TAUPO QUAKES.

Grey River Argus, 26 June 1922, Page 6

TAUPO QUAKES.

EXPERTS' REPORT. A WATCH WANTED. 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 exjicrts who have returned to Wellington from investigations on the spot. Thev . stale definitely that this is an urgent matter, and recommend the use of seismographs, and the sending of an ob server into the field :.s soon as possible to continue the research work. Pho investigation was conducted by Dr CE. Adams, Government Astronomer and Seismologist; -Mr P- C. Morgan, Direc tor of Geological Survey; and Professor E. Marsden, Professor of Physics, Victoria I'niversity College. Arriving at Wairakei at 4.10 p.m. on June 10, the ])arty commenced the investigation the following day, Dr » Adams : nd Mr Morgan visiting Taupo and the neighbouring localities, and Professor Marsden setting up two rough seismographs. On the 12th the jmrty visited Oruanui, ami on lhe 13th investigated slips at the head of the Wairakei Valley, and later that dry Mr Morgan visited Taupo. The party then broke up, Professor Marsden and Dr Adams returning to Wellington and Mr Morgan proceeding to W aihi. Effect of the Shocks. < On our arrival at Wairrki,” states the report, <f we were informed that a strong earthquake had taken |)lace at 8.16 that morning (Saturday, June 10). This overturned a few bottles in the Bost Office and elsewhere. It was felt northward at Oruanui (where bottles wore also overturned, and a small bust was rotated 45 degrees in a horizontal jdane without being overturned), ami less severely at Mukai. It was also felt at Rotorua, Taumarunui, and at Tarawera. ami on the Napier-I'fiupo Road. At Taupu the shake was not quite so strong. At the Post Office acid was sjtilled from the battery cells, and the clock was stopped. At the Spa Hotel (‘rockery and bottles won' sh: ken off shelves. The apparent greater intensity of the shocks here was probably due 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. “Prior to our arrival, earthquake nctivitv had been experienced at Waiotapu about eight weeks previously for ; about three weeks. The earthquake j origin then apparently travelled south to flu' Taupo Wairakei district. On Frid-y, May 12. a severe and sharp earthquake was f.-’it nt Whakatane, Rotorua, Tauranga, .Matata, and Te Teko at about Hi minutes to 8 p.m. This shake was not reported from T: upo; the first report from the Taupo district was for May Id at G.->8 a.m. Although none of fhe earthquakes was quite of a degree to cause damage to propertv, yet on account of the character of the noises accompanying them and the frcqiiem-y, often 20 in an hour, the inhabitants have become extremely . apprehensive and nervous, (’omlitions were such that visitors refused to stay overnight at tin* Wairakei Hotel, ami both at Wairakei and Oruanui some people had their luggage packed ami doors were left open and arrangements made so that an immediate exodus could take place. The population was particularly afraid of some repetition of the Tarawcra and Waimangu eruptions. The arriv. 1 of our party was appreciated and felt to be opportune. It did much lo reassure the more nervouh of the inhabitants. exjicrimice was as follows: — From 4.40 p.m. on Saturday, June 10, when we arrived, until 6 p.m. there were a dozen easily percejitible shakes, besides minor tremors. At 5.15 p.m. there w; s a strong shock, and at 5.30 p.m. a still stronger shock, during which tlu' whole hotel building (wooden and one storey) 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 ji.m. one observer recorded 19 separate shocks, besides minor tremors, but only two of these were at all sharji. At 7.34 p.m. a single bump was experienced. An Actual Record. “During tin' early hours of Sunday, Juno 11, there were three sharp shocks, and ::t about 7 a.m. another. There were many slight shakes during Sundav, but. none of a severe nature. The following were noted during the afternoon from 12.13 to 4.10 (the figures in parentheses denote the intensity): 12.13 (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, shart. sharp shocks); 4.6 (6), -1.10 , (4.. During t< c evening we noted 11 i At 11.14 p.m. there was a slight shake, slight shocks from 7.23 p.m. to 9.29 p.m. followed quickly by another. About a qu: rtur of an hour later there was a fairlv sharp shock, also followed by a slighter shake. On Monday there was a slight shake at 6.48 a.m., a sharper one at 7.21) a.m., very slight >ics at 7.57 a.m. and 8.571 ran.” Rent Two Miles Long. Having given records of earthquakes at Oruanui, the report proceeds:--‘‘Thu jirevailing surface rocks of the Taupo district are a loosely consolidated pumiccous drift. Owing to its nature, earthquake shocks are felt more easily, especi: Uy in buildings than they would be if solid rock prevailed. Tauhora, east of Taupo, is an andesitic mountain rising to a height of 3603 ft; to the south-west are Tongariro, 6458 ft, Ngaruhoe 7515 ft, and Ruajielm 9175 ft. Sime most earthquakes originate along fault lines, evidence of faulting was sought. Near Taupo, Wairakei, and Oruanui, no direct geological or physiograjdiic evidence of faulting is apparent. but we are informed by Mr Gr: cu, of T.mpo, that a rent had formed during the earthquakes on the western side of the low range went of Taupo, which he considered had 'a length of two miles. (This rent is thus on the main fault line —White Island, Tarawera, Ruapehu). “On the west side of this the ground h: d fallen a foot, or else the oast side had risen a similar amount. The vent, he stated, trends north and south. We think that perhaps it strikes a little east of north. In all probability this earth-crack indicates a fault in the more solid jocks at some depth in the errth’s crust. The pumice drifts are almost too loosely considated 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 the earthquake origins, for there are ties were overthrown. Only two little slips were seen on the Oruanui-Taupo

