Microseismic noise survey of Dunedin City

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Adams, R.D.; Kean, R.J. 1974 Microseismic noise survey of Dunedin City. [s.l.]: [s.n.]. Report / Geophysics Division 97 10 p.

Abstract: Following the damaging earthquake near Dunedin on 9 April 1974 (magnitude 5.0), a microseismic noise survey was undertaken to compare the variation of the amplitude of natural ground noise with the pattern of damage. Measurements were made in three frequency bands at 67 sites. Alluvial areas in the south of Dunedin, where the damage was heaviest, generally showed higher levels of ground noise. This effect was particularly marked in the frequency band 5 to 8 Hz, for which the amplitudes on the alluvium were up to 60 times those recorded on the surrounding hills. The frequency of the predominant ground noise dropped from 6 to 8 Hz to 3 or 4 Hz in the areas of greatest amplification. From the relative increase in microseismic noise at different frequencies, it appears that the alluvium in the southern suburbs of Dunedin is between 50 and 300 m thick (auth.)