EARTHQUAKE RISK IN NEW ZEALAND

Dominion, Volume 37, Issue 188, 8 May 1944, Page 4

EARTHQUAKE RISK IN NEW ZEALAND

Evidence Reviewed PRECAUTIONARY METHODS ADVOCATED Earthquake risks in New Zealand, possible methods of approach to the problem of earthquake prediction and suggestions for minimizing damage, are discussed in a recently-published paper by the director of the geological survey branch of the Department of Scientific and Industrial Research, Dr. J. Henderson. "Our geology, our land forms and our history,” he says, “remind us that earthquakes are part of our environment. The risk of earthquake damage is more general and widespread than most people realize, but is far less. than that of motor accidents or of infectious diseases, lhe effects can be tempered, by suitable and not too onerous precautions. “Seeing that at least 73 earthquakes strong enough to topple over chimneys and shop-fronts have occurred in New Zealand in 142 years, an earthquake of destructive or near-destructive violence takes place on an average each two years. Indeed, during the last 20 years the average has been more than one eacli year. ...” . .. After referring to accounts of earthquakes felt since European occupation, Dr. Henderson sketches the topographical and geological evidences of still earlier upheavals. The historical record he says, covers less than 150 years, and owing to the sparseness of population in some districts before 1860, is incomplete even for strong shocks. It gives, however, some idea of the area of New Zealand known to have been strongly shaken. “This known strongly-shaken area will undoubtedly be extended as the years pass, for the whole of New Zealand is within, or uncomfortably near the ‘mobile belt’ bordering the Pacific, he adds. ... "The risk is general and widespread; but some parts are known to have been shaken more strongly and more often than others, and some parts have not been strongly moved since the coming of Europeans. With the present, incomplete data the degree of liability to damage of any particular district cannot be accurately assessed. No one can tell when the next destructive earthquake will occur, where its focus will be, or how great will be its energy.” Most Vulnerable Districts. After discussing various districts in detail he says: “From the historical records and the evidence of known fault traces, the Hawke’s Bay-Wellington-Marlborough region is the most liable to earthquakes in New Zealand. Next follows a group of areas made up of Roto-rua-Taupo, Wanganui-Nelson, West Nelson and West Otago, in each of which major shocks have been recorded, but in which, except for the fissures continuing the Tarawera-Rotomahana rifi, few earth rents are known. The third group contains Raukumara and HaurakiTaranaki areas, which experience occasional heavy shocks, though none of major violence ,has occurred within the last century.' Canterbury, which constitutes the fourth subdivision, shows a few surface traces; the damaging shocks so far recorded seem to have been from or near the sensitive northern margin. The fifth group consists of East Otago and North Auckland, in which the few light shocks have probably originated in other districts.”

After pointing out that eo far it has been impossible to predict the accurate locating, or approximate time of a shock. Dr. Henderson says that quite a different thing from precise prediction, or rather prophecy, not based on verifiable evidence, is information about slow secular movements of the ground and about stress conditions prevailing in the rocks of any region. For, in a district subject to strong earthquakes even at long intervals, sure methods of knowing that stresses in the earth crust were building up to a dangerous point would be of great value to authorities, not for broadcasting, but for making preparations aud taking precautions. Such determinations, might be possible. •Since earthquakes cannot be prevented or controlled, says Dr. Henderson, other means of reducing the risk must be tried. He advocates a suitable building code, applying to the whole of the Dominion, with the difference in hazard, according to district and foundation ground, allowed for in insurance rates. Stating that earthquake behaviour, subjacent conditions and shock-resistant design are not yet fully understood, he also urges that great conurbations or, in a large city, a concentration of public amenities, should not be encouraged.