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Statistical studies of earthquakes associated with Lake Benmore, New Zealand
Abstract Lake Benmore, with a capacity of 2.04 · 109 m3 and a maximum depth of 96 m, is New Zealand's largest artificial reservoir. No obvious seismic effects were noted during or immediately after impounding in 1964, and no special seismic monitoring was undertaken. Nevertheless, statistical studies of routinely located earthquakes within 80 km of the dam reveal that since impounding the frequency of shocks has increased by a factor between 3 and 6, with a significance of 97% to 98% on a χ2 test. The post-impounding earthquakes are concentrated near the dam, and upstream from it. The deviation from an even distribution is significant at the 95% level, and the observed distribution suggests that activity decreases with distance out to about 60 km, beyond which it remains constant. The two largest shocks, of magnitude 5.0, occurred 1 1/2 and 6 1/4 years after impounding, and were both within 20 km of the dam. There is no clear correlation between epicentres and surface geology, but preliminary field studies have shown that micro-earthquakes are still occurring near the positions of the two largest shocks. It is hoped to carry out a detailed seismic monitoring of the unusual situation at nearby Lake Pukaki, where a natural lake 70 m deep will be raised an additional 38 m in 1976, increasing its volume by 5.5 · 109 m3.
Statistical studies of earthquakes associated with Lake Benmore, New Zealand
Abstract Lake Benmore, with a capacity of 2.04 · 109 m3 and a maximum depth of 96 m, is New Zealand's largest artificial reservoir. No obvious seismic effects were noted during or immediately after impounding in 1964, and no special seismic monitoring was undertaken. Nevertheless, statistical studies of routinely located earthquakes within 80 km of the dam reveal that since impounding the frequency of shocks has increased by a factor between 3 and 6, with a significance of 97% to 98% on a χ2 test. The post-impounding earthquakes are concentrated near the dam, and upstream from it. The deviation from an even distribution is significant at the 95% level, and the observed distribution suggests that activity decreases with distance out to about 60 km, beyond which it remains constant. The two largest shocks, of magnitude 5.0, occurred 1 1/2 and 6 1/4 years after impounding, and were both within 20 km of the dam. There is no clear correlation between epicentres and surface geology, but preliminary field studies have shown that micro-earthquakes are still occurring near the positions of the two largest shocks. It is hoped to carry out a detailed seismic monitoring of the unusual situation at nearby Lake Pukaki, where a natural lake 70 m deep will be raised an additional 38 m in 1976, increasing its volume by 5.5 · 109 m3.
Statistical studies of earthquakes associated with Lake Benmore, New Zealand
Adams, R.D. (author)
Engineering Geology ; 8 ; 155-169
1974-02-11
15 pages
Article (Journal)
Electronic Resource
English
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