“NORMAL TWITCH”

Wairarapa Times-Age, 4 July 1942, Page 3

“NORMAL TWITCH”

IN GROWING PAINS OF NEW ZEALAND GEOLOGISTS REPORT ON EARTHQUAKE NEED OF BETTER BUILDING STANDARDS. AS SAFEGUARD AGAINST CASUALTIES. (By Telegraph—Press Association.) WELLINGTON, This Day. The earthquake that shook the Wairarapa and other parts of New Zealand on June 24 is shown by an examination of the country to have been most intense along the fault line running through Bideford, Taueru. Gladstone, and east of Lake Wairarapa, state Mr Al, Ongley and Dr. A. R. Little, of the Geological Survey Office, reporting on a visit to the Wairarapa district.

They also say that the occurrence could not be regarded as exceptional, as it was a normal twitch in the growing pains of New Zealand, and would be followed periodically by more, with the result that the attitude of the public and local bodies must become less complacent. A large part of the population must learn to regard the earthquake as belonging to their environment, and in preparing to cope with it, as with bad weather and fires, they must build houses*accordingly. MANY EARTHQUAKE FAULTS. Explaining the cause of earthquakes they state that all countries bordering the Pacific are under stress between the heavy bottom of the ocean and the light rim of land enclosing it; these stresses are relieved periodically by land breaking and moving alone a plane of weakness. In this way earthquakes are generated, and the planes of weakness .along which the land breaks and moves, are called faults. In New Zealand, perhaps, the best known of these faults is the Rimutaka fault, separating the Rimutaka-Tararua range from the Wairarapa lowland, because it was along this fault that the land moved in the 1855 Wellington earthquake. This fault is only one of the many that traverse New Zealand, and are so numerous that a map of .fault has to be shown on a large scale to enable the separate ones to be shown. As New Zealand is being examined, more and more faults are being detected; and miners, engineers and geologists are constantly dealing with faults and fault-problems. Not all the faults have been active in historical time; and the minority of faults, the active ones, are the special problem of the seismologist. LINE OF RECENT SHAKE.

The recent earthquake had been commonly blamed on to the Rimutaka fault, but an examination of the country showed that the damage to the ground was distributed symmetrically along a line running parallel with the Rimutaka fault but 10 miles east of it. It could appropriately be called the Taueru fault, for it ran along the Taueru Valley for many miles. The damage increased toward this belt on both sides symmetrically; along it the damage was most intense; and along it two miles north of Taueru at the Mangatopitopi the fault broke through the soil and turf to the surface for half a mile.

GOOD & BAD FOUNDATIONS,

In many cases houses built on silts and filled ground suffered considerably more than those built on solid strata. In the Longbush region it was noticeable that at least one house built on limestone stratum was completely unscathed, while all houses on the alluvials were damaged. Where convenient, prospective builders should investigate the nature of alternative sites more thoroughly. It should not, however, be inferred that construction on alluvials was necessarily bad. On the contrary well-built structures of monolithic design built on gravel were recommended by competent authorities, since the gravel absorbed much of the shock. The foundation of the house in such cases should be in the nature of a raft, with the upper structure very securely tied to it.

Insufficient attachment to foundations appeared to be a common fault. In several cases houses had been thrust off their foundations and rotated. If attachment had been sufficient the houses would have probably suffered much less damage, it was stated. The most dangerous structures in the towns were those erected for ornamental purposes. Ornamental parapets of bad design and questionable material over shop fronts had fallen, frequently leaving the sound and sensible underlying structures untouched. A general pruning of such unnecessary and potential missiles, even where they had not already fallen, was desirable. DESIGN OF CHIMNEYS. The most widespread damage was to chimneys. Thousands of chimneys had fallen, and it was doubtful if many of these were constructed with good mortar; the design was certainly bad. It was notable that the State houses were quite undamaged in Masterton,, as well as at several other towns, proving that good chimney designs existed, and it was desirable that the reconstruction of fallen chimneys should follow sound specifications. Unfortunately, many individuals were already re-erecting chimneys on the stumps of the old ones, and the rebuilt chimneys were likely to be. as bad or worse than their predecessors. An admirable opportunity for building reform would be lost if such haphazard reconstruction continued. The attitude of the public and local bodies in general toward earthquakes should be less complacent, because if the recent earthquake had taken place during a busy shopping period, it could well have caused in Masterton alone some 200 to 300 casualties, which would have been all avoidable with good design and good materials. A large part of country particularly liable to earthquake shocks could certainly be more adequately defined by the seismologist now than previously; it embraced the whole of the Hawke’s Bay and Wairarapa region, as well as Wellington city and its environs. All constructional work should be undertaken with the view that it would certainly have, to withstand earthquake shock sooner or later. Good specifications had been drawn up by the New Zealand Standards Institute to cope with the earthquake dan-

ger, and their rigorous enforcement was essential. Where the design and construction was conscientious, and where all the principal building matrials were good, namely, good wood, concrete, and brick, adequately reinforced, the difference in cost between a properly built structure and an unsafe one was only about 10 per cent. The alternative to building larger structures according to a strict code was to build small wooden houses with a very light external chimney and light furniture.