EARTHQUAKES’ ORIGIN.

Taranaki Daily News, 22 July 1922, Page 10

EARTHQUAKES’ ORIGIN.

INVESTIGATIONS AT TAUPO. DISTURBANCES DEEP DOWN. (SITUATION NOT ALARMING. The results of hie observations at Taupo were outlined in an interview by Professor Marsden, of Victoria College. Professor Marsden on his second visit to the Taupo district, took with .him a full set of speciallyconstructed seismographs. He arrived at Taupo just in time to- experience the week-end series of earthquakes, although he was not able to set up the whole of the setemographs until the series was nearing its end. He has left an observer, Mr. M.- N. Rogers, and a volunteer local observer, Mr. Stenberg, to continue taking records. Professor Marsden said the seismographs worked well and produced a large number of records from which fairly reliable conclusions can be drawn. The main point in the results is that the origins of the disturbances have been located as lying beneath the uninhabited area westward and north westward of Taupo and at a depth of roughly three miles. There is still not enough evidence to show ■whether or not there is a prospect of a dangerous upheaval, but the situation cannot be said to foe in any way alarming. The seimographs used gave records of both horizontal and vertical components, and the records from the vertical seismograph gave particularly interesting results. Professor Marsden stated that he considered the fissures at Oruanui and a few other places were relatively unimportant as danger signs, as they were in loose alluvial soil which yielded easily to the shaking stresses of an earthquake.

CONTINUITY OF SHAKES. Commenting on the cartbqv-.kes generally, Professor Marsden said that their most notable feature is not their great violence or the damage caused, but the continuity of the series and the recurrence of series after series. A number of slips of earth have occurred, but certainly not more than one would expect after experiencing the shocks. In fact it is surprising to see on a trip through the country how few there have been. A few chimneys are cracked, but only one or two old ones have fallen, and the principal damage has been due to the falling of loose objects. The shelves in the hotel bars at Taupo and Wairakei were, perhaps, injudiciously left filled with bottles and the earthquakes cleared them all off.

The successive series of shakes have occurred at intervals of six days or so, and it was a remarakble fact that so far the outbursts had been getting shorter but the individual shocks rather more severe. The week-end experience was notable for the frequency of shocks within a short period. Between 1 a.m. and 9 a.m. on one Sunday Mr. Hughes, a surveyor, who was in the district, counted 57 distinct shocks.

NERVE-RACKING EXPERIENCE. From information he had received in Taupo and Oruanui the earthquakes on the previous Sunday must have given the people a very nerve-racking time, for the ground seemed at times to be continually in motion, with a definite upward bumping. All the Maoris left Oruanui that day. They were returning on the Monday, eight days later, preparatory to a feast on the following day. The personal effect of earthquakes is much the same anywhere, and Professor Marsden, instead of giving a firsthand description, quoted from Dr. C. Davidson's “Manual of Seismology” as follows: —“The first sign of an earthquake is usually a low rumbling sound, so low that to some observers not otherwise deaf it is quite inaudible. The sound grows gradually louder, and with it there become susceptible faint but rapid tremors like those experienced during the passage of a heavy train or waggon, about four or five tremors occurring to the second. They merge more or less rapidly into vibrations of considerable range and duration, not more than two or three per second, while in strong earthquakes each vibration may last a second or even more. Except in great earthquakes, when once the maximum is reached, the vibration and sound usually decreased in strength, the shock sometimes ending with a tremulous motion. In very slight earthquakes the principal portion may be absent, and a weak tremor may alone be felt. In some slight earthquakes the preliminary or concluding tremors may be omitted, usually the former, in which case the sensible shock begins with a single prominent vibration like the thud of a falling body followed by brief tremors such as a fall would produce in a building.”

SOUND PHENOMENA. This description, he said, fitted the Taupo earthquakes exactly. The sound phenomena were particularly interesting owing to the lowness of the note. It often happened that out of a party of five, or six two would suddenly say they “heard one coming,” while the others (including himself) remained quite insensible to the sound. A second or two later they would all feel the shake. Some of the noises, particularly the higher notes which closely resembled the sound of gunfire, were declared by many observers to seem to come from , the air, but the deeper rumblings sound|cd as if they were in the ground. Often the booming occurred without any sen- ' sible shock. The general thermal activity in the ; district has certainly not become less J than usual. If anything it is slightly l greater. One or two new steam holes have been reported, but the various i “attractions” are carrying on their busi- [ ness as usual regardless alike of earthquakes and fewness of visitors. The , people of the district naturally presented an interesting psychological study. Continued experience of the earthquakes has had a cumulative nervous effect upon some of them, and gen-

orally they have become remarkably sensitive to shocks that newcomers are •unable to detect. That is a common experience in earthquake districts. I Professor Marsden remarked that the residents, surrounded year after year by the evidences of the tremendous forces of nature, do not exemplify the proverb that familiarity breeds contempt. On the contrary, they realise much more fully than the visitors the significance o-f thermal action. The tourist has rather the attitude of one for whose benefit the steam is turned on and off by a hidden stage manager. The residents have a fine respect for the enormous output of energy, apparently per-

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