Highlights of 30 years of strong-motion recording in New Zealand
Cousins, W. J.
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Strong-motion recording has been carried out in New Zealand for somewhat more than 30 years. The largest network of instruments, comprising 220 accelerographs and 72 scratch-plate acceleroscopes, is operated by the Institute of Geological and Nuclear Sciences. During the last 30 years the IGNS network has yielded a little over 2000 records, 1600 of which have been matched with earthquake events to give a substantial body of New Zealand data that is currently being used in studies of attenuation and microzonation. The highest peak ground accelerations recorded to date on scratch-plates and accelerographs are respectively 0.6g (from Reefton during the 1968 Inangahua earthquake) and 0.4g (from Dannevirke from the Weber earthquake of 13th May 1990). About 300 of the more significant accelerograms have been digitized and computer processed to give data sets suitable for use in aseismic structural design, and studies of the attenuation of spectral acceleration, soil-structure interactions, structural responses, and microzonation. Peak ground accelerations from New Zealand earthquakes appear to be stronger, over a wide range of source distances, than predicted from attenuation models applicable to the Western USA. Spectral accelerations in New Zealand appear to modelled well by a model based on Japanese data, but some caution is needed as the New Zealand data base of spectral accelerations is small and deficient in near source data from moderate to large earthquakes. Strong-motion records from deep or soft soil sites, and from arrays of recorders in the Wellington region, have shown both resonant and broad-band amplification for rock input motions of small to moderate intensity. Sets of records from arrays of accelerographs in three medium-rise buildings have revealed the effects of soil-structure interactions, and records from an array of 5 accelerographs on Matahina dam showed that part of the dam responded in a strongly nonlinear fashion during the 1987 Edgecumbe earthquake.