1987 Edgecumbe earthquake

Main event

The main shock was preceded for two weeks by earthquake swarms in two areas of the Bay of Plenty. A swarm started on 21 February off-shore from Maketu, near Te Puke, 40 kilometres from the main shock's epicentre, and another swarm started on 26 February between Matatā and Thornton, very close to the epicentre. Then there was a 5.2 earthquake at 1.35 pm on 2 March, followed by the main shock seven minutes later. The largest aftershock measured 5.6 and struck nine minutes later at 1.51 pm.

Eleven ground-surface ruptures occurred in the Rangitaiki Plains, though no active faults had previously been recognised on the Plains. The largest rupture, the Edgecumbe Fault, was 7 km long and formed on, and extended, a late Holocene fault scarp. The intense ground shaking led to a large number of ground surface failures, including sand boils, ridge-top shatters and debris avalanches on steeper slopes.

The Rangitaiki Plains is part of the Whakatāne Graben and both lie within the Taupō Volcanic Zone, which is widening and subsiding. During the Edgecumbe earthquake, the area widened by 1.2 metres and dropped in height by 2 m.

The most damage was in the towns of Edgecumbe, Te Teko, Kawerau, Matatā and Thornton, where chimneys toppled and poorly constructed houses were seriously damaged. The hardest hit was Edgecumbe, with damage to approximately 50% of its houses. There was extensive damage to its milk factory, with large storage tanks toppled. Railway tracks in the town were bent and buckled, and an 80-tonne New Zealand Railways DC class locomotive toppled over.

Twenty-five people suffered injuries that needed medical attention, but no-one was killed. The foreshock seven minutes before the main shock had cut the power supply, and many people had moved away from heavy machinery and out of buildings that then collapsed in the main earthquake.

Gallery

File:Edgecumbe Earthquake Memorial Stone.jpg|Commemoration plaque File:Edgecumbe earthquake001.jpg|Damaged Railway tracks File:Edgecumbe earthquake002.jpg|Damaged Railway Tracks File:Edgecumbe quake006.jpg|Toppled over DC class locomotive File:Edgecumbe quake008.jpg|Fractured farmland

References

References

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2. "M 6.5, Edgecumbe, 2 March 1987". [[GeoNet (New Zealand).
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4. Staff, New Zealand Department of Scientific and Industrial Research. (1987). "The March 2, 1987, earthquake near Edgecumbe, North Island, New Zealand". Eos.
5. (1987). "Edgecombe {{bracket". Bulletin of the New Zealand National Society for Earthquake Engineering.
6. (1989). "Ground damage and seismic response resulting from the 1987 Edgecumbe earthquake, New Zealand". New Zealand Journal of Geology and Geophysics.
7. Franks, C.A.M.. (1988). "Engineering geological aspects of the Edgecumbe, New Zealand earthquake of 2 March 1987". Quarterly Journal of Engineering Geology.
8. (2 March 2017). "1987 Edgecumbe Earthquake: 30 years ago today". [[GeoNet (New Zealand).
9. (1990). "Normal faulting in a back arc basin: geological and geodetic characteristics of the 1987 Edgecumbe earthquake, New Zealand". Journal of Geophysical Research: Solid Earth.
10. McSaveney, Eileen. (16 November 2016). "Historic earthquakes – The 1987 Edgecumbe earthquake".
11. (1997). "The Geology of Earthquakes". [[Oxford University Press]].