, Issue 141, 17 June 1922, Page 6

WATCH NEEDED

TAUPO EARTHQUAKES

REPORT OF THE EXPERTS

NECESSITY FOR OBSERVER STRONGLY URGED.

That a close watch must be kept on the earthquakes in the Taupo district and on the migration of their centres, is the conclusion reached by the experts who have just returned from investigations on the spot. They state definitely, that this is an urgent matter, and recommend the use of seismographs, and the sending of an observer into the field as soon as possible to continue the investigation. The investigation was conducted by Dr. C. E. Adams, Government astronomer and seismologist; Mr. P. C. Morgan, Director of Geological Survey; and Professor E. Maradon, Professor of Physics, Victoria University College.

'Arriving at Wairakei at 4.10 p.m. on 10th June, the party commenced the investigation the following day, Dr. Adams and Mr. Morgan visiting Taupo and the neighbouring localities, and Professor Marsden setting up two rough seismographs. On the 12th the party visited Oruanni, and, on the 13th investigated slips at the head of the Wairakei Valley, and later that day Mr. .Morgan visited Taupo. The party then broke up, Profeseor M&rsclen and Dr. Adams returning to Wellington and Mr. Morgan proceeding to Waihi. EFFECT OF THE SHOCKS. "On our arrival at Wairakei," states the report, "we were informed that' n strong earthquake had taken place at 8.16 a.m. that morning (Saturday, 10th. June). Tliis overturned a few bottles in the Post Office and elsewhere. It was felt northward at Orunui (where bottles were also overturned, and a small bust was rotated 45 degrees in a horizontal plane without being overturned), and'less severely at Mokai. It was also felt at Eotorua, Taumnrimui, and at Tarawera., and on tho Napier-Taupo-road. At Taupo the shake was not_ quite so strong. At the Post Office acid was spilled from the, battery celte, and ;the clock was stopped./ At the Spa Hotel crockery and bottles were shaken off shelves. The apparent greater intensity of the chocks here was probably doio to the looser formation of the ground. At the Terraces Hotel the shock was not so -severe—no bottles were shaken off the shelves. On the whole, this appears to have been the strongest of the shakes up to the time of writing this report. TWENTY AN HOUR. "P.riof .to our arrival, earthquake activity... had been experienced at Waiotapu about eight weeks previously for about three weeks. The earthquake origin then apparently travelled south to the Taupo-Wairakei district. On Friday, 12th May, a severe and sharp earthquake was felt at Whakatane, Rotorua, Tauranga, Matata, and Te Teko at about 10 minutes to 8 p.m. This shake was not reported from Taupo; the first report from the Taupo district was for 10th May at 6.58 a.m. Although none of the earthquakes were quite of a degree to cause damage to property, yet, on account of the character of the noises .accompanying them and the frequency, often 20 in an hour, the inhabitants have become extremely apprehensive and nervous. Conditions were such that visitors refused to stay overnight at the Wairakei Hotel, and both a-t Wairakei and Oruanui: some people had their luggage packed and doors were left open and arrangements inacTe so that an immediate exodus could take place. The population was particularly afraid of some repetition of the Tarawera and Waimangu eruptions. ' The arrival of our party was appreciated and felt to be opportune. It did much to reassure the more nervous of the inhabitants. "Our experience was as follows:— From 4.40 p.m. on Saturday, 10th June, when we arrivedj until 6 p.m. there were a dozen easily perceptible shakes, besides minor tremors. At 5.15 p.m. there was a strong shock, and at 5.30 p.m. a still stronger shock, during which the whole hotel building (wooden and one story) shook violently; the wall of the smoking-room vibrating perceptibly. After this the shakes were fewer and- milder. However, from 7.21 p.m. to 8.40 p.m. one observer recorded 19 separate shocks, besides minor tremors,, but only two of these were at all sharp. At 7.34 p.m. a single- bump was experienced. AN ACTUAL RECORD. "During the early hours of Sunday, 11th June, there were three sharp shocks, and at about 7 a.m. another. There were many slight shakes during Sunday, but none of a severe nature. ■The following were noted during the afternoon from 12.13 to 4.10 ' (the figures in brackets denote the intensity:—l2.l3 (4); 12.15 and 12.16 (5); 12.20 (4); 12.23 (3); 12.46 (7, sudden sharp shocks from the north); 12.47 (2); 1 o'clock (2); 1.53 (2, lasted one minute); 1.56 (3);.1.58 (4); 2.1 (4); 2.26 (3); 3.46 (5-6, short, sharp shocks); 4.6 (6); 4.10 (4). During the evening we noted eleven slight shocks from 7.23 p.m. to 9.29 p.m. At 11.14 p.m. there was a slight shake, followed quickly by another. About a quarter of an hour later there was a fairly sharp shock, also followed by a slighter shake. On Monday there- was a slight shake at 6.48 a.m., a sharper one at 7.20 a.m., very slight ones at 7.57 a.m. and 8.57J a.m." RENT TWO MILES LONG. Having given records of earthquakes at Oruanui, the report proceeds:— "The prevailing ' surface rocks of the Taupo district are a loosely consolidated pumiceous drift. Owing to its nature, earthquake shocks are felt more easily, especially in buildings, than they would be if solid Tock prevailed. Tauhora, east of Taupo, is an andesitic mountain j rising to a height of 3603 ft; to the j south-west are Tongoriro, 64581't, Ngau, ruhoe 7515 ft, and Ruapehu 9175 ft. Since most earthquakes originate along fault lines, evidence of faulting was , sought. Near Taupo, Wairakei, and I Oruanui, no direct geological or physiographic evidence of faulting ia apparent, \ but we are informed by Mr. Grace, of Taupo, that a rent had formed during j the earthquakes on the western side of the low range west of Taupo, which he considered had a length of two miles. J (This rent is thus on the main fault line—White Island, Tarawera, Euapolm). " On the west side of this the ground ! had fallen a foot, or else the, cast side lincl risen a similar amount. The rent, • bo stated, trends north and south. We think that perhaps it strikes a little east of north. Ia all probability this earth-crack indicates a Fault in the more solid rocks at some depth in the earth's crust. The pumice drifts are almost too Joosely consolidated to allow well-marked faults to form in them. NOT A FIXED ORIGIN. " The seismograph records, detailed later, rough as they are, point clearly to a fault plane some miles west of Taupo and Wairakei, as the locus of Hie : earthquake origins, for there are several. Another method was userl to estimate the approximate origin of Iho earthquakes.. The telephone .was connected

