Fact sheets compiled and distributed by the Institution of Professional Engineers of New Zealand The earthquake GNS Science believe that the earthquake arose from the rupture of an 8 x 8 km fault running east-northeast at a depth of 1-2 km depth beneath the southern edge of the Avon-Heathcote Estuary and dipping southwards at an angle of about 65 degrees from the horizontal beneath the Port Hills.
The amount of slip between the two sides of the fault was up to 1.5 m. The Port Hills have risen by about 40 cm, the mouth of the estuary has moved westward by a few tens of cm, and the land just north of the estuary by tens of cm to the east. Land west of the estuary, and the estuary itself, will have sunk by roughly 10 cm as a direct result of the fault rupture. However, there may be additional subsidence on top of this as a result of ground compaction during the strong shaking.
Earthquake records show that some buildings may have experienced shaking more than two times more intense than a new building would be currently designed for, but perhaps for a lesser duration than envisaged by the loadings code (NZS 1170.5). The intensity of shaking appears to have died out rapidly as it travelled westwards from the fault.