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.
Highlights
The damage to housing can be broadly put into two categories, being that which occurred to the basic load resisting elements of houses and referred to as 'structural damage', and that which occurred to other parts and to contents in the houses, referred to as 'nonstructural '
In the case of the Tower Block, vibro-flotation down to a depth of approximately 16 feet was used, whereas in the case of the Medical Services Block, a full basement was excavated below existing ground surface, surface, a further excavation 5 feet below that was undertaken which was backfilled with sand in layers and compacted to maximum density as the filling took place
Most of the damage at Edgecumbe was to transformers that do not appear to have been designed to current Electricorp earthquake standards for electrical equipment
Summary
On March 2 1987, at Olh 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. There was extensive evidence of level ground liquefaction and lateral spreading near rivers. Bakker was in her home, situated on the high ground behind Awakeri and overlooking the Rangitaiki plains, when the earthquake struck. Gaps were opening up in the walls and even the toilet started disappearing. It was just like somebody was sucking it down through the floor. The windows were pinging and you should have heard the noise when the bricks from the outside wall started to fall", Mrs Bakker said. I thought I should get into the car but the car was moving away."
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