Earthquake Zoning For N.Z. “Ignores Agadir”

Press, Volume CII, Issue 30288, 14 November 1963, Page 3

Earthquake Zoning For N.Z. “Ignores Agadir”

To allow inferior standards in earthquake building codes in certain zones of New Zealand would be to “ignore the plain lessons of Agadir, Lar, and Skopke,” says Dr. F. F. Evison. superintendent of the Seismological Observatory, Department of Scientific and Industrial Research, writing in “New Zealand Engineering.” These three places, at each of which severe earthquakes have occurred during the last few years, are all in regions where the seismic activity is much less than in New Zealand, Dr. Evison says. Dr. Evison was contributing to a discussion on “Lessons from Agadir” started by Mr R, J- P. Garden, a Dunedin consulting engineer, in an earlier issue of the journal Mr Garden, who is a member of the committee for earthquake engineering of the New Zealand Institution of Engineers, said that New Zealand proponents of seismic zoning “would certainly have rated Agadir as bearing a substantial earthquake risk,” because it was destroyed by an earthquake in 1731, in a region where active moun-tain-building persisted, and on the Alpide earthquake belt. There were many geological faults in the area, and 15 earthquakes of over force 5 on the Richter scale had been recorded in the neighbourhood in a 17-year period. One of the main causes of the severe loss of life (16,000 persons were killed) at Agadir was the lack of an earthquake building code, Mr Ger. den said. “Neither Sodom nor Gomorrah did more to invite destruction” than the builders of Agadir. Mr Garden thought New Zealand proposals paid in-

sufficient attention to the possibility of a sudden one-way movement of the ground, as had apparently occurred at Agadir, and "during other earthquakes. The current code was based on the concept of a vibratory motion, he said. Dr. Evison said if Agadir qualified for a high rating on the scale ot earthquake design. so did the whole of New Zealand. The earlier earthquake at Agadir was in prehistory as far as New Zealand was concerned, and noone knew what earthquakes had occurred in past times on the sites of New Zealand cities. During the same period that the “neighbourhood' ’ of Agadir quoted by Mr Garden (in fact, the territory of Morocco) had its 15 earthquakes over force 5, New Zealand, with two-thirds the area, had had 154 shocks of the same force or greaterThe circum-Pacific earthquake belt on which New’ Zealand lay was much more active than the Alpide belt. Dr. Evison said. “'Hie (seismic) zoning principle has recently been abandoned after 12 years’ trial, by the structural engineers of California, where earthquakes of damaging in•.ensity are about as frequent as they are in New Zealand. “No-one would suggest that any but the highest standards of earthquake design should be adopted in those extensive areas of. New Zealand where large earthquakes have already occurred in the brief time covered by the seismological record. To allow inferior standards in the other areas would be to ignore the plain lessons of Agadir. Lar, and Skopje,” he said.