The Wellington region is tectonically active and criss-crossed by many faultlines. While we often feel small earthquakes that don't cause much damage, many of the active faults in the region are actually capable of producing large earthquakes.
In 1855, the Wairarapa Fault ruptured causing a magnitude 8 (on the richter scale) earthquake. About 5000 km 2 of land was shifted vertically, with uplift of 6 metres near Turakirae Head and 1-2 metres in the Wellington harbour. The main quake shook for 50 seconds and was followed by hundreds of aftershocks greater than magnitude 5 in the following few weeks.
A large, shallow earthquake along the Wellington fault, say magnitude 7.4, would cause strong shaking and considerable damage around the region. If it happened during the day there could be about 500 deaths, 4,000 injuries and perhaps 1,800 people trapped.
If the earthquake hit at night, fewer people would be hurt. We could expect over 100,000 buildings to be damaged in some way. It could cost $4 billion to repair and rebuild Wellington and the surrounding areas.
Greater Wellington's combined earthquake hazard maps bring together the separate components of earthquake risk (such as ground shaking, active faulting, slope failure, liquefaction, and tsunami potential) into single maps for Wellington, Porirua, Hutt Valley and Kapiti.
The purpose of these maps is to provide better information about the risks from a major earthquake and help find ways in which these risks can be reduced. The maps will be of particular interest to emergency management professionals, local authorities, planners, engineers, and insurance companies.
The maps were developed in painstaking detail by dividing each metropolitan area into 10m x 10m grids. For each grid cell, the expected damage to a typical slice of infrastructure from each hazard component was determined and combined with the other components to provide an overall assessment for that particular cell.
The combined value for each cell formed the basis for the colour-coded map. The colour codes show the relative hazard level.
Davey, R.A. and Shephard, R.B. 1995. Earthquake Risk Assessment Study: Works Consultancy Services, Greater Wellington Regional Council
Ian Brown and Associates Ltd. 1996. Seismic hazard maps series: Combined Earthquake Hazard Maps. Wellington: Greater Wellington Regional Council
Kingsbury, P.A. and Hastie, W.J. 1993. Liquefaction Hazard Maps. Wellington: Greater Wellington Regional Council
Kingsbury, P.A. and Hastie, W.J. 1995. Earthquake Induced Slope Failure Hazard Maps. Wellington: Greater Wellington Regional Council
Kingsbury, P.A. and Hastie, W.J. 1992. Ground Shaking Hazard Maps. Wellington: Greater Wellington Regional Council