The effect of Lake Benmore on local earthquakes

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Adams, R.D. 1973 The effect of Lake Benmore on local earthquakes. [s.l.]: [s.n.]. Report / Geophysics Division 81 15 p.

Abstract: Lake Benmore, with a capacity of 2,040,000,000 cubic m and a maximum depth of 96 m, is New Zealand's largest artificial reservoir. No obvious seismic effects were apparent at the time of its impounding in December 1964, but statistical studies of routinely located earthquakes show a significant increase in earthquake activity since then. The frequency of earthquake occurrence within 80 km of the dam has increased by a factor between 3 and 6, with a significance of 97% to 98%. The distribution of post-impounding earthqaukes suggests that activity is concentrated near the dam, and falls off with distance out to about 60 km, beyond which it remains constant. Most post-impounding earthquakes are concentrated in the area upstream of the dam and within 40 km of it. Within this area there is no clear correlation between epicentres and surface geology, but one linear trend of earthquakes runs in a north-easterly direction from the north of the reservoir. The two largest post-impounding earthquakes were of magnitude 5.0. These occurred 1 1/2 and 6 1/4 years after impounding, and were both within 20 km of the dam. Further detailed studies of small earthquakes near Lake Benmore are proposed, and also a full surveillance of any seismic effects are proposed, and also a full surveillance of any seismic effects accompanying the planned raising of Lake Pukaki in 1976 (auth.)