Edgecombe earthquake

Reconnaissance report

Abstract

On March 2 1987, at 01h 42m 34s UT an earthquake of magnitude (ML) 6.3 occurred near 37.91°S, 176.79°E close to the town of Edgecumbe in the North Island, New Zealand. The depth is provisionally estimated to be 12 ± 1 km. Seismic activity in the general area during the previous week culminated in a foreshock on March 2 of ML 5.2 at 01h 35m 37s. Four aftershocks with magnitudes in excess of 5.0 occurred on March 2 at 01h 51m 08s (ML 5.6), 02h 07m 23s (ML 5.1), 06h 56m 32s (ML 5.2) and 07h 55m 09s (ML 5.2).

The earthquakes occurred at the end of summer after a long period of dry weather.

Modified Mercalli Intensities of MM IX have been reported in and around Edgecumbe, with possible instances of MM X. Strong motion accelerographs recorded peak ground acceleration of up to 0.33 g within 15 km of the epicentre. The main shock produced a complex series of surface scarps, the longest being about 7 km long striking SW from Edgecumbe. About 1.3 m maximum extension occurred across the scarp with the area to the north-west being downthrown by about a maximum of 1.5 m which continued to subside slowly. Other smaller normal fault traces have also been detected as well as compressional rolls.

There was extensive evidence of level ground liquefaction and lateral spreading near rivers. Both these phenomena produced eruption of sands at the ground surface. Some wells were observed to have increased flows or increased pressures whilst others were had decreased flows.

General regional subsidence of the alluvial plains in the area up to 2m has been confirmed by levelling completed within three weeks of the earthquake.

Structural damage was confined to the alluvial plains in which the town of Edgecumbe is centred. The depth of sediments on the plains is not less than 350 m.

There was extensive minor damage to roads. Severe damage to many houses and other single storey structures. A dairy factory complex in Edgecumbe, two paper mills in Kawerau and a paperboard mill in Whakatane all sustained damage, in some cases considerable. At present information on the damage in the paper mills is not available.

References

Beanland, S. and Blick, G., (1987),"Edgecumbe Earthquake, March 2, 1987 – earth deformation studies, March 3-12, 1987", NZ Geological Survey. Earth Deformation Section, Immediate Report 87/02.

Cooney, R.C., (1978), "The structural performance of houses in earthquakes", Bulletin of the NZ National Society for Earthquake Engineering 12(3), pp. 223-237.

Cooney, R.C., (1980), "The Te Aroha storm of 19 July 1978 - damage to buildings", Technical Paper P29, Building Research Association of New Zealand.

Cooney, R.C. and Fowkes A. H. R., (1981), "New Zealand houses in earthquakes - what will happen", Proceedings of the conference on large earthquakes, Napier.

Cooney, R.C., (1982), "Strengthening houses against earthquake - a handbook of remedial measures", Technical Paper P37, Building Research Association of New Zealand.

Grapes, R.H., Sissons, B., and Wellman, H.W., (1987), "Widening of the Taupo Volcanic Zone, New Zealand", Submitted for publication to Geology.

Healy, J., Schofield, J.C. and Thompson, B.N., (1964), Sheet 5 Rotorua (1st Ed.), "Geological Map of New Zealand 1 : 250,000", Department of Scientific and Industrial Research, Wellington, New Zealand

Kuribayashi, E., and Tatsuoka I. F., (1975), "Brief Review of Liquefaction during Earthquakes in Japan", Soils and Found., 15 (4), 81-92. DOI: https://doi.org/10.3208/sandf1972.15.4_81

Smith, E. G. C. and Webb, T. H., (1986), "The seismicity and related deformation of the Central Volcanic Region, North Island, New Zealand", Bulletin 23, Royal Society NZ, "Late Cenozic Volcanism in NZ", (edited by I.E.M., Smith), 112-133.

SANZ, (1978), "Code of practice for light timber frame buildings not requiring specific design" NZS 3604 (current edition 1984).

Woodward, D.J., (1985), "Seismic reflection survey on the Rangitaiki plains, Eastern Bay of Plenty", Geophysics Division, Department of Scientific and Industrial Research.

Published
1987-09-30
How to Cite
Pender, M. J., & Robertson, T. W. (1987). Edgecombe earthquake. Bulletin of the New Zealand Society for Earthquake Engineering, 20(3), 201-249. https://doi.org/10.5459/bnzsee.20.3.201-249
Section
Articles