Forecast Of Earthquake Incidence Criticised

Press, Volume CI, Issue 29718, 11 January 1962, Page 8

Forecast Of Earthquake Incidence Criticised

A prediction as to how often major earthquakes may be expected in the main centres, made by Mr R. Gordon in Dunedin, has been criticised by Dr. F. F. Evison, of Wellington, superintendent of the Seismological Observatory of the Department of Scientific and Industrial Research.

“The newspapers of January 9 reported from Dunedin a statement about earthquake risk in Auckland, Wellington. Christchurch, and Dunedin, attributed to a Mr R. Gordon, an engineering geologist,” said Dr. Evison yesterday. “I have not had the opportunity of studying the details of Mr Gordon’s arguments, but I can say that what we know about past earthquakes in New Zealand gives no basis for his conclusions. “Since European settlement, there have been 15 major earthquakes in New Zealand—that is, earthquakes of magnitude sever or greater on the Richter scale. These have been widely, if not uniformly, distributed between the Bay of Plenty ahd southern Fiordland. They do not constitute evidence from which one could make numerical estimates of the incidence of future earth- . quakes. ’

“The reported statement specify! .g the risk to Wellington city of destruction by earthquakes is of a kind that should be discouraged unless it can be fully backs. ’ by scientific evidence. It is all too easy to issue this sort of prognostication, and it is sometimes done in the mistaken belief that the public interest is being served thereby. Actually, the effect can be harmful, because not only are people upset without cause, but a balanced and well-founded view becomes more difficult to establish.

“The statement repeats the dubious estimate that ‘they have a major earthquake every 80 years in Wellington’. This estimate, which was first publicised some years-ago, is derived' from observations of geological faults, and relies on the assumption that all past fault movement is evidence of earthquakes. This assumption is now known to be untenable, for it has been discovered that movements, even on large faults, can occur from gradual creep without any accompanying earthquake activity. "The historical record of major earthquake activity in Nevi Zealand is too brief to support estimates about relative risk in different areas. The most promising way of increasing our information appears to be that of studying every earthquake that occurs in New Zealand, down to quite small magnitudes. It is hoped in the next few years to improve the New Zealand network of seismograph stations so that adequate coverage for this purpose will be achieved.”