several. Another method was used to estimate the approximate origin ut the earthquakes. The telephone was connected with observers at Wairakei, Taupo, Oruanui, and Mukai. The same shock was observed at the different places, and an indication given by word of month. Most shocks were practically simultaneously felt at Wairakei, Taupo, and Oruayui, and two seconds later :.t Mokai. As the earthquake waves travel about two miles and a-haif per second, the observations showed that the centre of the disturbance was in the triangle formed by Wairakei, Taupo, ami Oruanui. Moreover, ih«? intensity at Mokai was less than at the three other places. Again, by comparison of intensities of shocks at th*? different places, it was clearly shown that the (<igin of the earthquakes was not a fixed locality. In particular, it moved north on Monday night, and returned southward on Tuesday moruillg\ ‘‘This evidence was also in complete agreement with the relative magnitudes of the north-south and east-west com- I ponents on the seismograph records. I The seismographs were imjirovised ones I recording on sheets of smoked glass, I which were moved by the sinking of ■ wooden floats in leaking kerosene tins. ■ It is very unfortunate that butter seis I mograjdis ami recording devices were | not available, as more exact location I of the origins, including the depths ( below the surface, could have been | hoped for. j Volcanic Action, “We considered whether volcanic action, such as moving lava or the foundering of the roofs of caverns vacated by lava, was possible, and came to the conclusion th: t such an origin may probably be discarded. The hot springs, ( steam vents, etc., at Wairakei, Taupo, and elsewhere were quite normal before : and during our visit. Ngaruhoe was ' almost quiescent, with only a slight steam column from the crater, and Te M: r:ic appeared to be the same as usual. Tho surface effects of the earthquake appeared to be very slight. A few* botRoad near the 4S-mile post. A small slip was also seen up the Wairakei Gey ser Valley. “The shocks are too numerous to record in full, and, with few exceptions, ■ re not severe. The probability is that the frequent small shocks relieve the strain gradually, and are therefore preferable to a large earthquake. Consid- i crable alarm, however, is caused by the [

| large number of shocks, which produce ■ a uumuk tivu effect on the inhabitants. Urgent Recommendation. ’’Fiie situation is such that a close watch must be kept on the earthquake? in the district ami the migration of their centres. This is urgent matter, I and we recommend that seismographs, be made to register the three components. north-south, oast-west, and vertic: 1; ami that an observer be sent into the fieljl as soon as possible to continue tiie investigation on the lines of this report, and to make as eyuuratc records of the earthquake centres ns possible. When the evidence of the temporary observer is available, we d<*sire to submit an additional recommendation for* turf her observation in ibis region.