with' observers at Wairakei, Taupo, Oruanui, and Mokai. The same shock was observed at the different places, and an indication given by word of mouth. Most shocks were practically simultaneously felt at Wairakai, Taupo, and Oruanui, and two seconds later at Mokai. As the earthquake waves travel about I two miles and a-half per second, the observations showed that the centre of the disturbance was in the triangle formed by Wairakai, Taupo, and Orua- ' nui. Moreover, the intensity at Mokai j was less than at the three other places. I Again, by comparison of intensities of ; shocks at the different places, it was I j clearly shown that the "origin of the | earthquakes was not a fixed locality. In particular, it moved north on Monday night, and returned southward on Tuesday morning. " This evidence was also in .complete agreement with the relative magnitudes I of the north-south and east-west com- j ponents on the seismograph records, i The seismographs were improvised ones recording on sheets oE smoked glass, which were moved by the sinking of wooden floats in leaking kerosene tins. It is very unfortunate that better seismographs' and recording devices were not available, as more exact location of the origins,- including the depths below the surface, could have been hoped for. VOLCANIC ACTION. "We considered whether volcanic action, such as moving lava or the fowMrering of the roofs of caverns vacated by lava, was possible, and camo to the- conclusion that such an origin may probably be discarded. The. hot springe, steam vents, etc., at Wairakei, Taupo, or elsewhere were quite normal before and during our visit. Ngauruhoe was almost quiescent, with only a slight, steam column from the crater, and Te Marae appeared to be the same as usual. j The surface effects of the earthquake | appeared to be very slight. A few j bottles were overthrown. Only two little I slips were seen on the Oruanui-Taupo-j road near the 48-mile post. A smalt I slip wag also seen up the Wairakei .Geyser valley. "The shocks are too numerous to record in full, and, with few exceptions, are not severe. The probability is that the frequent small shocks relieve the strain gradually, 'and are therefore preferable to a large earthquake. Considerable alarm, however, is caused by the large number of shocks, which produce a cumulative effect on the inhabitants. ■ URGENT RECOMMENDATION. "The situation is such that a close watch must be kept on the earthquakes in the district and the migration of their centres. This is urgent matter, and we recommend that seismographs be made to register the three components, north-sonth, east-west, and vertical; and that an observer be sent into the field as soon as possible to continue the investigation on the lines of this report, and to make as accurate records of the earthquake centres as possible. When the evidence of the temporary observer is available, we desire to submit a further i-ecommendatiqn for the further observation in this-region."